F., which is much colder than that produced by the evaporation of the mixture of solidified carbonic acid and ether, 225, and is the lowest temperature ever observed. 227*. The cold produced by the evaporation of the liquefied Gases applied to the manufacture of Ice. The liquefied gase being retained in this state only by the influence of great pie sure, when this pressure is removed, tend to evaporate wi; 227*. Show how the liquefied gases may be used for the manufacture of Ice. Es plain this process iii the case of Ammonia. APPLi: D TO THE MANUFACTURE OP ICE. % 3 extreme rapidity. By this rapid change of state, so much heat is absorbed and made latent in the immense amount of - vapor which is suddenly formed, that the temperature of all surrounding objects is greatly reduced. It has been shown, 224, that it is by the sudden evaporation of liquefied carbonic acid, that the freezing of a part of the liquid acid is accom- plished. The same principle may be applied to the freezing of other liquids, and advantage is sometimes taken of this method of reducing temperature for the manufacture of Ice on a large scale, for commercial purposes. The gas usually selected for liquefaction is Ammonia. This substance is a compound of hydrogen and nitrogen, and is rep- resented by the symbol NH 3 . At ordinary temperatures, it is a gas, but if expo-ed to a pressure of 6^ atmospheres, or 97^ pounds to the square inch, or to a temperature of 40 F., i. e. to 72 below the freezing point of water at 32 F., it is condensed into a clear liquid, which at 103 F. is frozen into a white crystalline solid. When this liquid Ammonia is al- lowed to evaporate intense cold is produced. For the produc- tion of gaseous Ammonia, resort must be had to some of the compounds which contain it. The most convenient substance for this purpose, is the common Aqua Ammonia of commerce, which is nothing but a solution of gaseous Ammonia in water. "Water has the power of absorbing seven hundred times its volume of this gas, without undergoing any very great increase in bulk ; i. e. one cubic inch of water will absorbabout seven hun- dred cubic inches of Ammonia, ow- ing to the strong af- nity of water for this gas, and thus a very large amount of the gas is, by chemical means, compressed into a very small ^ compass. If this solution of Ammonia be con- fined in one arm of Liquefaction of gaseous Ammonia by pressure and cold. gtronff bent tube m, Fig. 95*, and exposed to a gentle heat over a lamp or fire, the gas is discharged in immense quantities, and by the power- 204 CARRE'S ful pressure which it exerts upon itself, and by cold, may easily be condensed into a liquid and distilled over info the other arm n of the curved tube, kept cool by immersion in a mixture of ice and salt, while the water in which it was dis- solved is left behind. If this arm of the tube be now taken from the fire and immersed in cold water, its temperature being at once reduced, the force which expelled the gas from the water is diminished, and the pressure upon the liquefied a-nmonia in n is reduced, so that it begins to evaporate with great rapidity back into the arm m, where it is immediately re-absorbed by the water from which it had been expelled. By the vacuum created by this absorption, an additional amount of the liquefied gas in n is allowed to evaporate, and so the process goes on until the whole of the liquefied Ammonia in n has been re-absorbed by the water from which it had been expelled in m, and the leg n is left perfet-tly dry. By this rapid evaporation, the temperature of n is greatly re- duced, and if immersed in water, while the process is going on, the water is speedily frozen. When this has taken place, the arm m should be a second time heated, the ammonia again expelled and liquefied in the arm w, and then a second time evaporated, and so the process repeated, until all the ice desired has been produced. 228*. Carry's Ice Machine. This extremely ingenious ap- paratus is intended for the manufacture of ice on a large scale by the liquefaction and subsequent evaporation of gaseous Ammonia. It is represented in Fig. 96*, and con- sists of two parts, a generator A, and a receiver B. Aqua Am- monia is introduced into the generator, which is then placed over a fire and the receiver is immersed in a vessel of cold water. The gaseous Ammonia is discharged in immense quan- tities, and passing through the valve o, Fig. 97*, opening up- wards, is conveyed by the tube d to the receiver B, (m is a solid rod intended to strengthen the apparatus,) where, by the com- bined influence of its own pressure and of the cold of the sur- rounding water, it is liquefied, and collected in the small recepta- cles r, r, r. The great heat which is set free by this liquefaction is immediately absorbed and removed by the cold water in which the receiver is placed. The process requires about ] J hours for completion, and is stopped as soon as the thermome- ter t indicates a temperature of 300 F. The apparatus is 228*. Describe the first process in Carre's ice machine. Describe the second process. ICK MACHINE. 205 then taken from the fire and the generator A placed in a vessel of cold water, Fig. 97*. At the same time the vessel of cold water is withdrawn from the receiver B, and it is exposed to the natural temperature of the air. A cylindrical cup containing the wa- ter to be frozen is then placed in the central cavity E of the receiv- er F and covered. As the generator cools, the internal pressure within it and the receiver di- minishes, and the lique- fied Ammonia at once commences evaporating back from the receiver by the syphon-tube and Ice Machine. First Process. yalye g j nto ^ genera . tor, where it is immediately absorbed by the water from which it had been previously expelled. Fig. 97*. This rapid evapora- tion produces so much cold as to freeze the water, contained in the central vessel E, solid in the course of l hours. By this evaporation of the liquefied Ammonia back into the genera- tor, the liquid which it contains is restored to its original strength, and may be used again and again for the production of the liquefied gas. As a portion of the Carre's Ice Machine. Second Proems. water, about ^tll, dis- tills over with the gaseous Ammonia when it passes from the gen- erator to the receiver, from which it does not all return, when 206 AMOUNT OF ICE PRODUCED. the liquefied Ammonia evaporates back into the generator, the receiver becomes gradually filled with water, arid the quantity contained in the generator becomes correspondingly diminished. To obviate this difficulty, in machines constructed for the manu- facture of ice upon a large scale,' the receiver is placed above the generator, that the water may be drained off and returned, charged with Ammonia, to the generator by the action of gravity, or by a small pump worked by a steam engine. The above is a description of the apparatus as first invented and used upon a small scale. In the large machines intended for the manufacture of ice, all the parts are greatly enlarged and strengthened. The generator is made of iron, strongly hooped with steel bands, so as to be capable of sustaining a pressure of 700 Ibs. to the square inch. A large tank is pro- vided for the reception of the water that surrounds the receiver. The receiver consists of several stacks of tubes, and these are surrounded by a solution of chloride of calcium, a liquid which does not freeze until reduced many degrees below the freezing point of water, and which therefore remains permanently liquid. In this solution and between the tubes of the receiver into which the liquefied gas evaporates, are placed the cans, 24 in number, i filled with the water to be frozen. As the liquefied Ammonia evaporates, into the tubes of the receiver, so much heat is ab- sorbed and rendered latent that the temperature of the solution .of chloride of calcium in which the cans are immersed is speedily reduced many degrees below the freezing point of water, 32F., and, as a result, the water contained in the cans at the expira- tion of four hours is completely frozen. The cans are dipped for a moment in hot water, and then inverted, in order to remove the ice. The blocks of ice are uniformly rect- angular, and as their temperature is far below 32, by simply moistening their surfaces they freeze perfectly to each other, and form solid blocks of any required dimensions. The water introduce 1 into the cans is perfectly pure, being obtained by distillation from the water contained in the boiler of the steam engine. The ice therefore is perfectly pure, is very hard and compact, and is much longer in melting than natural How is the water which goes over into tho receiver returned to the generator? De scribe the arrangement of Carre's Ice machine for actual use upon a large scale for the manufacture of ice. Why is a solution of chloride of calcium employed ? How is the Ice extracted from the cans in which it is frozen? How are large solid blocks formed ? State the amount of ice that may be produce! by these machines. State the cost per 'pound. PRESSURE EXERTED BY THE LIQUEFIED GASES. 207 ice. The ice can also be made at a very small expense. At the Louisiana ice works, in New Orleans, six machines produce from 72 to 76 tons of solid ice every 24 hours, at an expense of $3 per ton. It is estimated that about eight pounds of ice may be produced for one cent. At this cost, one-half cent per pound for the ice would yield a large profit. The ice made by this process, under the direction of M. Bujac, is used by seven- eighths of the population of New Orleans, and is also extensively exported to Mexico and Texas. Millions of pounds have been manufactured and consumed. It is evident that this process is possessed of very great value to the inhabitants of all hot climates, not simply for the manufacture of ice, but for the cooling of the air of apartments and of refrigerators. 227. Pressure exerted by liquefied Gases. In order to estimate the pressure which the condensed gases exerted upon the interior of the tubes in which they were contained, and to de- termine the force requisite to overcome the repulsive energy of their own particles in the gaseous state, small air gauges were enclosed in the condensing tubes. The pressure was estimated by the degree to which the air in the gauges was compressed. Many of the liquefied gases expand upon the application of heat more rapidly than in the gaseous state. It has also been found that Marriotte's law, that the elasticity of a gas increases directly with the pressure, although correct for pressures at a considerable distance above the point of condensation, does not hold good as this point is approached ; in this case the elasticity is not proportioned to the pressure, but is considerably less ; be- cause the repulsion between the particles, owing to the diminu- tion of distance, is no longer able to overcome the attraction of cohesion, this attraction increasing in power the more nearly the point of condensation is approached. These experiments have been prosecuted with great success by Cagniard de la Tour. Various liquids, such as water, alcohol, and ether, were enclosed in strong glass tubes, hermetically sealed, so as to fill somewhat less than one-fourth their capacity. These were then cautiously heated ; the liquids expanded until their bulk was nearly doubled ; expansion then ceased, in consequence of the immense pressure to which they were subjected, and then as the heat was increased, they suddenly passed into the state of vapor and disappeared. Water was found to become gaseous in a space Name the gases which have resisted all attempts at solidification. 227 How is the pressure in the interior of tubes in which gases are condensed estimated? At what rate do the liquefied gases expand ? Describe the experiments of De la Tour. 208 THE CONSTITUTION OF THE GLOBE DEPENDS ON equal to about four times its original bulk, at a temperature of about 773 F., that of melting zinc. As the vapors cooled, suddenly a sort of cloud filled the tube, and in a few moments after, the liquid reappeared. Space must be allowed for the full expansion of the liquid, otherwise the strongest vessels will give way. Thus it has been ascertained, from these and other experiments, that there exists for every liquid a temperature at which no amount of pressure will retain it in the liquid state, but it will inevitably assume the form of a gas. This being true, it is not strange that for some gases there is a temperature above which no amount of pressure is sufficient to reduce them to the liquid state. These are the gases which, like air and oxygen, have remained uncondensed, whatever the pressure to which they have been subjected. 228. The present constitution of the Globe entirely depend- ent on its temperature. From these and other experiments, we justly conclude that the state of matter, as solid, liquid, or gaseous, depends chiefly on the temperature to which it is sub- jected. At a sufficiently high temperature, the most infusible forms of matter, such as refractory minerals, and the metal platinum, would naturally exist in a state of vapor, as aeriform fli'ds, perhaps, colorless, inodorous, and invisible. And at a former period in the history of our planet, it is, chemically speaking, not impossible that all the matter of which the earth consists may have been in an invisible and aeriform state, or perhaps a nebulous mass. On the other hand, at a sufficiently low temperature, probably the most volatile of substances, like the atmosphere and oxygen and hydrogen gases, would eventu- ally become as solid as the most solid rocks and metals, and all the aeriform fluids be condensed. In such a state of things there would be no atmosphere and no water, nor any other sub- stanee on the face of the whole earth, whose particles would possess any power of movement among themselves. Either of these extreme temperatures would be fatal to the existence of man and animals, as well as to that of plants, and strip the earth of everything pleasant to the eye, as well as of all articles good for food. That neither of these extremes exists, but ex- actly that happy mean in virtue of which all the three states of matter can exist and co-exist side by side, the solid rock, the liquid water, the gaseous atmosphere, is surely a conspicuous proof of most refined design in the arrangement of the realm 228. Show that the present constitution of the globe is entirely dependent upon its temperature. I , ITS TEMPERATURE. EXPEHIMENTS. " 209 of Nature, and a sure proof to us of the goodness and the beneficence, as well as of the wisdom and power of the Creator. Experiments : Effects of Heat: Evaporation, 1. Evaporation. Heat Is absorbed in the process of evaporation, as well as that of ebullition. This may be shown by dropping ether upon the bulb of a thermometer : the mercury falls, because its heat is absorbed by the vaporization of the ether. 2. The rapidity of evaporation is greatly increased by the removal of the atmospheric pressure. Place ether under the receiver of the air pump, and exhaust the air : the ether begins to boil, and a thermometer introduced into jt sinks below 82o. 3. Pour ether upon the surface of water in a watch glass, and evaporate rapidly by means of the air pump : the water will be frozen. The watch glass should be placed in the interior of a large vessel, also filled with ether. To make these experiments succeed with promptness the water, ether, and sulphuric acid, as well as the vessels employed, should be previously cooled by being placed on ice. The watch glass should be supported upon a ring of tin. wound with woolen cloth. 4. Place water in a watch glass, in strong sulphuric acid, and exhaust the air by an air pump. The water will be frozen by its own evaporation. The vapor, as fast as it rises, is condensed by the sulphuric acid. The air pump must be kept very steady. 5. A single drop of water placed on the plate of an air pump may be frozen simply by its own evaporation ; also a single drop of water placed upon a piece of burnt cork, hol- lowed upon its upper surface. 6. Provide an unbaked clay cup, one of the cups of Grove's battery will answer very well, pour water into it, and introduce a thermometer As the water percolates through the cup and evaporates, the thermometer sinks. The effect is greater if ether or alcohol are used. 7. Drop ether or alcohol upon the bulb of the large air thermometer, previously de- scribed, Fig 45, and the sinking of the liquid in the stem will be very marked. 8. Place deep wine glasses of water, alcohol, and ether, under the same receiver of an air pump, with a thermometer in each, and note the difference in the cold produced when the air is withdrawn, owing to the difference in the rate of evaporation. 9. If ether be allowed to fall, drop by drop, upon a thin vial of water, covered with muslin, in a current of air like that produced by a bellows, the water will be fiozen. 10. That heat is absorbed by evaporation, under all circumstances, is shown by the cryophorus of Dr. Wollaston. The empty bulb must be placed in a freezing mixture of equal parts of snow and salt ; the vapor within it is condensed ; rapid evaporation takes place from the liquid in the other bulb, and it soon freezes. Eoth bulbs should be pro- tected from draughts of air, and previously somewhat cooled ; the experiment should not be attempted in a warm room. 1 1. The pulse glass held in the hand, as soon as it boils, produces a sensation of cold, on the same principle. 12. The water hammer, made to boil in the same way, also illustrates the same truth. 13. That the amount of moisture existing invisibly in the air depends upon its tem- perature, may be shown by placing a bottle of moist air, tightly corked, upon ice and salt, in a bowl. As the air cools, a cloud appears within the bottle, 14. Ice and snow mixed, and placed in a jar, will soon induce a deposit of moisture on the outside, from the air, which is cooled by contact with it. 15. The Dutch weather house; the sponge balance hygrometer; the hygrometer of Saussure, may all be used to demonstrate the varying amount of moisture in the air, by removing them from a damp to a dry atmosphere, and the reverse. 16. Daniell's hygrometer will illustrate the same fact on a different principle. 17. Place a square piece of copper upon the surface of a mixture of ice and salt, and observe the minute drops of moisture formed. This illustrates the mode in which dew is formed upon the earth, the difference being that in one case the copper is cooled by the ice, in the other the earth is cooled by radiation. 18. Expose different plates of different substances, such as glass, wood, rough copper, polished copper, all of the same size, on a cool night in summer, and observe the different amounts of dew collected upon them. 19. Place a thermometer upon the ground on a clear night, suspend a second ther- mometer 10 or 12 feet above it, in the air. and note how much lower the first sinks than the second, showing that dew is caused by the radiation of the heat of the earth, and not by the general coolness of the atmosphere. 20. Solidified Carbonic Acid. The dry solid acid may be held in the hand with impunity ; mixed with sulphuric ether, it is dangerous to handle. 210 SPECIFIC HEAT. 21. Place a small quantity on stout plate glass, no effect takes place so long as it re- mains dry ; pour ether on it and the glass is broken at once by the intense cold which is produced. 2avoisier and Laplace. Describe a more simple mode of determining the same thing by a vessel of ice. CALORIMETER OF LAVOISIER AND LA PLACE. 215 In the inner is placed the substance whose specific heat is to be determined, having been previously heated to 212 by im- mersion in boiling water. The two exterior compartments, A and B, are filled with pounded ice ; the ice of the compartment A, is intended to be melted by the hot body, M ; the ice in the compartment B, is intended to cut off the radiant heat of the external air, in order that the ice melted in A may be due solely to the heat proceeding from the body M. Two stop-cocks are provided, D and E, for the purpose of drawing off the water. The hot body is first introduced, and covered with a double lid ; the stop-cock D is then opened, and the water formed allowed to trickle into a measuring glass. When the temperature of the hot body has fallen to 32, the water will cease running, and the amount is then carefully measured and compared with that produced by the cooling of an equal weight of water from 212 to 32. It has been objected to this instrument, that a portion of the water formed is detained by adhesion within the inner vessel, and that a portion may be ? 97. frozen a second time, and thus the indica- tions of the instrument may be vitiated. A more simple mode of determining specific heat is to place the body previously heated to 212, in a piece of ice which has been scooped out to receive it a Fig. 97, and covered with a lid, b, of the same mate- rial. When the substance has cooled to Specific Heat. 32, the water should be poured out and measured ; this amount compared with that produced by an equal weight of water in cooling from 212 to 32, will give the specific heat required. 235. Specific heat determined by the rise of temperature produced by the immersion of equal weights of different bodies, for the same time in equal weights of water. In this process, equal weights of water and of the substances in question are heated to 212, and then immersed for the same length of time, in equal weights of water, of exactly the same tempera- ture. The difference in the temperature of the water, contained in the different vessels, will give the specific heat. The differ- ence in the time required for heating the water in each vessel an equal number of degrees by the different substances, will give the same result. 23o. Show how specific heat may be determined by the number of degrees of heat im- parted to water in the same time. 216 SPECIFIC HEAT OF SOLIDS 236. The specific heat of Water. The specific heat of water, or the capacity of this substance for heat, is greater than that of any other liquid, and also of all solids, and consequently to change the temperature of large masses of water, is a work of time. Water may have a very large amount of heat poured into it without any perceptible effect upon its temperature. And on the other hand, a vast amount of heat may be abstracted from water without any sensible diminution of its temperature. This is due to its immense capacity for heat. Water, therefore, in consequence of the slight effect produced upon it by varia- tions of atmospheric temperature, would make a very poor ther- mometric fluid. Mercury, on the contrary, whose specific heat, or capacity for heat, is 33 times less than that of water, yields to the slightest change of temperature, and is therefore admira- bly adapted to thermometric purpose*. The susceptibility of bodies to changes of temperature is always in the inverse pro- portion to their specific heat. 237. Specific Heat of Solids. The determination of the specific heat of bodies is necessarily attended with great diffi- culty, owing to the variety of the sources of error, and the num- ber of precautions required; and much careful consideration and experiment has been bestowed upon it. The following table gives some of the results of M. Regnault, one of the most successful of the later experimenters on this subject, ob tained by the processes of immersion and mixture, and they bring to light some very curious facts : Specific Heat of Solids of equal weight between 32 and 212. Water, 1. Charcoal, 0.24150 Glass, ...... 0.19768 Iron, 0.11879 Zinc, 0.09555 Copper, 0.09515 Brass, 0.09391 Silver, 0.05701 Tin, 0.05623 Mercury, 0.03332 Platinum, 0.03243 Gold, 0.03244 Lead, , 0.03140 238. Specific heat of Liquids. The specific heat of liquids is determined by the same methods as that of solids. Water is taken as the standard, and the specific heat of all other liquids is compared with it. The specific heat of water is greater than that of all other liquids, without exception. A body in the 233 How does the specific heat of water compare with that of other bodies ? What are some of the results of this peculiarity ? 237. Give som of the results of Regnault's table. 238. How is the specific heat of- liquids determined? Give the table. AND LIQUIDS. 217 liquid state has a higher specific heat than the same substance when in the solid form. This is very marked in the case of water, in which the specific heat is double that of ice, water being 1.000, ice is 0.505. Table of Specific Heat of Liquids. Water, 1.00000 Oil of Turpentine, . . 0.42593 Alcohol, 0.615 Ether, , 0.5113 Bi-Sulphide of Carbon, Bromine, Chloroform, 239. Specific heat of Gases. The determination of the spe- cific heat of gases is attended with unusual difficulties, on ac- count of the facility with which their bulk and weight are influ- enced by external circumstances, and though conducted by many philosophers of distinguished experimental skill, the best results can be viewed only as approximations, requiring to be corrected by future research. Dr. Crawford, the first careful experimenter on this subject, conducted his experiments in the following man- ner. He selected two copper vessels, made as light as possible, and exactly of the same form, size and weight, exhausted one of them, and filled the other with the gas, to be examined. They were heated to the same temperature by immersion in the same vessel of hot water, and then plunged into equal quantities of cold water, of the same temperature. Each flask heated the water ; but while the exhausted flask communicated solely the heat of the copper, the other gave out the heat of the copper plus that of the gas which it contained. The number of de- grees by which the cold water was heated by the former, deducted from the number of degrees by which it was heated by the latter, gave the heating power of the confined gas. By repeating the experiment, with air and different gases, their comparative heating powers, or specific heats, were ascertained. These experiments, though correct in principle, are not consid- ered reliable, on account of the superior heating influence of the copper globes compared with the small amounts of gas that were employed. The same subject was next investigated by Lavoisier and Laplace, with the aid of their calorimeter ; 234. A current of gas was transmitted through a spiral tube placed in boiling water, in order to be heated to a fixed temperature, and was then made to circulate within the calorimeter, in a similar 239. How is the specific heat of gases determined? Describe Crawford's process. De- scribe Lavoisier's method. 218 SPECIFIC HEAT OF GASES. tube, surrounded by ice. Its temperature, in entering and quit- ting the calorimeter, was noted by means of thermometers, and the number of degrees of heat lost in cooling from 212 to 32 was estimated by the quantity of ice liquefied. These experi- ments, though very ingenious, and conducted with great care, are thought to be inaccurate, for the reason previously given, that, in the use of ice, a portion of the water formed may be frozen a second time in consequence of the low temperature of the apparatus, and a portion also detained and prevented from escaping into the measuring glass, by the adhesive action of the ice. A similar set of experiments was afterwards undertaken by Delaroche and Berard. They transmitted known quantities of gas, heated to 212. in a uniform current through the calo- rimeter, and instead of ice, surrounded the serpentine tube with water. The temperature of the gas, at the moment of its exit, was carefully noted, and the number of degrees of heat which it imparted to the water, in cooling from 212, was also carefully ascertained by delicate thermometers. The results of their experiments are contained in the following table, which for a long time was thought to furnish the most accurate determina- tion of the specific heat of gases. Equal weights of the gases were used in all cases. In the first column the specific heat of water is taken as the standard of comparison ; in the second column the specific heat of air is taken for the standard : Delaroche and Berartfs Table of the Specific Heat of Gases. - jt Gases, equal weights. Water the Standard. Air the Standard. Water, 1.0000 8470 / Air, 0.2669 1 0000 0.2361 0.8848 0.2754 1 0318 3 2936 1 3400 Protoxide of Nitrogen, .... Heavy Garb. Hydrogen, . . , 0.2369 0.4207 2884 0.8878 1.5763 1 0805 Carbonic Acid, ..... 0.2210 0.8280 It is very evident, from this table, that equal weights of the different gases differ very much in the quantity of heat which they contain. The specific heat of hydrogen is twelve times Describe that of Delaroche and Berard. Give some of the results of their table. How does the specific heat of hydrogen compare with that of other gases, and even with the metals. REGXAULT'S TABLE. 219 greater than that of air ; that of nitrogen and oxide of carbon about the same as air. Compared with water, the specific heat of hydrogen is more than three times greater, and larger, than that of any other known substance. Out of nine gases, on which experiments were made, none, except hydrogen, has a specific heat equal to that of water ; but they all have a specific heat much greater than that of any of the metals. Thus hydro- gen, the lightest known substance, has the greatest specific heat, while the metals, the heaviest of all bodies, possess the least. 240. Hegnaults determination of the specific heat of Gases. Within a few years the same subject has been investi- gated by Regnault. The method adopted was, in the first place, to condense the gas in a strong receiver ; a known weight was then allowed to escape at a perfectly uniform rate through a spiral tube plunged into a vessel of hot oil, which was main- tained at a fixed temperature ; the gas was in this way, during its passage through the spiral, raised to a known temperature equal to that of the oil in the bath ; it was then made to pass through a metallic vessel, surrounded by a known weight of water ; and finally, was allowed to escape slowly into the air, ample time being given for its temperature to be reduced to that of the surrounding water. By this process the rise of temperature experienced by a known weight of water when a given weight of each gas, after it had been raised to a fixed standard temperature, was passed through it, was ascertained. The different gases treated in this way, were found to impart unequal quantities of heat to the water, and this became a measure of their specific heat. The results are given in the following table : Regnault n Table of the Specific Heat of Gases. Gases, equal weights. Water the Standard. Water, ....... Watery Vapor, ..... Air, ..,.,.. Oxygen, j , Nitrogen, '\ - Hydrogen, ' . . , f Protoxide of Nitrogen, Heavy Carb. Hydrogen, . . . Oxide of Carbon, ..... Carbonic Acid, ..... 1.0000 0.4750 0.2377 0.2182 0.2440 3.4046 0.2238 0.3694 0.2479 0.3308 ^s 240. Describe Regnault's process. Give some of the results of his table. 220 SPECIFIC HEAT AFFECTED BT On comparing this table with that of Delaroche and Berard, considerable diversity is found, but not more than might be ex- pected from the improved methods of experimentation that have been introduced since their time. The important fact is proved by both tables, that equal weights of different gases of the same temperature, and the same density, contain very unequal amounts of heat, and that there is, therefore, no relation between the thermometric temperature of a body and the actual amount of heat which it contains ; also that the specific heat of hydrogen, the lightest substance known, is not only greater than that of all the gases, but actually nearly 3 times greater than that of an equal weight of water of the same temperature ; and as the specific heat of water is superior to that of every other liquid and solid, it follows that the specific heat of hydrogen is greater than that of any other known substance. 211. The specific heat of a body may be changed by alter- ing: its density. The specific heat of a body is not a per- manent property, but may be altered by changing its density. Any influence which alters the distance between the particles of a body, affects its specific heat. If the particles be brought nearer to each other, specific heat is diminished ; if the parti- cles be separated and removed to a greater distance from each other, the specific heat of the body is increased. If, by mechani- cal compression, the particles of a piece of soft, well annealed copper, whose specific heat varied from 0.09501 to 0.09455, be brought nearer to each other, the specific heat will be found to ba reduced from 0.093 6 to 0.0933; on being again thoroughly annealed, so as to recover its former density, its specific heat will be nearly restored to what it was before, 0.09493 to 0.09479. When water, or any other liquid, is compressed, its specific heat is diminished ; when it is allowed to expand to its former dimen- sions, its specific heat returns to the same amount as before. The same is true of gases ; if they are compressed, their specific heat is diminished ; but if allowed to expand, their specific heat is greatly increased. Regnault denies this in the case of the gases, but his conclusions are in direct opposition to those of Delaroche and Berard, and nearly all other experimenters, and they must, therefore, be received with some hesitation. As the distance between the particles of bodies is very much affected by change of temperature, a removal of the particles from each 241. What effect is produced upon the specific heat of bodies by altering their den- sity ? Give illustrations. What effect is produced upon specific keut by elevation of temperature ? Give the table. CHANGE OF DENSITY OR STATE. 221 other, and expans : on being produced by a rise, while contraction is the result of a diminution of temperature, it follows that the specific heat of a body is greater at a high temperature, than at a low one. This is true of Folids, liquids, and gases. In the ca.e of gases, it is denied by Regnault ; but the correctness of his opinion may be doubted. That it is true of soLds, may be plainly seen from the following table : of Specific Heat with rise of Temperature. Specific Heat from 32 to 212. Specific Heat from 320 to 5720. 0.0330 0.0350 Platinum, 6.0886 0.0355 Antimony, ...... Silver, ' Zinc, Cooper, 0.0507 0.0557 0.0927 0.0949 0.0549 0.0611 O.KH5 0.1013 Iron, ....... 0.1098 0.1218 Glass, 0.1770 0.1900 242- The specific heat cf a body changed by altering 1 its physical state. A body in the liquid state has a higher specific heat than the same substance when in the state of a solid. On the other hand, a substance in the gaseous state has a lower specific heat than the same substance in the liquid state. When ice passes into the liquid state, its specific heat is doubled ; but when water is converted into vapor, its specific heat is dimin- ished one half. Different solids have the amount of their spe- cific heat differently affected by a change of state, and they vary very much among themselves. 2-S.3. A chang-c in the specific heat of a body always chang- es its temperature ! an increase of specific heat diminishes tem- perature, and a diminution cf specific heat increases it- Change of Density, or of the State of bodies, always produces change of temperature- It has been shown, in the case of soft copper, that a change in the specific heat of a body is always produced when a change is made in its density ; if its density be increa ed, its specific heat is diminished ; if its density be diminished, its specific heat is increased. Besides this effect, and as a conse- quence of it, a change in the temperature of the body whose density is altered, is always produced. In the ca?e of soft cop- per, if density be increased, and specific heat diminished, tem- perature rises ; if density be diminished, and specific heat be ^42, What effect is produced upon specific heat by change of state? 243- What effect Jfl produced upon temperature by change of specific heat ? 222 CHANGE OF DENSITY increased, temperature sinks. So great is the effect upon tem- p 'rature, in consequence of a change of specific heat, produced by a change in density, that if a piece of iron be rapidly ham- mered it immediately becomes hot, and by a skillful blacksmith, may even be made red-hot by this process. This rise in temperature may be thus explained. The distance of the particles of bodies from each o;her is in general determined by their specific heat. This specific heat spends its energy in keep- ing the particles apart, and in resisting the attraction of cohesion which is constantly tending to draw them together, and it no longer possesses the power of affecting temperature. When- ever heat is expended in producing any mechanical effect of this kind, it loses its power of affecting the thermometer and t'ie senses, and passes from a sensible to an insensible state. Heat can not produce an effect upon temperature and a me- chanical effect, at the same time. A definite amount of heat m ide to pass into a body may cause the temperature of the body to rise, or it may spend itself in increasing the distance between its particles, and expanding it, but it can not do both at the same moment. Heat which has caused a body to expand, can not at the same time rai-e its temperature. When a piece of ii-on is held near the fire, the first effect of the heat is to expand the iron, and this it does without raising its temperature ; this h?at becomes la f ent in the iron, and the temperature of the body does not ri e unless it receives more heat from the fire than can be employed in effecting expansion. But the heat that has been expended in this manner, and become latent in any substance, is not lo t; it will again become heat of temperature as soon as it is no longer needed for the purpose of keeping the particles of the body apart. If mechanical force should vio- lently compress the body and bring the particles nearer together, the heat which had previously kept them apart being now no longer needed for this purpose, will make itself apparent as heat of temperature. This is what takes place when cold iron is hammered ; the heat which had kept the particles asunder, and which had remained latent while thus expended, being now no longer able to exert this effect, is compelled to appear as heat of temperature, and the iron at once becomes very hot. If, on the other hand, the particles of iron had been separated from each other by mechanical violence, they could not have What effect is produced upon temperature by the compression and expansion of bodies^ Of passing from the solid to the liquid or giseous state ? Give illustrations. Explain toe beating of iron red-hot by hammering. .From what source is this heat derived ? AFFECTS TEMPERATURE. 223 remained permanently separated except by the agency of heat, for which there would be, therefore, an imperative demand. All the heat in the neighborhood would be drawn upon for the purpose of satisfying this demand, and the first source would be the free, sensible heat of the body itself. This would at once be transferred into the latent state, and be expended in main- taining the distance between the particles ; it would cease, therefore, to appear as heat of temperature, and the iron would at once become cold. The quantity of heat latent in the metals, and which becomes apparent when they are compressed, is ad- mirably illustrated by the faint flash of light which is emitted when a bullet from a steam gun strikes a wrought iron target. The bullets are completely flattened, and when directed against a plate of lead placed in front of the target, the two surfaces of lead become firmly united as if melted or soldered together. The fla-h of light is only visible in a darkened room. Another still more striking illustration is seen in the flash of light pro- duced when the 80 Ib. hexagonal bolts fired from the Whit- worth gun strike the thick iron-plated sides of a floating battery, Fig. 98. "Notwithstanding the immense resisting power of the Fig. 98. . The Latent Heat of Iron Shot and Plates rendered Sensible by Compression. iron plates, the hexagonal bolt passed completely through them. The shot when discovered was found to be so hot that no one Explain the heat and light produced by the shot from the Whitworth guns, Givf Ptber illustrations, 224 ILLUSTRATIONS. could touch it, and was ascertained to have been compressed to the extent of an inch in length. It was noticed that at the instant of concussion between the shot and the vessel, a broad S 7 ieet of intensely bright flame was emitted, almost as if a gun hcid been fired from, the vessel in reply" The same effect has been repeatedly noticed when the balls from the heavy Dahlgren guns of the Monitors struck the stone fortifications against which they were directed. The heat, in these cases, was that previously latent in the iron, made sensible by the compression of the metal and the diminution of its specific heat. In like manner, the intense heat which is evolved when iron bars are subjected to the process of rolling, and not unfrequently by the axles of cars and carriages when in rapid motion, and in the processes of boring and planing metals, is due to the same cause. It is the heat previously latent in the metals, evolved and con- verted into heat of temperature by the diminution of their spe- cific heat in consequence of compression. The heat set free in the simple operation of boring a hole with a gimlet, is sufficient to inflame a friction match. The heat produced by the rapid drawing of a string tightly around the ne^k of a glass flask, is sufficient to crack it. And in the whale fishery, the heat evol- ved by the inconceivably rapid motion of the rope over the side of the boat, after the whale is struck, would be sufficient to set it on fire if it were not kept cool by the continual pouring of cold water. In the best constructed steam engines, the bear- ings of the shafts are made hollow, and a steady stream of cold water caused to circulate through them, in order to prevent them from becoming excessively heated, and the axles from ex- panding to such a degree as to be incapable of moving. These are illustrations of a general principle. Whenever any body is expanded, heat is absorbed and temperature sinks. Whenever any body is compressed, latent heat is given out and temperature rises. This is true of solids, liquid*, and gases. Liquids, if com- pressed, grow warm ; if relieved from compression, they grow cold again. Gases, if compressed, grow hot ; if released from compression, temperature declines. So, in like manner, when bodies change from the solid to the liquid or gaseous state, there is an absorption of heat, because of the large amount which is expended in making the change. The difference between the What effect is produced upon temperature of the passage of a solid into the 1'quid and gaseous stite? Of the passage of gases and liquids into the solid state? When :i liquid is vaporized, what effect is produced upon temperature? What when a yapor is coo densed into a liquid? i; FIRE SYKIMiK. 225 amo eubstancoiw ft solid and a< a liquid is that in the lat'er ca.-e the particle-; an- o far removed that, they can slip readily U|K>ii each o:her. This separation can only be inainlained by the addiiion of a large amount of heat. Consequently, when- ever a solid is liquefied there is an immense al> orption of heat, and temperature sinks; whenever a. liquid is solidified, the re- verse takes place and temperature rises. The latent heat no longer required, becomes sensible. When a liquid is \apoi i/ed, heat is absorbed and temperature sinks. When a vapor is con- densed into a liquid, latent heat is given out and temperature rises. 244. The rire Syringe. Those principle* are admirably illustrated by the fire syringe represented in Fig. 99. It con- sists in its most improved Ibrm of a hollow cylinder of glass, into which a piston fits air-tight. Upon the under side of the piston is a cavity to receive, a bit of tinder or punk, or a tuft of cotlon moistened with ether. On driving the piston forcibly down, the tinder will emit smoke, and finally ignite: a match may thus be lighted with ease. This Fig. 99. large amount of heat has proceeded from the air contained in the; cvlinder. By sudden and forcible compression its den- sity is increased, its particles are brought nearer together, the heat previously ex- pended in keeping them asunder and la- tent in the, air is made sensible, becomes heat of temperature, and is sufficient to inflame the tinder. It is an exj eriment strictly analogous to the heating iron red hot by hammering. On rarefying air the opposite effects are obsei ved. The mist observed in the receiver of an air-pump wh'le it is undergoing exhaustion, is a proof'of the production of cold. As the air is withdrawn, that which remains un- dergoes ji corresponding rarefaction. A demand for heat is created to sustain this rarefied stale. A large amount of heat be- comes latent, and temperature sinks SO low that the ino'stiire in the air can no ri,,- Fin Pump. longer remain in the state of vapour, but 244. Di'Bcribo the fire Byrintfo. Explain its principle. 226 APPLICATIONS OF is condensed in minute drops. A thermometer placed in such a receiver rapidly sinks as the air is exhausted, m consequence of the rarefaction, but when readmitted it rises again witn equal rapidity, in consequence of the condensation. It' the blast fiom an air gnn be directed upon a delicate thermometer, the mer- cury will sink at the moment of discharge, owing to the enor- mous expansion of the air. And when steam from a boiler sud- denly issues, under great pressure, from a small aperture into the atmosphere, its instantaneous expansion cools it to such a degree that instead of scalding the hand held in it, as is the case with ordinary steam, it scarcely feels warm. 245. The distribution of temperature in the Atmosphere, the formation and disappearance of clouds, the production of rain and snow explained by change of density in the air. These facts explain the great cold of the atmosphere of the earth at high elevations. In consequence of the diminution of pressure at high altitudes, the air is much more rare than it is at the sur- face of the earth. The sensible heat of temperature which it would possess if it were everywhere of the same density as it is at the surface of the earth, has been absorbed in conse- quence of its rarefaction, and is now latent. The higher we as- cend, the greater the rarefaction, and consequently the greater the absorption of heat, and the lower the temperature. The average depression of temperature is about 1 F. for every 300 feet of ascent. If, therefore, a portion of air from the surface of the earth were suddenly carried to a great altitude, its temperature would fall, its watery vapor be condensed, and clouds be produced, 202. If on the other hand, a portion of air, at a great elevation, were suddenly brought near the earth, its temperature would be greatly elevated in consequence of its condensation, and if it contained mists and clouds, these would disappear. Change of place among portions of the atmosphere is, of itself, able to produce great changes in its temperature, and in its clearness and cloudiness, and this, no doubt, has an important bearing upon many meteorological phenomena. An excellent illustration of these principles is afforded by the fountain of Hiero, as it is called, at Schemnitz in Hungary. A part of the machinery for working the mines consists of a col- umn of water 2 GO feet high, which presses upon a large volume of air, enclosed in a tight reservoir. The air is consequently enormously compressed by the immense weight of the water, 245. How do these principles explain the distribution of temperature in the atmo- sphere ? THESE PRINCIPLES APPLIED 227 amounting to 8,089 atmospheres. "When a pipe communicating with this reservoir of air rs suddenly opened, it rushes out with extreme velocity, and instantly expanding, absorbs, in so doing, so much heat as to precipitate the moisture it contains in a shower of very white, compact snow, a hat held in the blast being immediately covered with it. So strong is the current of condensed air, that the workman who holds the hat is obliged to lean his back against the bank to retain it in its position. The snow in this case is due to the expansion of the air, and the conversion of its heat of temperature into latent heat. 245*. The Sudden Expansion of Compressed Air is Applied to the Manufacture of Ice. Ice machines. Application has been made of the cold produced by the sudden expansion of com- pressed air to the production of ice for commercial purposes. The air is first made to pass through a large chamber filled with porous materials constantly kept moist by means of a stream of water running through it, and is thus heavily charged with watery vapor, this moist air is then powerfully condensed by a large forcing pump driven by a steam engine. The la- tent heat which is evolved by this violent compression, is ab- sorbed, as fa>t as set free, by the watery vapor which the air contains, owing to the immense capacity of water for heat, 236, and thus the temperature of the air is prevented from rising to the height to which it does in the Fire Syringe. 244. It is still further cooled by being made to pass through a sec- ond chamber filled with porous materials constantly kept moist by running water, and then dried by transmission through an additional chamber filled with porous substances perfectly dry, to which it gives up any moisture that it may have carried from the previous chamber. It is then allowed to expand in a compara- tively large chamber, and in so doing, in the course of a minute or two it becomes very cold. Thence it passes on into a long passage, arranged in an ice house protected from the sun, above which are placed the vessels of water to be frozen, where it undergoes a sudden and very great expansion. By the ex- pansion which the air undergoes in passing through this tube, FO much heat is absorbed and made latent, that it becomes intensely cold, the water in the pans is speedily frozen into thick blocks, and a very large quantity of air confined in the What is the average rate of diminution of temperature &s we ascend above the sur- face? Account for the formation of mists and clouds, and for their disappearance on these principles. What illustration is afforded of these principles by the fountain of lliero, at ijchemnitz? Account for the formation of snow when the compressed air rushes out. 245*. Describe the method of man ulac luring ice by the expansion of com- pressed air. 228 TO THE MANUFACTURE OF ICE, ice-house is cooled to such a degree as to become extremely useful for refrigerating purposes. On these principles a ma- chine has been constructed by Windhausen, in Germany, which is capable of producing 4,800 Ibs. or more than 2 tons, every 12 hours, or nearly 5 tons in 21 hours, at a cost of about $2.94= for 2,000 Ibs. Temperature is reduced from 80 to 18 F. The Windhausen machine has been still further improved by Weld, in this country. r lhis is thought to be the most success- ful method of producing ice by artificial means, and in some respects even to surpass Carre's machine. It possesses four great advantages over processes in which Ammonia and other chemical substances are employed; first, that the refrigerating agent being pure air, can be brought into direct contact with the water to be frozen, without the intervention of tubes and vessels, as is the case with Carre's process, and has therefore an opportunity to exercise a much greater cooling effect; sec- ond, that if any leak takes place nothing can escape that will tend to injure the articles intended to be cooled or frozen, while in the case of machines depending upon the use of special chemical substances a sudden leak at an inopportune moment might result in the destruction of a large amount of valuable material, before any efficient remedy could be applied ; third, the cheapness of the refrigerating agent, which being pure air, can always be had in a perfect s afe in every part of ihe globe; fourth, the comparatively low pressure required for condensing the air, and consequently the much less strength and power of resistance required in the apparatus employed. In compressed air refrigerating machines only about 45 pounds pressure to the square inch are required, while in Carry's machine from 120 to 180 pounds to the square inch are necessary, in others as much as 800 or 1200 pound?. Consequently the compressed air machinesdo not require to be nearly as strong, and are much less expensive. The cost of compression is also much reduced by throwing back a portion of the elastic power of the com- pressed air upon the main shaft so as greatly to reduce the actual power required for condensation. In view therefore of the low first co.*t of the apparatus, the cheapness of the refrigerating agent and its purity, the facility of compression, and the large scale upon which the process can How many tons can be produced by Windhausen "8 machine per diem? At what cost per ton 1 Have the compressed air machines any advantages over Carre's machine ? State the four points of superiority. How can the thin shetts pf ice that are produced by these Ice-machines be made into thick blocks 1 AND TO THE CONDENSATION OF VAPORS. 229 be carried on, this method of manufacturing ice by the agency of compressed air is thought to possess great advantages over those which depend upon chemical agents. This method of refrigeration promises therefore to be of great value for the production of ice in hot climates where no natu- ral ice is formed. It must be remembered however that by none of these processes are blocks of ice of any great thickness formed, rarely more than three or four inches, but blocks of any required thickness may easily be formed by freezing several of them togeiher. 246. The condensation of Vapors by pressure is explained on this principle. It is not the permanent gases alone, whose temperature is raised by compression and diminished by ex- pansion. It is equally true of vapors. If vapor, after being separated from the liquid that forms it, be compressed into a diminished volume, or allowed to expand into an increased one, its temperature will be raised in the one case and lowered in the other, and at the same time its elasticity will be increased by the diminution of its volume, and diminished by the increase or' it. It has been stated, 202, that when vapor is subjected to mechanical compression, its elastic force remains unchanged, because a part of the vapor is condensed into a liquid. It is more correct to say, that the first effect of mechanical compres- sion upon vapors is to increase their temperature, by converting their latent into sensible heat. Their elasticity is at the same time increased in proportion to the pressure, but as the elevation of their temperature above that of the surrounding medium, ren- ders it very easy to abstract heat from them, and the instant any heat is abstracted, a portion of the vapor is reduced to the stale of a liquid, this increased elasticity is almost immediately re- duced to the point at which it was before the compression took place, and no perceptible depression is produced upon the height of the mercurial column. On the other hand, when the mechanical pressure upon the vapor is removed, it immediately expands, its temperature is proportionally lowered by the con- version of its sensible into latent heat, heat beg'ns to enter it from the surrounding medium, a portion of the liquid begins to vaporize, and so the process goes on, until as much vapor has been formed as the temperature of the surrounding medium is able to sustain. Consequently, no perceptible elevation takes place in the height of the mercurial column, because the increase 246. State the ei^ht principles that may be deduced from the above mentioned facts. 230 SUMMARY. of elasticity produced by the influx of heat, keeps pace with the diminution produced by the removal of mechanical pressure. The condensation of vapor is then, in all cases, due to the ab- straction of heat, and not to mechanical compression, just as truly as the formation of vapor is due to the addition of heat. In the liquefaction of gases, the process is accomplished by depriv- ing them of heat as fast as their temperature is raised by com- pression. In this manner, so much heat is gradually abstracted as to compel them to assume the form of liquids. In all case^, vapor compressed, rises to the same temperature that would be necessary to produce it, under the same pressure, by the di- rect application of heat. Thus the vapor raised from water at the temperature of 68 has a volume 58,224 times greater than the water which produced it. Now let this vapor, having been separated from the water, be compressed until it be reduced to the volume which it would have had if it had been formed from boiling water, i. e., a volume only 1.696 times greater than that of the water which produced it, and its temperature will rise from 68 to 212 by the conversion of its latent into sen- sible heat, i. e., exactly the temperature it would have been necessary to give it, if it had been formed in the first place of this degrae of pressure and elastic force. This is a conclusive proof, that the sum of the sensible and insensible heat in vapor is the same, whatever the temperature at which it may have been formed. 247> Summary of Principles. Applications. Illustrations. From the phenomena presented by liquefaction, vaporization, solidification, and the compression and expansion of solids, liquids and gases, we may deduce the following important prin- ciples : 1. Change of density always produces change of temper- ature. 2. If a body pass from a denser to a rarer condition, or from the state of a solid to that of a liquid or a vapor, heat is ab- sorbed, and the temperature of surrounding objects sinks. 3. If the reverse takes place, and a body becomes more dense than before, or passes from the state of a vapor to that of a liquid or solid, as when steam is condensed or water freezes, heat is given forth, and the temperature of surrounding objects rises. 4. Mechanical compression raises, and mechanical expansion diminishes the temperature of all bodies, solid, liquid and gas- eous. EXPERIMENTS. 231 5. If the result of. mixing two liquids be, that they occupy- less space than before, heat is produced. Four parts, by weight, of sulphuric acid, and one part, by weight, of water, become condensed when mingled, and sufficient latent heat is set free to heat the mixture above the boiling point of water. 6. If the result of mixing two liquids be, the production of a solid, great heat is produced. One or two drops of sulphu-ic acid added to a solution of chloride of calcium, produces a solid, and gives forth a large amount of heat. 7. If a solid be dissolved in water, cold results. Nitrate of ammonia thrown into water will be at once dissolved, and great reduction of temperature will take place. 8. If a liquid be added to a solid, and be at once absorbed, heat results. If quicklime be thrown into water, the water disappears, and great heat is produced, sufficient to inflame matches, and set fire to buildings and vessels. Many other phenomena of daily occurrence in nature and the arts may be explained on these principles. Experiments: Specific Heat, k 1. Specific Heat. To show that equal amounts of heat, added to different sub- stances, increase their temperatures unequally, or that their capacities for heat are dif- ferent, mix 1 Ib. of water at 100, with 1 Ib of mercury at 40 : the temperature of the mixture will be 98. Then mix 1 Ib. of mercury at 100, with 1 Ib. of water at 40, and the temperature of the mixture will be 42 only. The same amount of heat has been added in both cases Why this difference of result? Because the water has a greater capacity for heat than mercury. 2. Heat balls of zinc, copper, tin, iron, lead, of the same weight, to the same degree, by immersing them in boiling water, and then dip them all into different vessels, of the same size, all containing equal weights of water at 32, each having a thermometer in it, and note the different heights at which the thermometers stand at the end of half an hour. 3. This experiment may be varied by observing the times occupied by the different metals in raising the temperature of the different vessels of water to the same degree. 4-. Observe the amount of ice melted, and water formed, by the cooling of equal weights of different substances. This is the most satisfactory mode of ascertaining spe- cific heat. 1. Change of State produces change of Temperature. Mix equal parts of snow and salt together ; great cold results from their liquefaction. 2. Add a few drops of sulphuric acid to a strong solution of chlorohydrate of lime, (muriate of lime);a solid results, and great heat is produced. 3. Add water to quicklime ; a solid results, and great heat is produced. 4. Potassium and sodium pressed together in a mortar, produce a liquid alloy ; add mercury, and this liquid solidifies, and heat enough is produced to inflame the naphtha adhering to the potassium. 5. Hammer iron, and it becomes very hot. 6. Compress water by a powerful screw, and the thermometer rises ; remove the pressure, and it sinks. 7. Compress air in the fire syringe, and a piece of well dried punk, or tinder, will be inflame!. 8. Exhaust the air from a bell glass, by the air pump, and the thermometer will sink ; allow the air to enter again, which is the same thing as compressing it, and the ther- mometer will rise. 9. Mix equal volumes of sulphuric acid and water; an increase of density results, with grat rise of temperature. 232 THE SOURCES OF HEAT. 10. Mix equal volumes of alcohol and water; condensation results, and rise of tem perafcure. VII. The Sources of Heat. 247. The Sources of Heat. The sources of heat are nu- merous, but they may all be reduced to seven; viz: 1st, The Sun. 2d, The internal heat of the earth. 3d, Chemical action and combustion. 4th, Electricity. 5th, The absorption of moisture. 6th, Vital action. 7th, Mechanical action. 248. The Sun. Of all the sources of heat, the, sun is the most intense. The cause of the sun's heat is unknown, but it is probably due to electrical or chemical action. The amount of heat which the earth receives from this source is enormous. Faraday has calculated that the average amount radiated by the sun upon an acre of land, on a summer's day, is equal to that which would be produced by the combustion of sixty sacks of coal. It has been estimated that the amount of solar heat entering the atmosphere of the earth in one year, is sufficient to melt a layer of ice completely enveloping it, from 90 to 100 feet in thickness ; of this amount however, the earth only re- ceives about two thirds, the rest being absorbed by the atmos- phere. This vast amount is, however, but a small part of that radiated by the sun ; calculating the area which the earth pre- sents, and its mean distance from the sun, it has been found that the earth does not receive at any moment, more than 5"!TT<5Wo o otion? On the other hand is motion the sole cause of heat, according to the mechanical theory ? What proportion exists between the heat produced by a definite amount of mechanical motion and the motion produced by the same amount of heat ? 240 SATISFACTORILY EXPLAINS gree, heat is the result. Consequently, mechanical motion is spoken of as the cause of heat, by which is meant, that it is the sole cause, while heat, on the other hand, is never spoken of in this sense, as the sole cause of motion. 260. The amount of Heat produced by a definite amount of mechanical motion, and the Mechanical Klotion produced by the same amount of heat, are precisely equal. It has been shown that the amount of force produced by the fall of 772 Ibs. through 1 foot, is sufficient to raise the temperature of 1 Ib. of water 1 F. i. e., this is the amount of heat which would be generated if a 772 Ib. weight, after having fallen through 1 foot, had its moving force destroyed by collision with the earth. Conversely, it has been shown, that if the force produced by a"n amount of heat which would elevate the tem- perature of 1 Ib. of water 1 were all concentrated, it would be sufficient to raise 772 Ibs. 1 foot into the air. From these facts we draw the conclusion that the heat produced by motion, and the motion produced by heat, are not simply accidental circumstances, but, that there is, in these cases, a certain definite amount of mechanical motion converted into the motion which we call heat, which ceases to appear any more as mechanical motion ; and on*the other hand, a certain definite amount of heat motion converted into mechanical motion, and which ceases to appear any more as heat. These forces are not lost or de- stroyed, but merely converted from one kind of force into the other, and may be recovered again by the contrary conversion. It follows from this, that, in all cases where heat is used to pro- duce motion, as in the case of the steam engine, an amount of heat disappears or is used up proportionate to the mechanical effect produced. It is believed that the heat possessed by the s -earn when it enters the cylinder of the high pressure steam engine, is not all found in the steam which issues from the same cylinder, after the piston has been moved, but that a portion of this heat has been consumed and converted into mechanical motion, and that this mechanical motion in spending itself, has produced again an equal amount of heat, by friction, in the vari- ous parts of the machine. According to the material theory of heat, none of the heat of the steam, which is used, is consumed, 230. What is the amount of mechanical motion produced by the heat necessary to raise 1 Ih. of water 1? Conversely, what is the heat produced by the mechanical force, necessary to raise 772 Ibs. 1 foot? When heat is used to produce motion, does tha whole of the heat appear at the conclusion of the process, or htis a part been consumed in producing the motion? Illustrate this iu the case of the steam engine. Is the heat which exists in the steam when ic enters the cylinder of a high pressure engine all found iu. it when it leaves the cylinder ? If not, what has become of it I MANY COMMON PHENOMENA. 241 but the whole is found in the steam which issues from the cylin- der, and may be collected in the condenser. The mechanical motion, according to this view, is not due to the conversion of heat into motion, but merely to its expansive effect in passing from the boiler to the condenser. 261. Some of the common phenomena of heat explained upon the mechanical Theory. According to this theory, the particles of bodies being in a state of incessant vibration, heat is supposed to be produced by increase in the intensity of the motion. When the atoms move beyond a certain determined velocity, and the vibrations become more extended, the heat evolved pushes the particles apart and separates them from each other, thus causing the body in question to increase in volume, and producing expan- sion. When the vibrations of the particles become sufficiently extensive, they are then loosened from each other to such a de- gree as to be able freely to interchange places, and liquefaction is the result. When the vibrations are pushed so far that the par- ticles are separated too far from each other for cohesion to bind them together, they become self-repellent arid elastic, and the vaporous state is produced. When a hot body, whose particles are in a state of vibration, is brought near to another, colder than itself, the vibration is communicated to the particles of the second body, which are thus, in their turn, set in motion, or conduction takes place. When heat is radiated it is supposed that the oscillating motion of the particles of the hot body is communicated to the particles of a very fine and delicate ether pervading all space, which, as soon as they begin to vibrate, produce a succession of undulations, that are propagated in ri.irht lines until they reach some material obstacle, to the par- ticles of which their motion is then communicated. This is supposed to be the mode in which radiant heat is propagated through spacer and made to affect the temperature of bodies on which it falls. When a solid body is liquefied, it is well known that a large amount of heat becomes latent, which, it has been thought, combines with the solid, in order to form the liquid. According to the mechanical theory, this heat is not stored or combined, but has been simply expended or used up in forcing the particles of the body apart, i. e., in the production of a certain amount of motion, and when these particles approach each other 2st substances may thus be made to emit light of the greatest brilliancy and inten- sity. From this it would seem that Light is only the exceed- Show how the diminution of temperature in the atmosphere, as we ascend, may be ex- plained upo.i the mechanical theory. 263. Show how heat can be converted into light 244 TH2 CONVERTIBILITY OF FORCES __.,,< ingly rapid vibrations of the same ether, which when vibrating more slowly produces merely the effect and sensation of Heat. As the^e heat vibrations increase in rapidity they produce, first that kind of light which results from the slowest Light vibrations, then that color which is produced by vibrations of a more rapid character, and finally blue light, which has been found to be produced by the most rapid vibrations, and to be possessed of the greatest refrangibility. On the other hand, that Light may be converted into Heat, seems to be proved by the experiment of placing cloths of different colors upon the snow. The temperature of these cloths is shown by the depth to which the snow is melted beneath them; and this is found to be precisely the order in which -they absorb the light: blade de- stroys all light vibrations and it is found to be healed the most and sunk the most deeply in the snow; next comes blue, gr^en, purple, red and yellow, white reflects all the liglit, and conse- quently is hca'ed the least of all the colors. Light can also be resolved into heat through the medium of chemical action. Heat and Light are therefore produced by the same cause, act- ing with different degrees of intensity, and we naturally pass, therefore, from the study of radiant Heat to that of radiant Light. 261. The convertibility of the Forces which act upon mat- ter into each other and their indestructibility. The general conclusion at which modern science has arrived, is that the va- rious forms of force which act upon matter are, many of them, if not all, capable of passing into each other, and that in all cases when a force seems to be destroyed, it is not really so, but simply converted into another variety of force of equal energy. Force is, then, believed to be as indestructible as matter. By this expression it is not meant that either force or matter are incapable of destruction, but simply, that in fact, as the material world is at present constituted, neither of them is destroyed in the various transmutations which they undergo, but are merely changed from one form to another. The pri- mary form of force which is selected as the type of all the oth- ers is mechanical motion. Into this all the others are capab'e of being resolved, and out of it, most of them can be again el' cited. From heat may be obtained light, electricity, chemi- cal action and motion; from light may be obtained chemical Show that light may be converted into heat 254. What is the general concluFion of modern science in regard to the convertibility of the forces that act on mutter, aiii t-ieir indes tr uctibility . WHICH ACT UPON MATTER. 245 action and heat; from electricity, heat, light, chemical action, and motion ; from chemical action, heat, light, electricity, and motion ; from motion itself, heat, light, electricity, and chemical action. The intimate connection of Heat and Light, c.nd their mutual convertibility, will be seen more clearly from the follow- ing chapter. 264*. There is an Analogy between Sound, and Heat, and Light. It is well known that sound is produced by vibrations imparted to the air, and that the pitch of a sound depends upon the number of these vibrations. In like manner it is thought that heat and light are produced by the vibrations of an ex- tremely sensitive ether with which all matter is peimeated. 1 he difference between the vibrations of air and ether consists in the greater delicacy and elasticity of ether, which not only admits of a greater rapidity in the propagation of motion, but also of an immensely greater number of vibrations per second, \\ hich require to be counted by billions. The difference there- fore between sound, heat, and light is chiefly a difference in the rale of vibration of the respective media which produce them. Again, the vibrations communicated to air are also imparted to the ether by which it is permeated. These vibrations at first produce only the phenomena of sound, but as soon as they exceed a certain number per second the phenomena of heat begin to manife t themselves, and should these vibrations go beyond a certain limit, then the phenomena of light make their appear- ance. Here we have another illustration of the convertibility of forces, which is described very elegantly by Dove as follows : " In the middle of a large darkened room let us suppose a rod set in vibiatiou and connected with a contrivance for continu- ally augmenting the speed of its vibrations. I enter the room at the moment when the rod is vibrating four times in a second. Neither eye nor ear tell me of the presence of the rod, o.Jy the hand which feels the strokes when brought within their reach. The vibrations become more rapid, till when they reach the number of thirty-two in a second, a deep hum strikes my e;ir. The tor.e rises continually in pitch, and passes through all the intervening grades up to the highest, the shrillest note, then ail j-inks again into the former grave-like silence. "While full of astonishment at what I have heard, I feel suddenly (by the in- creased velocity of the vibrating rod) an agreeable warmth, ag from a fire, diffusing itself from the spot whence the sound had proceeded. S.ill all is dark. The vibrations increase in ra.- 246 THE NATURE OF LIGHT. pidity, and a faint red light begins to glimmer ; it 'gradually brightens till the rod assumes a vivid red glow, then it turns to yellow, and changes through the whole range of colors up to violet, when all again is swallowed up in night. Thus na- lure speaks to the different senses in succession, at first a gentle word, audible only in immediate proximity, then a louder call from an ever increa-ing distance, till finally her voice is borne on the wings of light from regions of immeasurable space." CHAPTER III. THE SECOND CHEMICAL AGENT: LIGHT. THE NATURE OF LIGHT; SOURCES; REFLECTION; REFRACTION; SOLAR SPEC- TRUM; SPECTRUM ANALYSIS', EFFECT OF LIGHT ON PLANTS; CHEMICAL EFFECTS OF LIGHT} PHOTOGRAPHY; RELATIONS OF LIGHT AND HEAT. 263. The nature of Light, The second of the great Im- ponderable Agents controlling the action of Affinity, and play- ing an important part in many chemical phenomena, is Light. There are two hypotheses in regard to the nature of light cor- responding with those which have been explained in regard to the nature of heat. According to the first of these, light is a subtile material fluid, which is thrown off by all luminous bodies, composed of particles inconceivably minute, and moving with immense velocity. These particles falling on different substan- ces are reflected, transmitted, or absorbed, and when they strike upon the optic nerve, produce the sensation of light. The second hypothesis supposes that light is the result of undu- lation, produced in an exceedingly rare and subtile medium, pervading all space, and filling the interstices of all forms of mat er. This medium is not light itself, but it can be thrown into the vibrations which constitute light by impulses communi- cated to it by all luminous objects. The latter is the theory now generally received, as it affords the most complete explana- tion of all the phenomena of light. It is strongly supported by 'the analogy of sound, which, as is well known, is produced by the undulations of the air, and is in like manner susceptible of transmission, reflection, and absorption ; it also corresponds with 235. What Is the second imponderable ? IIow many theories are there in regard to the ature of light ? State the material theory. The undulatory theory. SOURCES OF LIGHT. THE SUN. 247 .the undulatory theory of heat already explained, and now be- ginning to be generally received. 265. The sources of liight.-Solar Xtigiit. The first and most important source of light, is the sun and the heavenly bodies. The origin of the light of the sun and the stars isjm- known, but it is generally supposed that the inflammable mat- ter which appears to surround the sun is gaseous in its charac- ter, because the light which it emits is the same as that which proceeds from gaseous, inflammable substances, and does not afford any trace of polarization by the instruments intended to detect it. Astronomical investigations have rendered it proba- ble that the sun consists of two parts, a central mass, emilting light of great brilliancy, and an external luminous atmosphere, also emitting light, and called a photosphere. This view of the constitution of the sun is supported by the recent discoveries con lected with spectrum analysis. 267. Ignition of Solids a source of Light. Whenever any solid body is raised to a temperature of 900, or 1000, it be- gins to emit light, and becomes luminous, or incandescent. Even gaseous matter, if heated to 2000, becomes feebly lumi- nous. , If any solid matter be introduced into a current of gas at this high temperature, the brightness of the light is greatly increased, and it is upon the ignition of solid matter in the interior of currents of intensely heated gas, that all processes of artificial illumination in common use, depend. In the case of ilLnninating ga^, kerosene, candles, and oil, the solid sub- stance emitting the light, is carbon in a state of intense igni- tion, precipitated from the gas in which it previously existed in combination with hydrogen. This very curious and beautiful process, on which so much of the comfort and enjoyment of man depend^, will be more particularly described hereafter, One of the most remarkable in-tances of the production of light in this manner is seen in the case of the Drummond light, in which a jet of mixed oxygen and hydrogen is directed upon a pi; ce of solid lime. The gases burning alone produce a flame which is hardly perceptible, but the moment the lime is introduced, the brilliancy of the light becomes at once too great for the eye to bear. Even a piece of platinum, or of china, introduced into 2-58, What is the first source of light ? Why is the light of the sun and stars supposed to be of g iseous origin ? What is supposed to bo the constitution of the sun ,'267, \Vu.it is the second source of light ? How can solid matter be mado to emit light ? On what do all processes of artificial light in common u'e depend? What is the ignited solid sub- Btance which, emits light in the burning of i.luminating gas and candles? Explain tUt) Drummond light. Does the ignited solid in tills c.^o undergo aay change? 248 IGNITION OF SOLIDS. ELECTRICITY. this flame, or any other solid substance, will instantly begin to emit light. In all these cases the solid itself undergoes no change, and remains unconsumed. The color of the light va- ries with the intensity of the heat ; when first perceptible, it is of a dull red, and gradually passes into orange, yeilow, white, and violet. The temperature at which bodies begin to emit red light in the dark, is about 700, but in broad daylight, solid matter does not become incandescent until heated to 1000. Platinum begins to emit light in the dark, at 977. If platinum, brass, antimony, gas-carbon, porcelain, black-lead, copper, and palladium, be introduced into a clean gun-barrel, which is then raised to a dull red heat, they are found, on looking into the barrel, to emit red light at the same moment, showing that they all require nearly the same temperature to make them incan- descent. Chalk and marble, under the same circumstance-, require a lower temperature, and begin to emit light before the gun-barrel is red-hot. 268. Electricity a source of Light. This is a powerful source of light, as may be seen in the case of the sparks pro- duced by the ord'nary electric machine, and also by the excess- ive brightness of a flash of lightning. The galvanic battery produces a steady and permanent light, too bright for the un- protected eye to bear, if the wires from the two poles are tipped with charcoal, and brought near enough to each other for the electric current to pass. Attempts have been made to employ this light in light-houses, but with indifferent success. In the galvanic battery, chemical action is the source of the electrical current ; but this may also be produced by the revolution of wound armatures before the poles of powerful magnets, and if this current be allowed to pass through charcoal points, light of equal in-ensity to that of the galvanic battery may be obtained. The motion required may be generated by a small steam engine. This is the form in which electricity is now chiefly used for the production of artificial light. Here we have a striking instance of the conversion of forces ; heat produces motion ; motion is resolved into electricity, and this electricity into heat and light. The electric light from the battery is frequently substituted for the sun, in optical experiments, on account of its excessive brightness. What is the temperature at which red light in the dark is emitted ? In broad day- light ? Do all bodies require nearly the same temperature to render them incandescent? 268. What is the third source of light ? What is said of the light produced by the galvanic battery? To what purpose has it been applied? By what other means has light of equal intensity been produced ? Can motion be converted into light ? What r illustration does this afford of the conversion of forces ? PHOSPHORESCENCE. CRYSTALLIZATION. 249 269- Exposure to the sun's rays, and to electricity, a source of Slight. There are some substances, like the diamond, and other minerals, which, after being exposed to the sun's rays for some time, appear luminous when carried into a dark place. Thi> property of emitting light without the application of an eleva'ed artificial temperature, is called phosphorescence. Fluor spar, the diamond, and white marble, acquire phosphorescence, on the discharge through them of a succession of electric sparks. Ag;iin, if fluor spar be heated quite hot, it will become phos- phorescent, and emit a beautiful blue light. 270. Decaying- animal and vegetable matter a source of Light. Sea fish, and especially the herring and mackerel, become phosphorescent shortly after death. By placing such fish in weak saline solutions, such as sea salt, these solutions become lumi- nous, and this appearance will continue for some time. In like manner, certain species of wood, in a state of decomposition, become phosphorescent, and shine with considerable brilliancy in the dark. In all these cases the light ceases to be given forth if the temperature be reduced below 32. The light is probably due to a species of slow combustion, produced by the combination of the substance in question with the oxygen of the air. Phosphorus, a simple sub. tance extracted from bones, also emits quite a brilliant light, when exposed to the air, on account of its rapid union with oxygen, and as this substance exists to a limited degree in all animal and vegetable matter, it is. not unlikely that their phosphorescence may be due to this cause. 271. Luminous animals a source of Ztight. The glow-worm and the fire-fly have the power of giving out light, and in tropical climates there are numerous insects which, on being irritated, emit sufficient light to allow of reading. The waters of the ocean, in tropical latitudes, emit a beautiful phosphorescent light, on ag'tation, which is thought to be due to the presence of minute animalcule-. Two of these animalcules placed in a bottle of water, have been known to diffuse a luminous influence through the whole mass. 272. Crystallization a source of Idg-ht. If sulphate of sod i, and a few other salts that have been fused by the action of fire, be dissolved in water, and crystallized, the formation 2 "9. What is the fourth source of light? What is phosphorescence? How do fluor spiv, tlie di.m.ond, and white marble, acquire phosphorescence ? 270. What is the fifth sou re e of lies may be horizontal, as at A, Fig. 103, and allowing a beam of sunlight, admitted through a very small circular aperture, to fall at an oblique' angle upon one of the other fares, the beam of sunlight, in passing through the prism, will be re- fracted twice, once at its entrance, and again at its emerg- Wiiat e!Tect takes place when polarized light is transmitted through bodies whoso struc- ture is not perfectly homogeneous? What applications have been made of thefe prin- ciples? 276. How can the compound nature of solar light be shown? In what respects do th different kin. Is of lig'it differ f'-om each other? Who discovered the compound nature cf lijjht? What is. a prism ? IIow can it Le use<4 to decompose light? '254 BY THE The Decomposition of Light. Fi S- 103 - ence from the prism, and 1 he rays of which it is com- posed being bent from their original course unequally, will be separated from each other, and caused to di- verge. In corse- qUCIlCC of this di- vergence, the dif- ferently colored rays will become distinct, and be beauti- fully displayed if a screen be placed to receive lh< m. The colored rays are seven in number, and are always arranged in the same order. The oblong spot of colored light which they form is called the solar spectrum. At the upper end of the spectrum, where the most refracted rays fall, the color is violet ; then comes the indigo ray, the blue, green, yellow, orange, and red, which is refracted the least. The shape of the spectnm depends upon the shape of the aperture ; if this be circular, th spectrum will be bounded laterally by vertical straight lines, and at the ends by semicircles ; its breadth is always equal to the diameter of the aperture ; its length varies with the refract- ing angle of the prism, and the substance of which it is made. As in the original beam of white light, the various colored rays are all superimposed, it follows that if the spectrum formed be only slightly elongated, in consequence of the feeble refractive power of the prism, the different colors will overlap each other, be more or less blended, and none of them will present a clear and decided tint. In order to increase the brilliancy of the spectrum, it is necessary that the aperture through \\hich the light is admitted should be very small, in order to obtain the finest possible beam of light, and then that the screen should le p'aced at a considerable distance from the prism, so that the rays may not strike it until they have widely diverged, and be- come completely separated from each other ; in this manner a spectrum may be obtained in which the different rays will dis- play clear and decided tints of great brilliancy and beauty. The most effective mode of producing this result is to form a Describe the so!ar spectrum. What is its shape? How can it be displayed to the best advantage? How may the brilliant line of colored light produced by this means be widened ? THE SOLAR SPECTRUM. 255 minute image of the sun by means of a convex lens, and allow the light which proceeds from it to fall upon a screen, pierced with a very small aperture. The light which passes through this aperture may be considered as emanating nearly from a physical point, and the overlapping of the different colors is almost entirely prevented. Another cause of the imperfect separation of the different rays exists in the prism itself. Ordi- nary prisms are full of striae, by which the light is irregularly refracted, and the different colors intermingled. This difficulty may be overcome to a certain extent by transmitting the rays as near the edge as possible. The effect of this reduclion in the diameter of the aperture will be to diminish the width of the spectrum, and reduce it to the form of a mere line of light of the most brilliant colors. In order to give breadth to this line it is necessary to convert the circular aperture into an ex- tremely narrow slit, formed by perfectly parallel knife edgas, only a very small fraction of an inch apart ; a spectrum will thus be formed, horizontal and rectangular, having its upper edges, as well as its sides, parallel. This arrangement is the one best adapted for making accurate observations upon the spectrum. The colored spaces do not occupy an equal extent in the spectrum ; the violet is the most extended, and the orange the least ; if the prism be of flint glass, and the spectrum be divided into three hundred and sixty equal parts, it is found tint the red rays occupy forty-five of these parts, the orange twenty-seven, the yellow forty-eight, the green sixty, the indigo forty, and the violet eighty. If the screen on which the spec- trum is formed be perforated opposite any of the colors, as the violet, for example, a small beam of pure violet light will pass through, which may be examined separate from the others. If this beam of violet l : ght be allowed to fall on a second prism, and its image received on a second screen, it undergo; -s no decomposition into light of various colors, but simply produces a spot of violet light, of the same shape as the incident bcnim. This beam may be again and a^ain refracted by prism => and leases, but it will undergo no further change. The same i-5 true of all the colors. Hence it appears that the different rays of the spectrum are incapable of further separation in o rays of different colors, by subsequent refraction, and that What will he the shnpe of the spectrum formed by knife edges ? Bo the different colors occupy the same space in the solar spectrum ? What is the proportion? Show that the duU-rent colors are not susceptible of further decomposition. Are the colors confined to one part of the spectrum ? 256 THE HEAT RAYS OF the solar spectrum gives us the ultimate analysis of white light. From these and other experiments, Sir Isaac Newton in erred that white light is composed of seven co'orific rajs; later experiments have led to the opinion that the seven colors of the spectrum are occas : oned not by seven, but by three simple or primary " rays, viz., blue, yellow and red. These rays are concentrated at those points in the spectrum where each of these colors appears the brightest, but each color is in reality spread over the whole spectrum, forming, with the others, a variety of mixtures, red and yellow producing the orange; yellow and blue the green; red ard blue, with a liltle yellow, the violet. The prismatic colors also differ in their illu- minating power ; the orange illuminates in a higher degree than the red, the yellow than the orange. The maximum of illumi- nation lies in the brightest yellow, or the palest green ; tej ond the full deep green, the illuminating power sensibly dimini.-.hes; the blue is nearly equal to the red, the indigo is inferior to lie blue, and the violet is the lowest on the scale. If the ftvcn colors of the spectrum be received upon seven distinct minors, so arranged as to reflect them all to one point, the orig nal white light of the solar beam will be reproduced. 277. The number cf vibrations required to produce t he dif- ferent colors of the solar spectrum. According to the undula- toiy theory of light, the average length of a wave in white light is estimated at S-O^OTT f an mcn 5 m re ^ n g nt > at 34^00 f an inch; in violet, at s^o<7 f an mcn - The nrmber of vibia- t'.ons in white light is estimated at 500,000,000,000,000 per second; in red light, at 482,000,000,000,000; and in viokt light, at 707,000,000,000,000. 278. The heat rays of the solar beam. Besides the different kinds of light of which the sunbeam consists, it also contains rays of heat, and heat of different kinds. The.^e rays of heat are distributed through the spectrum, and are not com entiat< d at one point ; consequently, they possess different refrangibili- ties, and are distinguished from each other by this property. If these rays of heat were exactly similar, they would be equal in refrangibility, and be all collected at one point, after passing through the prism. They not only differ in refrangibility, but also in heating intensity, in the same manner as the rays of According to later experiments, of how many colors is the solar spectrum thought to consist? Where is the point of maximum illumination situated? 277. What is the length of a wave in white light? In red? In violet? What are the num her 'of vi)-ra tioiis in,white light? In red? Tn violet? 278. Show that there are different kinds of rays of heat in the solar beam. THE SOLAR BEAM. 257 lio-ht differ in illuminating power. This fact was first observed by Sir W. Herschel, who observed that in viewing the sun with laro-e telescopes, through differently colored glasses, he some- times felt a strong sensation of heat, with little light ; and at other times he had a strong light, with little heat. His experi- ments were made by transmitting a solar beam through a prism, receiving the spectrum on a table, and placing the bulb of a very delicate thermometer in different parts of if. The thermometer was found to stand at different points in tlie differ- ent rays; thus, if in the blue rays, it marked 56; on moving it down to the yellow rays, the instrument indicated a tempcra- ture of 62 ; while at the lower end of the spectrum, at the extremity of the red rays, the temperature was found to be as high as 79, i. e., 23 higher than in the blue rays. It wa^ also observed that not only the red was the hottest ray, but th:it there was a point a little beyond the red, altogether out of th'3 spectrum, where the thermometer stood higher than in the red it-elf. The mo,-t inten e heat was always beyond the red ray, where there wai no Tght at all, an 1 the heat, in all the ex- periments, was found to diminish progressively, from the red to the violet, where it was least. These invi ible rays of heat were found to exert a very considerable effect at a point 1^ inches below the extreme red ray, even though the thermome- ter was placed at a distance of 52 inches from tho prism. O her experimenters have placed the point of maximum heat within the red rays ; and the point is found to vary with the material of which the prism is made. With a prism of rock salt, Melloni succeeded in separating the point of maximum temperature to a much greater distance from the colored parts of the spectrum linn had previou ly been done. On moving the therino-.Tierer below this point, it was found that the rays of heat extended a considerable distance below the colored parts of the spectrum. The conclusion, therefore, is irresistible, that there are in the solar beam invisible rays of heat, of different refrangibillties, and so much less refrangible than the light that the central ray fills considerably below the lower, or red end of the spectrum. The shape of tho thermal spectrum does not coincide with that of light, but is curiously discontinuous, consisting of several dis- tinct parts, and forming at the lower end three round spots, B, c and D ; see spectrum of heat, Fig. 106. Where is tho point of maximum heat? How was this determined? What effect has the nature of the prism ou the point of maximum heat? What is the shape of tao thermal spectrum ? 258 THE CHEMICAL RAYS. 279. The chemical rays of the solar beam. It has long been known that the light of the sun possesses extraordinary chemical power; the di-chloride of mercury, or calomel, and the chloride of silver, commonly called lunar caustic, are black- ened ; transparent phosphorus becomes opaque ; and the color- ing principles of vegetable origin are destroyed, by its action. Solar light will also produce the instantaneous combination of the two gases, chlorine and hydrogen. On the other hand, it confers upon the green cells of the leaves of plants the power of decomposing carbonic acid ; and it has also a wonderful influ- ence in producing the green cells of plants. This chemical energy is not concentrated at any one point in the spectrum, but is extended through several of the colored rays, and outside of them above the violet ; whence we conclude that there are dif- ferent kinds of chemical rays in the solar beam, distinguished from each other by a difference in refrangibility, just as there are different kinds of heat, and different kinds of light. The point of maximum chemical effect does not correspond with the maximum point for light, nor with the maximum point for heat, but is found at the violet, or upper end of the spectrum, Fiys. 103 and 104. Scheele noticed that the effect of the violet rays upon the chloride of silver is more perceptible than that of the other rays. Dr. Wollaston ascertained that the greatest effect is produced just outside of the violet rays. The spot next in energy is the violet itself, and the effect gradually diminishes in advanc- ing to the green, beyond which it seems to be wholly wanting. Nitrate of silver placed in the red rays is not blackened at all. The chemical rays are, therefore, more refrangible than tho e of light, in consequence of which they are dispersed over the blue, indigo, and violet spaces, and even extend a considerable distance outside of, and above this end of the spectrum ; they are often called actinic rays. It is also said that other rays have been discovered in the spectrum which do not exercise any chemical action of themselves, but have the property of continuing it when once commenced ; they are thought to ex- tend from the indigo beyond the violet, and are called pho.-phoro- genic rays. They are so named because they are believed to be the rays which are absorbed by the substances called phos- phorescent, already described, and being emitted again when 279, Give some illustrations of the chemical effect of the sun's rays, Is this chemical energy concentrated at one point in the spectrum ? Are there different kinds of chemi- cal rays? In what respect do they duTcr? Where is the point of maximum effect? What are phosphorogenic rays ? What is the shape of tue chemical spectrum ? FLUORESCENCE. ! these bodies are carried into the dark, constitute the phenomena of phosphorescence. Some experiments of Sir John Herschel seem to show that the shape of the chemical spectrum is not the same as that for light, and is also discontinuous, like that of heat, consisting of a broad band between the orange and the yellow, then omitting the yellow, commencing again at the green ray, and continuing far above the upper end of the violet, gradually tapering to a blunted point. See Fig. 106. 280. The range of the chemical rays in the solar spectrum. FluDrercsnce. The invisible rays extend beyond the violet extremity of the spectrum for a distance nearly equal in length to twice that of the luminous portion ; but in the electric light obtained by the ignition of charcoal points, the invisible spec- trum can be traced nearly six times as far; Figs. 104 and 106. On transmitting, however, these invisible rays through certain substances, such as a solution of sulphate of quinine, the de- coction of the bark of the horse chestnut, tincture of chlorophyll, &c., the rays become visible in consequence of a diminution of their refrangibility. Thus, if a tube, filled with a solution of sulphate of quinine, be placed in the invisible rays, entirely outside of the spectrum, and above the violet ray, a ghostlike gleam of blue light will shoot directly through the tube, and on examining the blue light thus obtained, it is found to contain rays of much less refrangibility than the violet, and not much exceeding tho>e of the green ray. The explanation of this singular effect is, that the invisible rays have had their refrangi- bility reduced by passing through the quinine, and on emerg- ence, possess the refrangibility, color, and other properties of the colored rays of the upper part of the spectrum ; in other words, the invisible rays have been absorbed and re-radiated in a condition of lower refrangibility, such as ordinarily pro- duces the impression of blue light. According to the undula- tory theory of light, the rate of undulation, or the number of vibrations per second which produces the invisible rays, is reduced by transmission through the sulphate of quinine, aid when they issue again, they possess only the number of vibrations which produces blue light. This change of re- frangibility is not limited to the invisible rays outside the lumi- nous spectrum, but can be accomplished also in the case of the visible and colored rays. In every case, the altered rays are 230. How far do the chemical rays extend ahovo the violet ? What is the effect of a solution of quinine on the invisible chemical rays? Explain fluorescence, SUto what w meant by the degradation of H^ht? 11* 2GO TRIPLE CHARACTER OF SOLAR LIGHT. changed into those which are less refrangible, and the change is never to rays of greater refrangibility. This singular change of refrangibility has received the name of the degradation of light, and is analogous to the change of refrangibility produced in rays of heat when they are absorbed by certain substances, constituting another point of resemblance between these two chemical agents. Bodies which have the power of effecting it are called fluorescent, from fluor spar. 281. The triple character of solar light. A beam of s^ar light is therefore composed of three distinct sorts of rays, viz., the heating, the illuminating, and the chemical, and hence is capable of producing three different kinds of effects : fii st, the effect of heat ; second, that of light ; third, that of chemical in- fluence. In a beam of natural sunlight, the different rays are, as it were, intertwined, like the triple strands of a cord, and their influence is exerted at one and the same spot ; but if transmit- ted through a prism, they are separated, in consequence of the difference in their refrangibility, and their maximum influence is manifested at three distinct points. This is clearly ehown in Fig. 104, in which the ray of sunlight, a, by the refraction of the prism, is elongated ?o as to extend from c to b. The rays of heat being less refrangible than those of light, exhibit their maximum effect at H, below the red rays, while, however, their general influence extends from b to v, or to the up- per end of the illumina- ting rays. The ch( mical rays, on the other hand, being more refrangil le than those of light, exhibit their maximum effect at c, a point considerably above the most refrangible of the illuminating rays, while their general influence extends from c to R. The illuminating rays extend from v to R, and the maximum effect Fig. 104. Unequal refransibiliti/ of the Chemical, Illumina- ting and Heating Rays in the Solar Beam. 281. Provo the triple character of solar light. Why are the foci of a lens for light, .beat, and chemical effect, not found at the same point 1 DISSECTION OF 2G1 Fig. 105. i 3 exerted at Y, while, within the same limits, a certain amount of heating and chemical influence is also displayed. From this, it is evident, that the solar beam is possessed of a triple nature, and exerts, wherever it falls, three distinct sorts of influence. On account of the different refrangibility of these three sorts of rays, if a beam of solar light be trans- mitted through a lens, they will not all be concentrated at the same focus, the chemical rays being the most refrangible, will have their focus at a point c, nearer the lens than the focus for light, L, while the rays of heat will be collected at the point H, more remote from the lens than the focus for light ; Fig. 105. It follows from this, that, if the greatest chemical effect of the sun's rays be desired, the object must be placed, not in the illuminating focus, but a little nearer to the lens ; if the greatest heating effect of the sun's rays be sought, the object must be placed a little far- ther from the lens than the focus for light. In order to form a correct idea of the solar spectrum, it is necessary, also, to bear in mind that the different spectra are not all continuous, nor possessed of the same shape. In Fig. 106, this disconti- nuity, as well as the relative extent of the different spectra, and the points of maximum intensity, are well represented, together with the fixed dark lines crossing the spectrum at right angles, which are presently to be described. It will be observed that in the spectrum for light, the maximum point of illumination is in the yellow ray, and that the fluorescent rays extend a con- siderable distance above the upper end of the violet ray. In the spectrum for heat, the shape is peculiar, and the effect at the lower part limited to the four round spaces, A B c D while 'the point of maximum intensity is considerably below the yel- low, at the extreme end of the red ray. In the spectrum of chemical rays, the point of maximum intensity is outside the violet ray, and the continuity of the spectrum is also broken. In the case of Praunhofer's lines, it will be noticed that they have been traced a considerable distance outside of the illumi- nating rays of the spectrum, in both directions, above the vio- let, and below the red. In the spectrum formed by the solar beam, these spectra are not separated from each other, as in the What is their position in reference to the lens? Describe Fig. 106. 2C2 TIIZ SUNBZAM:. Chem. Hays Fi - 10G ' figure, but are superim- posed ; and in the case of any unrefracted solar beam passing through a circular aperture, into a darkened room, are all intertwined, and concen- trated in the small round spot of light produced. 282. The spectra f reduced by artificial ight and colored flames. If artificial light, emanating from different luminous bod- ies, be transmitted through a prism, it is decomposed in the same manner as the solar beam, and a spectrum is formed, consisting of the various colors which pro- duce white light, but never in the same rela- tive intensity and pro- portions in which they The Light. Heat, and Chemical Rays, and the Dark a PP ear hl the eolar S P eC ' Lines of the Solar Beam. triim. The Color which predominates in the artificial light, predominates in its spectrum ; a red flame pro- duces a spectrum in which the prevailing hue is red ; a blue flame a spectrum in which it is blue. If the flame be a pure red or blue, the spectrum will present a continuous band of a red or blue color. There is no artificial light which is not defi- cient in some of the elements of solar light. Colored artificial flames may be produced by placing the salts of different metals in the flame of an alcohol lamp, or gas burner, and the peculiar colors imparted have long been used by chemists as indications of the presence of these metals ; thus a yellow flame is caused by the salts of sodium ; a violet flame is produced by those of potassium ; lithium and strontium salts give a red flame, and 282. Can artificial light be decomposed? Does the spectrum formed differ from that of the sun ? Can metals be detected by the color they impart to flames ? THE SOLAR SPECTRUM 2G3 .Fig. 107. the salts of barium tinge the flame green. The value of these colored flames, as a means of detecting the metals, is diminished when several of these metals are present at once, because the color produced by one melal obscures that produced by another, though this difficulty may be in part removed by the use of colored glasses, or liquids, through which the flame is observed. If, however, these colored flames be subjected to the action of a prism, and the spectrum formed be examined by a powerful telescope, certain characteristic pecu- liarities may be observed which make this the most delicate means of qualitative analysis yet discovered. 283. The solar spectrum not continuous, but crossed by fixed dark lines. Fraunhofer s lines* The solar spectrum not only contains heating and chemical, as well as illuminating rays, but also exhibits, when carefully exam- ined, a great number of dark lines, crossing the spectrum at right angles to the order of the colors, and always occupying the same relative positions. In other words, the solar spectrum is not continuous, but is separated into a great number of portions, of unequal size, by dark lines of division, in which there is no light. That these dark lines indicate the absence of light, is shown by their want of blackening effect, and their correspondence with the inactive spaces which are observed when a photograph is taken of the solar spectrum. These lines were first noticed by Dr. Wollaston, in 1802, on transmitting solar light through a very nar- row slit, and viewing it directly by the eye placed immediately behind the prism. In 1815, Fraunhofer, a distinguished optician, of Munich, examined the solar spectrum thus produced by a lens, and ascertained the existence of nearly 600 dark lines ; of these he published an accu- rate map, selecting seven, on account of their distinctness, and the ease with which they may be recognized, and distinguishing 283. By what is the continuity of the solar spectrum broken ? Describe Fraunhofer'3 lines. Do they extend beyond the limits of the visible spectrum ? 204 CROSSED BY DARK LINES. Fig. 108. them by the letters B, c, D, E, F, G and H. They have, since his time, been ascertained not to be confined to the colored parts of the spectrum, but to extend beyond the violet ray, and through the whole of the space occupied by the chemical rays. These lines are represented in Fig. 107, and are known by the name of Fraunhofer's lines. B is in the red space, near its ouler end ; c which is broad and black, is beyond the middle of the red ; D is in the orange and is a strong double line, the two lines being nearly of the ssime size and separated by a bright one ; E is in the green, and consists of sev- eral lines, the middle one being the strongest ; F is in the blue, and is a very strong line ; G is in the indigo, and H in the violet. Between B and c, there are 9 lines ; between c and D, there are 30 ; between D and E, there are 84 ; between E and F, 56 ; between F and G, 185 ; and between G and H, 190. In order to observe them, the sun's light must be admit- ted through a narrow, vertical slit, o, into a darkened room, and allowed to fall upon a prism, jo, placed with its axis parallel to the slit, Fig. 108, and at a distance of about 24 feet from it. The prism is fixed before the object- glass of a telescope, /, in such a position that the angle formed by the incident ray with the first face of the prism, is equal to that formed by the refracted ray with the second face ; eo that the position of tli prism is that in which the light is subjected to the minimum amount of di.-persion. These lines are always found, whatever be the solid or liquid medium u?ed in the construction of the prism, and whether its refracting angle be great or email, and under all circumstances they always preserve exactly the same rela- tive position in the respective colored spaces in which they occur. The line B, for instance, is always found at the same relative Instrument for vif icing Fraun- hofer">s Lines. How can these lines be best observed? What is their number? How can they be Jis- lyaed upon a screen 1 ? -- ^ _. THE SPECTRA OF ARTIFICIAL LIGHT 265 distance from the extremity of the red space in the spectrum, whatever the material of which the prism is made. These lines differ very much in appearance ; some are extremely fine, and are hardly visible ; others are very near each other, an 1 resemble a cloud, rather than distinct lines; and there are some which seem to possess a perceptible breadth. Fraua- hofer counted 590 lines; but Sir D. Brewster has since ex- tended the number to 2000. These lines indicate the absence in the solar beam of rays of certain refrangibilities, and the reason that they do not appear in the spectrum as ordinarily formed, is the superposition of spectra, which, in the more per- fect spectrum of Fraunhofer, does not exist. The greater the elongation of the spectrum, and the more widely the colored spaces are separated, the more distinct do these lines become. If it be desired to throw the spectrum upon a screen, it may be done by the arrangement Fi "' 109< shown in Fig. 10,). It has been found that all light proceeding directly from the sun, or indirect- ly from it by reflection, such as the light of the moon and the planets, and the light reflected from Fraunhofer^ Lines displayed vpon a Screen. the cl uds and the Pail1 - bow, gives a spectrum crossed by lines exactly identical. It is a point of great interest to determine the cause of these dark breaks in the continuity of the solar spectrum. The spectra produced by the light of Sirius, Castor, and other fixed stars, are also all crossed by black lines, but different from each other, and from the sun, though in nearly all, some of the most important black lines found in the solar spectrum, are seen. Thus, in Procyon, the double line, D, is found ; and in Capella and Beltegeux, the lines D and b. Arcturus, Aldebaran, p Pegasi, and <5 Virginia are particularly remarkable for the strength and number of the lines by which their spectra are crossed. 284. Spectra produced by the light of the Webulae, and by > artificial light, are crossed by bright, instead of dark, lines< While, however, the spectra of the sun and the fixed stars are found to be crossed by black lines, it is a singular fact that the What kind of lines arc formed in the spectra of the moon, and the planets ? Of the fixed stars ? 284- What kind of lines in the spectra of the Nebula ? Of artificial lights ? 266 CKOSSED BY BRIGHT LINES. spectra of the Nebulas, in the heavens, are crossed by bright, in- stead of dark lines ; and this is also the case with the spectra produced by the various sources of artificial light, by the elec- tric light, by gas, oil, alcohol, and hydrogen. The spectrum of the electric light gives a very bright line in the green ray ; those of hydrogen, alcohol, and oil, give two extremely bright lines in the red and orange. The spectra furnished by colored flames, produced by the introduction of different substances into the flame of an alcohol lamp, give lines of various degrees of color and brightness scattered through the whole spectrum. 285. Spectrum Analysis. These bright lines are simply rays of light of different degrees of refrangibility, and of a color peculiar to itself, emitted by each element, when intensely heated. These rays are mingled with the rays that form the beam of light proceeding from the flame in which the element in question is ignited, and are ordinarily indistinguishable ; but if this beam be passed through a narrow slit and directed upon a prism, the rays of different refrangibility and color are separated fi om each other, and those proceeding from the ignited element make their appear- ance in the form of narrow bright spaces or lines crossing the spectrum at right angles to its length. The examination of the spectra of ignited substances constitutes, therefore, a new method of chemical analysis. All that is necessary is that the substance should be heated to the degree at which it is vaporized, and this vapor made luminous. The light proceeding from an ignited solid body unvaporized like the light of perfectly pure carbon points of the battery, produces only a continuous spectrum, not crossed eiiher by bright or dark spaces. Many of the metals can be made to give their characteristic lines, if heated in the flame of an ordi- nary chemical gas burner ; but most of them require the intense heat of the electric spark, derived either from the galvanic battery, or from Ruhmkorff 's coil, an instrument to be described hereafter. 'I he spark, in passing between two points of the metal in ques- tion, volatilizes a small portion, and heats it so intensely as to enable it to give off its peculiar light. The permanent gases also yield characteristic spectra if a discharge from a powerful Kuhmkorff's coil be passed through them. Thus, if the spark be parsed through an atmosphere of hydrogen, the light emitted is bright red, and its spectrum consists of one bright red, one green, and one blue line, while in nitrogen, the light is purple, 2?5. What effect is produced upon the lines in the spectra of artificial light by ignited nn-tals 1 Is the power of producing characteristic lines in the spectrum confined to the metals? Can the gases be m*de to give characteristic lines? How can we trace the lined beyond the limits of the visible spectrum? SPECTKOI ANALYSIS. 267* and the position of the lines entirely different. When a pound gas, or vapor, is ignited by the electric spark, the spectra produced are those of the elementary components of the gas. At these intense temperatures, chemical combination seems to be impossible, and the various elements are able to coexist in a separate form, mechanically intermingled. If photographs of these spectra be taken, the impression obtained contains all the lines characteristic of the elements in question. The photo- graph being produced by the chemical and extra violet rays, gives a spectrum which extends much beyond the limits of the violet ray, and contains lines not seen when the spectrum is viewed through the telescope; see Fig. 107. The minutest quantities of the different elements, if ignited, will give the characteristic lines with perfect distinctness, and if several ele- ments happen to be contained in the same flame, the lines peculiar to each are as plainly seen as they would have been had no others been present. Sodium gives a single or double line of yellow light in a position corresponding to that of the orange rays in the solar spectrum. Potassium gives a red line in the red end of the spectrum, and a violet line tit the violet end. Lithium gives a dark spectrum, with only two bright lines, one a pale yellow, corresponding to the yellow portion of the spectrum ; the other a bright red, in the red end of the spectrum. Strontium presents eight characteristic bright lines. Calcium gives one broad green band, and one bright orange band, besides several smaller orange lines. Messrs. KirchhofF and Bunsen, to whom we are indebted for the first investigation of this subject, state that the amount of sodium which can 'be detected in this manner need not exceed the 190,000,000th part of a grain ; of lithium, the 70,000,000th part ; of po'as- sium, the 60,000th part of a grain ; bromine the same ; stron- tium, the 1,000,000th; calcium, the 100,000,000th part of a grain. The yellow line of sodium, No. 3, Fig. Ill, is always found, whatever be the kind of light employed. This is owing to the extensive diffusion of this element in the atmosphere, and its presence in every substance which has been exposed to the a'rr for however short a time. Lithium, which was form- erly supposed to be contained in only four minerals, by the aid of spectrum analysis, has been observed in almost all spring waters, in tea, tobacco, milk, and blood, but existing in such St:it<> the characteristic lines of sodium. Potassium. Lithium. Strontium. Calci- um. How minute a quantity of each cau thus be detected? 268 THE SPECTROSCOPE. minute quantities as to have eluded detection by the less deli- cate methods of analysis. 206. The Spectroscope. The instrument used in these re- searches is called the Spectroscope, Fig. 110. It consists of a Fig. 110. The Spectroscope. prism, p, mounted vertically upon a firm iron stand, F, and a tube, A, carrying a lens at the end nearest the prism, and at the other extremity having a very fine vertical slit lor the admission of the light. The width of this slit can be regulated by the small screw, e. The stand, s, carries a sliding rod, which sup- ports the substance to be analyzed, in the flame of the gas burner, E. This burner is placed oppo-ite one half of the slit, and its light passes directly down the tube to the prism ; oppo- site the other half of the slit is placed a small rectangular pri.- m, the object of which is to reflect the light proceeding from some other source, as the sun, or any artificial light, D, al^o down the axis of the tube. By this arrangement, spectra, pro- ceeding from two different sources, are formed, one above the other, and can readily be compared, so as to decide whether 286. Describe the Spectroscope. 287. What new metals have been discovered ? THE SPECTRUM OF THE SUN 269 their lines coincide, or differ. The light having been refracted by the prism, is received by the telescope, B, and the image of the spectrum magnified before reaching the eye. The telescope is movable in a horizontal plane, upon the tripud, and can be adjusted so as to observe every part of the spectrum formed by the prism. The tube, c, contains a lens at the extremity near- est the prism, and at the other, a scale formed by transparent lines on an opaque ground ; this tube is adjusted in such a way that a light being placed at the open extremity, the image of the scale is reflected by the prism into the telescope, B, for the purpose of reading off the position of the bright and dark lines of tha spectrum, as both will appear simultaneously placed side by side in the field of the telescope. When the instrument is used, stray light is excluded by covering it with a loose black clolh. The dispersion of the spectrum may be much increased by using several prisms instead of one. The prism is some- times made hollow, and filled with bi-sulphide of carbon. 237. The new metals discovered by spectrum analysis. In the course of his researches upon the bright lines in the spectra produced by the alkalies, the German chemist, Bunsen, observed several lines which could not have been produced by the:n, and which led him to suspect the existence of a new m 'tal. On evaporating 40 tons of the mineral waters of Durck- hbim and Baden, he obtained 105 grains of the chloride of a new metal, which, on being introduced into the spectroscope, gave two splendid 'violet lines, and is called Caesium, from c(zs>'us, bluish gray. In the waters of Hallein and Gastein, there was discovered another new metal, Rubidium, from rubi~ dus, dark red, because it has two splendid red lines in its spec- trum. A third metal, called Thallium, has since been discov- ered, so called from OuW)^, a budding tivig^ in allusion -to the brilliant green line presented by its spectrum. Indium was recognized by the presence of a hitherto unobserved fine dark blue line. The peculiar appearance of the spectra of several of the metals, as seen through the spectroscope, is represented in Fig. Ill, the dark lines of the solar spectrum being repre- sented in black, the differently colored lines of the other spec- tra in white. No. 1 represents the solar spectrum ; No. 2, that of potassium ; No. 3, that of sodium, its bright line being iden- tical in position with the dark solar line, D ; No, 4, that of the new metal, rubidium ; No. o, that of another new metal, caesium.* The spectra of the same me.als are represented in colors iu the Frontispiece, 270 COMPARED WITH THOSE OF THE METALS. Fig. 111. 1. 2. 3. 4. 5. Solar Spectrum. Potassium. Sodium. Rubidium. Caesium. The dark lines in the Solar Spectrum, compared with the bright lines in the Spectra of Potassium, Sodium, Rubidium and Ccesium, THE DARK LINES OF THE 271 Fig. ill * 288. The dark lines of the solar spectrum exactly coincident with the bright lines of spectra produced by the metals. Kirthhoff', in ex- perimenting on the bright lines found in the spectra produced by the burning metals, discovered that these bright lines are in many cases exactly coincident with the dark lines mapped by Fraun- hof'er, in the solar spectium, so that when the two lights are thrown into the tube through the same slit, and their spectra are seen through the same telescope, B, %'iy. 110, arranged one above the other, the bright lines of the one are found to be continued, without the slightest inter- ruption, into the daik lines of the other. Thus sodium, for example, when ignited, emits an intensely biilliant yellow light, which is concen- trated into two closely con- tiguous bands, or bright lines, coincident in position with Fraunhofer's double black line, D, in the solar spectrum ; it was also found that the bright lines characteristic of potassium, chromium, mag- nesium, iron, and nickel, ex- actly correspond with certain of the black solar spectra lines; vaporized iron gave about 60 bright lines, coincid- ing in position, and in breadth, with the same number of black lines produced, by the sun. In Fig, 11 1*, a representa- tion is given of the coinci- 272 SOLAR dence of more than 60 of the bright lines in the spectrum of Iron, with as many dark lines in the spectrum of the sun. It seems impossible that this should be an accidental coincidence, and it at once sugge?>ted the idea that they are dne to the same cause, and that the dark lines in the solar spectrum are pro- duced by these metals, ignited in the atmosphere of the sun. The only difference is, that in the one case the lines are bright, in the other they are dark. The probability that such a coinci- dence should be a mere chance, instead of really indicating the presence of Iron in the sun's atmosphere is, according to the doctrine of probabilities, only 1 to 1,152,930,000,000,000.000. 289. The bright lines afforded by metallic spectra convert- ed into dark lines. The dark lines of the solar spectrum ex- plained. Now it has been found that the bright lines of the metallic spectra may be converted into black lines, by placing behind the flame in which the metal is ignited another flame, much more intense than the first, and containing the same metal in a state of more intense ignition. For instance, if through the flame of a common alcohol lamp, colored by sodium, the more powerful light of sodium, heated by hydrogen, or by the electric light, be transmitted, the bright lines found in the spec- trum of the first sodium light, are instantly changed into black lines, occupying the same position ; the bright lines in the spectra of potassium, lithium, barium, and strontium, may be converted into black lines, in a similar manner. In other words, if any element be ignited and vaporized at a high temperature, it emits rays of light of a definite degree of refrangibility, and of a color peculiar to itself These rays are mingled with the rays that form the beam of light proceeding from the flame in which the element is ignited, and ordinarily are indistinguishable ; but if this beam be passed through a narrow slit, and directed upon a prism, the rays of different refrangibility and color are sepa- rated from each other, and those proceeding from the ignited element make their appearance in the form of narrow bright spaces or lines crossing the spectrum at right angles to its length. If, however, immediately behind the flame in which the element is ignited, another flame be placed much more intense than the first, and containing the same element in a state of more intense ignition, so that the rays of light which it emits will be'trans- mitted through the rays emitted by the element contained in the first flame, the rays of the same refrangibility in both flames will virtually destroy each other, just as the waves of different sounds sometimes do, producing perfect silence, so that when SPKCTKUM EXPLAINED. 273 the different rays are separated from each othor by the prism, certain rays will be found to be wanting, and dark spaces to have taken their places in which there is no light. If no\v, in the atmosphere of the sun the vapors of the various meta's be present in a state of intense ignition, their light passed through a prism and decomposed would produce a prism filled with bright lines, but if behind this external luminous atmosphere of th^ sun there be another source of heat still more intense, and containing these same metals in a state of mo;e intense ignition, and converted into luminous vapor, the first bright lines will be converted into dark lines by the absorption of the rays of light which produce them, and by the consequent for- mation of dark spaces in the solar spectrum in which there is no lijjrht. Now this is precisely the view which astronomers are disposed to give of the constitution of the sun. Within an external luminous Photosphere there is supposed to be an internal solid or liquid nucleus, in a more intense state of igni- tion. It is therefore highly probable that the unilluminated or dark spaces in the solar spectrum are produced by this cause, and that the vapors of the following metals Iron, Sodium, Po- tassium, Calcium, Magnesium, Manganese, Chromium, Nickel, Titanium, Hjdrogenium, Barium, Cobalt, and Aluminium, are contained in the sun's Photosphere, and most likely, also, Zinc, Copper, and Gold, and that these metals also exist to a considerable extent in UK; internal Nucleus of the sun. And that on the other hand, as the bright lines of the spectra of Silver, Mercury. Antimony, Arsenic, Tin, Lead, Cadmium, Strontium, and Lithium, also Silicon and Oxygen, do not coin- cide with any of the dark lines of the solar spectrum, therefore these elements do not exist at all in the constitution of the sun. 289.* The Solar Spectrum is sometimes crossed by bright instead of dark lines. If the light of the external Photosphere of the Sun could be observed by itself, alone, and separated from that of the internal nucleus, according to this theory, a solar spectrum would be obtained, crossed by the same system o\ Fraunhofer lines as now, only reversed, and made bright instead of dark. This state of things takes place during the occurrence of a total solar eclipse, for then the moon coming between the earth and the sun, completely cuts off all light proceeding from the bo'dy of the sun, and no light can reach the earth except that which proceeds from the solar Photosphere, and tlie incandes- cent vapors which surround it. AVhen the sun's disk is viewed 276 BRIGHT LINES. the strength and number of the dark lines by which their spec- tra are crossed. From this we infer that the constitution of the Fixed Stars is similar to that of the Sun, that is, that they till have an internal luminous nucleus, surrounded by an exter- nal luminous Photosphere less intensely heated. We are also able to ascertain with considerable accuracy the chemical con- stitution of these heavenly bodies. Thus Aldebaran contains Hydrogen, Sodium, Magnesium, Calcium, Iron, Tellurium, An- timony, Bismuth, and Mercury, while in Sirius, only Sodium, Magnesium, and Hydrogen, have been detected. 292.* Spectra of the Nebulae. The spectra of the Nebula, differ from those of the Sun and of the Stars, as they contain only bright lines, rnnng which the Nitrogen and Hydrogen lines are very apparent. Hence we conclude that the .Nebulas are only masses of glowing gas, and do not consist, like the Sun, of an incandescent solid or liquid nucleus, surrounded by a gaseous Photosphere. 293.* Spectra of Comets and Meteors. Observations upon the spectra of Comets seem to show that the nuclei consist of glowing gas, most probably containing Carbon, and that they not only emit their own light, but also reflect a portion of that of the Sun. On the other hand, the spectra of Meteors show that they are incandescent solid bodies, and that they differ from each other in chemical constitution, some containing Sodium, others Magnesium. 291*. Spectra of the Aurora Borealis and of Lightning-. T1 e spectra of the Aurora also exhibit very distinct and beautiful bright lines, but none that are coincident with those of any of the terrestrial elements. Hence we conclude that these are absent, or that the heat is not sufficiently great to make them luminous. The spectra of Lightning are also crossed by bright lines, some of which are coincident with those of Nitrogen and Oxygen, and are probably produced by the electrical ignition of the gaseous mixture of Oxygen, Nitrogen, Watery Vapor, and Carbonic Acid, through which the discharge is made. Thns we have the means, by carefully observing the light emitted by the various heavenly bodies, of -determining not only their physical constitution, but also the chemical elements which enter into them. This is the most brilliant generaliza- Describe the method of observing them. What is the principal substance discovered in the solar prominences ? 290*. Describe the spectra of the moon and of the planets 291*. Describe the spectra of the fixed stars. What elements are found in them? 292*. Describe the spectra of the Nebulae. 293*. Describe the spectra of Comets aud of Meteors. 294*. Describe the spectra of the Aurora Borealis, and of Lightning. THE EFFECT OF SOLAR LIGHT 277 tion of modern chemistry, and in this way does the chemist possess the power of extending his researches beyond the earth, and determining the chemical constitution of the sun and stars, and that too with a degree of exactness far surpassing that of the ordinary means of analysis. 290. The clfcct of Solar Light on the Vegetable Kingdom. The combined influence of the three kinds of rays contained in the sunbeam upon all objects exposed to their action is un- doubtedly very great. This is seen especially in the case of plants. Without the influence of the heating rays of the sun- beam, plants evince no signs of life, and in general, the higher the temperature, the more abundant and luxuriant the vegeta- tion. The effect of the illuminating rays is equally marked. In the dark, it is well known that the growth of plants is checked, and that their tissues are soon almost entirely deprived of their green color, and turn white ; their juices, also, lose their peculiar characteristic properties and become tasteless and Avatery. All plants tend to grow towards the light, and if placed in cellars, are soon bent in the direction of the windows. There is also a certain mechanical effect exerted by the solar beam ; under its influence the stomata of the leaves are opened, and the amount of air and watery vapor exhaled and inhaled is greatly increased ; if this influence be withdrawn, the stonata are at once closed, and the respiration of the plant is entirely suspended. Plants, therefore, placed in absolute dark- ness, speedily die. There is another effect, however, exerted by the chemical rays of the solar beam, of at least equal im- portance. The green parts of leaves and stems acquire the power, under the influence of sunlight, of decomposing carbonic acid, appropriating the carbon, and exhaling nearly pure oxygen. In the dark, this process is rever.-ed, and carbonic acid is ex- haled ; but as the amount of oxygen produced is much larger than the amount of carbonic acid, the general effect of plants is to diminish the amount of carbonic acid in the atmosphere, and to increase the amount of oxygen. They tend, therefore, to fit the air for the support of animal life, and to neutralize the injurious influences exerted upon the atmosphere by the car- bonic acid produced by the breathing of animals. There are two periols in the growth of plants when the amount of car- 29:). What is the effect of the heat rays of the solar beam on plants ? Of the illuminating rays ? What is the effect of light on the stomata of leaves? What happens if plants be pliced in complete darkness? What effect has light on the decomposition of carbonic aci'l by plants? Is this process ever reversed? At what two periods in the life of the plants is carbonic acid produced in excess? Vkat effect has light on oxidation? On de -oxidation? 278 ON VEGETATION, bonic acid evolved is greatly increased, viz., the germination of the seeds, and the bursting of the flower-buds; especially the former. This is owing to the fact, that in both these processes a large amount of carbon is removed from the starch contained in the seed and flower, in order that it may be converted into sugnr. Oxygen is, therefore, absorbed from the atmosphere to unite with this carbon and convert it into carbonic acid, which is then ex- haled. Both these processes are greatly assisted by the absence of light, and one of the indispensable conditions of vegetation is, that the seed be buried in the ground, and kept in the dark. The absence of light tends, therefore, to accelerate combination with oxygen, or to produce oxidation; the presence of light to set free oxygen from substances containing it, or to produce de-oxidation. It is by this latter process that all the carbon contained in plants has been abstracted from the atmosphere, by the agency of leaves, and also all the coal now found buried in the bowels of the earth. These influences are exerted chiefly by the chemical rays of the sunbeam, and they are greatly in- creased by covering plants with blue glass. This has the effect of absorbing the rays of heat and light, and leaving the plant to the exclusive influence of the chemical rays. 291. Summary of the effects of Light on Vegetation. The general effect of sunlight on plants may be thus summed up : 1st. The illuminating rays prevent the germination of seeds- 2d. The chemical rays, formed at the violet extremity of the spectrum, and extending a considerable distance beyond it, quicken germination. 3d. The luminous rays effect the decom- position of carbonic acid by the leaves. 4th. The chemical and luminous rays are both essential to the formation of the coloring matter of leaves. 5th. The chemical and illuminating rays, unassisted by the calorific rays, prevent the development of the reproductive organs of plants. 6th. The heat rays, cor- responding with the extreme red rays, assist the development of the reproductive organs of plants. There seems to be a nice adaptation of sunlight to the varying condition of vegetation, at the different seasons. In the spring, when the process of germination is going on, there is a large excess of chemical rays, which, as we have seen, tend powerfully to hasten the process. The excess of the chemical rays, at this season of the How has all the coal been abstracted from the atmosphere? By what rays of the solar beam has this been done? What effect has blue glass upon plants? 291. Give a sum- mary of the effect.-! of lig'it on vegetation. How does sunlight seem to be adapted to the var> int of hydrogen gas, arid introducing into the flame, which is almost invisible, a piece of platinum wire ; the light is at once greatly increased. Introduce fine iron, steel and copper wire ; a piece of glass tube ; the finely sharpened end of a piece of porcelain, 299. How do the ethereal vibrations which produce heat, compare in rapidity with those which produce light and chemical influence? Trace the gradual passage of the rays of he;it into those of light and chemical effect. May these forces be regarded as only different rates in the motion of the molecules of matter? . 12* 288 EXPERIMENTS. chalk and marble ; shake some calcined magnesia, and powdered charcoal, through the flaino ; in every case there is a great increase in the brilliancy of the light. The In drogen may be prepared by pouring sulphuric acid, diluted with five times its volume of water, and allowed to cool, upon granulated zinc in a glass flask, fitted with a cork, through which passes a glass tube, drawn out to a fine nozzle. The gas must be allowed to escape from the nozzle for at least five minutes before lighting, in order to completely expel the atmospheric air, otherwise there will be an explosion. 2. Galvanic electricity is a source of light ; this may be shown by binding a piece of well burned charcoal, or prepared carbon, to each of the wires attached to the poles of a battery of 12 Grove's cups, bringing the points near enough for the current to pass, and then drawing the charcoal points slowly apart to a short distance ; the light is very vivid. 3. Crystallization is a source of light ; this is best seen by dissolving transparent arsen- ious acid, or common arsenic, in boilii.g chlorohydric acid, until a saturated solution is made, and then allowing it to cool in a darkened room ; a flash of light may be seen to accompany the deposition of each crystal 4. Chemical action is a source of light ; this will become apparent from many of the experiments which are to follow, especially the burning of phosphorus in oxygen. 5. The law of the reflection of light may be shown in the same way as that of the re- flection of heat. See experiment 30, page 78. 6. The reflection of light may also be shown by the large parabolic mirrors ; see 75. p. 61. If one of these mirrors be placed opposite to the sun, a spot of extremely intense light and heat will be formed in its focus ; many of the metals will be made red-hot, and combustible substances inflamed. 7. The refraction of light ; this may be shown by a large double convex lens ; also by a solid prism of flint glass; or still more effectively by a hollow prism of glass filled with bi-sulphide of carbon. 8. The solar spectrum may be displayed to the best advantage by allowing a beam of sunlight to enter a darkened room through an exceedingly fine slit, in the manner de- scri>ed in 276. and receiving the spectrum upon a screen of white cotton cloth, placed at a distance of 20 feet from the prism. 9. The different heating power of the rays may be shown by placing a very delicate thermometer successively in the colored spaces, from the violet to the red, and finally a little below, and outside of the red ray. 10. The different illuminating power of the rays may be shown by holding a printed page successively in the different colors. 11. The different chemical power of the rays may be shown by placing slips of un- glazed white paper, that have been dipped in a colorless solution of nitrate of silver, and immediately afterwards in a solution of common salt, in the dark, successively, one slip in each color, from the red to the violet, and beyond the violet, for about one minute each ; or by exposing a piece of prepared paper to the action of the Avhole spectrum. See 278 and 279. 12. The power of sunlight to produce chemical combination, may be shown by mix- ing equal volumes of chlorine and hydrogen in a small glass tube, supported over mer- cury, in the dark, or diffuse dayl'ght, and reflecting a beam of sunlight upon it by a mirror ; only a small quantity of the gases should be employed. If a large quantity be used, the mixture should be placed in a bottle of white glass, in a wooden 'nox, with a movable cover, which may be drawn off by a string from a convenient distance. The ex- plosion is violent. The mode of preparing these gases may be seen by referring to the experiments under each. 1 3. The power of decomposing carbonic acid, imparted to green leaves by sunlight, may be shown by placing a thriving plant in a jar of carbonic acid gas, and exposing it to the sunlight for some days. Test the presence of the carbonic acid at the beginning of the experiment, by inserting a lighted taper; it will be extinguished. Prove the conversion of tie carbonic acid into oxygen at the close of the experiment, by introducing the same taper, re-lighted ; it will r.ow burn with increased brilliancy. 14-. That the leaves of plants emit oxygen in the sunlight, may be shown by placing a sprig of mint in a white glass globe, filled full of spring water, and then inverted in a tumbler of water, and placed in the sun ; in a short time babbles of gas will collect, which may be proved to be pure oxygen by their effect on a lighted taper. 1?. The effect of sunlight on cherried compounds, may be shown by pouring a little solution of common salt into a wine glass containing a solution of nitrate of silver, and exposing the white precipitate to the action of the sun ; it is almost immediately black- ened. 1 6. The different chemical effect of light of different colors, mar be shown by exposing slips of papor, prepared by dipping in a solution of nitrate of silver, and then in one cf common salt, in the dark, under pieces of blue, yellow and red glass, to the action of sunlight. The effect will be decidedly the greatest under the blue, and least under the red glass. ELECTRICITY. 289 17. Fraunhofer's lines may readily be seen by means of an instrument, arranged as in 283, or by the Spectroscope, 28ti, substituting sunlight, in place of artificial light. 18. The existence of chemical substances in tlames, may be shown by employing the Spectroscope, as described in 285 and 286, or by receiving the spectrum on a screen, as in 284. 19. The conversion of the bright lines of the spectra of artificial light into dark lines, may be shown by forming a spectrum upon a screen, by means of the Spectroscope, and the light of a powerful lamp, and noting the bright double sodium line in the orange ; this is due to the universal diffusion of sodium : then ignite a piece of sodium in a small platinum spoon, in a gas burner, placed so as to intercept the light of the original lamp in its passage into the Spectroscope, and the bright sodium lines of the spectrum will be at once converted into dark lines. The same experiment may be tried with equal effect with potassium and other metals. 20. The daguerreotype and photograph process may be illustrated by strictly following the directions contained in 293 and 294, with the aid of a good camera obscura, tak- ing care to protect the prepared plates carefully from the action of diffused light. The proportions of the solutions required are as follows : 1. Collodion, 5 or 6 grs. of gun cotton, to 1 oz. of mixture of 1 part of alcohol to 2 of ether, then add 2 grs. each of iodide of potassium, and iodide of cadmium. 2. Nitrate of Silver Solution, 480 grs. of crystallized nitrate of silver, to 2 oz. of water, with addition of 4 grs. of iodide of potassium, or cadmium. 3. Pvro-Gallic Acid Solution,! gr. of pyro-gallic acid, 30 minims of alcohol, 30 min- ims of glacial acetic acid, 2 grs. of citric acid, dissolved in 1 oz. of water. 4. The Hypo-Sulphite of Soda Solution should be saturated. If any difficulty be en- countered, further instruction should be sought from some experienced photographer. CHAPTER IV. THE THIRD CHEMICAL AGENT: ELECTRICITY. STATICAL ELECTRICITY J 'GALVANIC ELECTRICITY ; ELECTRO-MAGNET- ISM ; MAGNETO-ELECTRICITY; THERMO-ELECTRICITY; ANIMAL ELECTRICITY ; THE RELATIONS OF THE CHEMICAL AGENTS. I. Statical Electricity. 300. Electricity. The third of the three great imponder- able agents by which the action of chemical affinity is controlled, and which is either produced in all cases of chemical action, or has a powerful effect in producing them, is Electricity. There are two different states in which electricity is manifested, stati- cal and galvanic. The former is electricity in a state of repose ; the latter is electricity in movement. Statical electricity is principally produced by friction ; it accumulates upon the sur- faces of bodies, and exists in a state of tension, which is mani- fested by sparks, and by Ihe attraction which it exerts. Gal- 300. What is the third imponderable? In what two states does it exist? Describe them. 290 ITS NATURE. vanic electricity is principally produced by chemical action ; it ows for hours in a steady and continuous current ; and is particu- larly distinguished from statical electricity by its chemical effects, and its connection with magnetism. 301. The nature of Electricity* There are two hypotheses in regard to the nature of this powerful agent analogous to those which have been mentioned in regard to the nature of heat and light. The first regards it as an exceedingly subtile fluid, so light as not to affect the most delicate balances ; moving with immense velocity, and pervading all substances. The second regards it as the result of a special modification made in the state of bodies, depending upon a peculiar vibration of the par- ticles of matter communicated to the same ether, whose undula- tions produce heat and light. The latter theory is the one which is now generally received. The full discussion of all the phe- nomena of electricity would require a volume, and it properly forms a part of the sciences embraced in Natural Philosophy. We are concerned with it here only ?o far as it is connected with chemical phenomena, and as a knowledge of its fundamen- tal facts is necessary to the full understanding of the various chemical processes which are soon to come under our notice. The subject of galvanic electricity is of more importance to the chemist than that of statical, and our attention will, therefore, be chiefly directed to it. The fundamental facts on which the whole science of statical electricity is founded may be stated in a few words. 302. The fundamental facts of Statical Electricity. If a piece of glass, amber, or sealing-wax, be rubbed with the dry hand, dr with flannel, silk, or fur, and then held near small light bodies, such as straws, hairs, or threads, these bodies will fly toward the glass, amber, or wax, thus rubbed, and, for a moment, will adhere to them. The substances having this power of at- traction are called electrics, and the agency by which this power is exerted is called electricity. Some bodies, euch as certain crystals, exert the same power when heated, and others become electric by pressure. Although these are the simple facts on which the science is based, yet electricity exhibits a vast num- ber of curious and interesting phenomena, depending on the variety and kind of machinery, and the quantity of the elcctri- 301. State the two theories in regard to the nature of electricity. Which is now gen- erally received? 3^2. State the fundamental facts of electricity. What happens when gla^s, amher and sealing-wax are rubbed, and brought near small pieces of pnper ? When .is a body said to be excited with electricity ? What are the most common electrics ? TIIK SOURCES 291 cal influence employed. When a piece of glass, or other elec- tric, has been rubbed, so as to attract other bodies, it is said to be excited with electricity, or electrified, and it is found that many substances are capable of this excitement, when managed in a peculiar manner. The most common are amber, glass, rosin, sulphur, wax, and the fur of animals. 303. The sources of Electricity. The principal source of electricity for experimental purposes, is friction. Whenever two surfaces of any kind are rubbed together, one becomes ex- cited with negative, the other with positive, electricity. This, however, is only a special case of a much more general law, for it has been found that when the equilibrium of the molecules of any body is disturbed, a development of electricity takes place. The mere compression of many crystals is attended by electric action. A crystal of Iceland spar, if compressed, exhibits signs of electrical excitement, which it retains, sometimes, hours and days. The same is true of fluor spar, of mica, of arragonite, of quartz, and several other substances. Sometimes, elevation and depression of temperature are sufficient to develop electri- city. This is especially true of the mineral, tourmaline. If a crystal of this substance be gently heated, it becomes powerfully electrified while the temperature is rising, one extremity being positively, and the other negatively excited. When the tem- perature becomes stationary, the excitement ceases ; as the crys- tal cools, the electric excitement returns, but the polarity is reversed ; the end of the crystal that was before positive, now becomes negative. The temperature should not rise above 300. The electrical excitement of the. crystal may be shown by its power of attracting and repelling light substances brought near it. Fracture also produces electricity ; this may be shown by suddenly breaking a stick of roll sulphur. The rending of crystals along the line of clearage, as when the lamina? of a sheet of mica, or talc, are quickly separated in a dark room, is attended with a feeble electrical light. A melted substance, in the act of solidifying, is often electric. Melted sulphur, solidifying in a glass vessel, is negatively excited, wh.le the glass becomes positive. Ice is also often electric. This is probably due to molecular movements. Chemical action always produces electricity. Electricity is also developed in the pro- cess of combustion ; carbon, or- charcoal, when it burns, becomes 3^3. What is the principal source of electricity? To what is electrical excitement, in all c,u=es, thought to be due? What is the effect of compressing crystals? 01" hc:tii:^ aad cooling tourmalhio ? Of fracture? Of sblidLlcatiou of sulphur ? Of couibustiau J 292 OF ELECTRICITY. negatively electric, while the carbonic acid which it forms, is positive. In like manner, hydrogen, when it burns, is negative, while the watery vapor produced by it is positive. It is gaid, abo, that evaporation is a source of electricity, but this may be regarded as a case of chemical action. The evaporating sur- face is negative, while the vapor is positive. The atmosphere is also another source of electricity, not only during storms, but also in fine weather. Fogs, snow, and rain, are almost always charged with positive electricity. The clouds are also commonly highly positive. In general, all these sources of electricity may be resolved into the movement of the molecules of bodies, and their violent separation j all then become oppositely electrified. Thus electricity, like light and heat, may be considered as due to motion. 334:. Electrical Attraction and Repulsion. When an ex- cited electric, like a rod or tube of glass, which has been vio- lently rubbed with a piece of flannel, is presented to a small ball made of pith, or cork, and suspended by a silk thread, the pith ball is attracted to the glass, and adheres to it for a mo- ment, as in A, Fig. 114. Soon, however, it is repelled, and occupies the portion indi- Fig. 114. Electrical Attraction. cated by B. If now, to this pith ball, thus re- pelled, another pith ball be presented, this is first in like manner attracted, and then repelled, and so on with a succession of similar balls, which are each* in turn attracted, and repelled. From this experiment we draw the following conclusion, that if any electric be excited by friction, it will first at- tract, and then repel, a light substance placed near it, and that this light substance, when repelled, is itself in a state of dec- or evaporation ? What is the electrical state of the clouds ? What is the relation of electricity to motion? 304. What happens when an excited glass rod is brought m::tr a pith ball? When a second pith ball is presented to the first? What conclusion do wo draw from this experiment 2 TWO KINDS OF ELECTRICITY. 293 trical excitement, similar to the glass, proved by the fact that it first attracts, and then repels, another light body placed near it. A metallic rod being presented to the electrified pith ball, it will lose its excitement and return to i's natural condition. 305. Two bodies similarly electrified repel each other. If to a pith ball, thus excited, another pith ball, excited from the same piece of rubbed glass, be presented, they will mutually repel each other. And, in like manner, if a rod of sealing-wax, or sulphur, be violently rubbed with a piece of flannel, and then brought near to a pith ball, suspended by a thread, the pith ball will at first be attracted by the sealing-wax, and then repelled, and will be found to have become excited with electricity, simi- lar to that of the original sealing-wax : then, if to this pith ball thus excited, a second pith ball be presented, that has been excited by the same piece of rubbed sealing-wax, we shall find that these two pith balls, which have derived their electricity from the same source, will mutually repel each other. <.\ 306. Two bodies differently electrified attract each other. Two kinds cf electricity, Vitreous and Resinous. But if to a pith ball, excited by the rubbed glass, there be presented a pith ball that has been excited by a piece of rubbed sealing- wax, the two will mutually attract each other. Hence we con- clude that while bodies Fig. 115. The Electroscope. similarly electrified repel, bodies differently electrified attract one another. We also conclude that there is an apparent difference be- tween the electricity pro- duced by glass when rubbed, and the electricity produced by sealing-wax, and it is usual to speak of two kinds of electricity, vitreous and resinous, or positive and negative, and they are often denoted by the algebraic signs + an d 307. The Electroscope. On these properties is 315. What is the effect of two bodies similarly electrified upon each other ? 306. What eff ct have two bodies, differently electrified, \ipon each other? What is meaut by tb.a si^iis -{- and ? 307. Describe the electroscope. 294 CONDUCTORS AND NON-CONDUCTORS. X founded the instrument called the Electroscope, intended to indicate the presence of electricity in any body, and the kind of it. The two bits of gold leaf, n, n, in the accompanying Fig. 115, which are both connected with the brass head of the instru- ment, are similarly electrified when any excited electric is brought near to them, and repel each other more or le?s, ac- cording to the degree of this excitement. Let A be a rod of electrified sealing-wax, brought near to the knob, c ; the two bits of gold-leaf will be electrified, and will diverge from each other, indicating the existence of electrical excitement in A. The kind of electricity can be ascertained in the following manner. First, electrify the gold leaf with vitreous electricity, and then see, when the body whose electricity it is wished to determine, is brought near c, whether the slips continue to diverge, or come together ; if the former, the electricity is vitreous ; if the latter, it is resinous. The operation of this instrument will be more fully explained hereafter. o^fe^fc****'--:****. K 303. Conductors and Non-conductors. Insulation. If, in the preceding experiments, the pith balls be suspended from metal chains, having a direct metallic communication with the earth, none of the above phenomena Avill be manifested, for the electricity will pass off into the earth as soon as it reaches the balls, while the electrical excitement invariably makes i'self ap- parent if these be suspended from silk or glass. Hence we conclude that some substances conduct electricity very easily, and do not permit it to accumulate, while others deny it a pass- age. This is the foundation of the division of all bodies into conductors and non-conductors. A substance is said to be in- sulated when it is separated from all direct communication with good conductors of electricity by the intervention of a non-con- ductor, as when any body is placed upon a stool with glass legs, or a metallic rod is provided with a glass handle. No substance is capable of being permanent- Fig. 116. ] v electrified which is not a non-conductor itself, or made Metallic Rod with Glass Handle. b 7 insulation. Thus, ill Fig. 116, we have a bit of brass rod with a glass handle, and notwithstanding the conducting power of the metal, in consequence of its having a glass handle, it will, when rubbed, exhibit all the ordinary marks of electrical excitement. All substances exhibit electricity when rubbed, Show how the kirn! of electricity may be detected. 308. What is meant by conduct- ors and non-conductors 1 By insulation 1 THE INDUCTION 295 but those which are good conductors lose it immediately ; con- sequently, there are no signs of electrical excitement, except the escape be prevented by insulation. The metals, charcoal, plum- bago, water, and substances containing water in a liquid state, and therefore more or less damp, are conductors of electricity. Glass, resins, sulphur, diamond, dried wood, silk, hair, and woo!, also the air and gases, are non-conductors ; but these are often rendered conductors by the presence of water. For this reason, in damp weather, many electrical experiments can not be per- formed, because of the deposition of moisture upon the surface of insulators, and the good conducting power imparted to air by watery vapor. 309. Vitreous electricity can not be produced without a correspondent amount of resinous electricity, and vice versa. When two substances are rubbed together, both vitreous and resinous electricity are developed, the rubber being charged with one, and the substance rubbed, with the other; and the presence of both may be made manifest if the two substances in question are insulated. Thus, if a glass rod be rubbed with a pie;-e of flannel, while the glass will be charged with vitreous electricity, the flannel itself will be charged to an equal degree with resinous electricity. And on the other hand, if a rod of sealing-wax be rubbed with a piece of dry flannel, while the wax will be excited with resinous electricity, the piece of flan- nel will be charged to an equal degree with vitreous electricity. It is impossible to produce one kind of electricity without at the same time producing an equal amount of the opposite kind. This is the most marked peculiarity possessed by electricity, and this is the reason why it is called a polar force. By the term polar force, is meant a force which, whenever it is produced, always develops an equal amount of force over against, or oppo- site to itself, just as the poles of the earth are opposite to each other. The peculiar nature of a polar force is well illustrated in the case of a straight bar magnet, or a common magnetic needle, while one end is excited by one kind of magnetism, and points to the north, the other end is excited with the opposite kind of magnetism, and points towards the south ; and the? e two magnetic forces are mutually attractive of each other. In like manner, if one end of an insulated cylinder of brass be kept in a state of electrical excitement with one kind of electri- Mention some of the best conductors. Some of the best non conductors. What ia the effect of damp Aveather on electrical experiments? 309. Can vitreous electricity be produced without the manifestation of an equal amount of negative ? Why is electricity called a polar force? What is mean* by the term polar? Give an illustration of this. 296 OF ELECTRICITY. city, the other extremity will be excited with an equal amount of the opposite kind. This polar peculiarity of electricity will become more apparent as we proceed. 310. Induction of Electricity. One of the most curious facts connected with electricity is, the power that a highly elec- trified body has of throwing all other bodies near it into a sta'e of electrical excitement. Thus, an electrified glass globe, or other body, placed in the centre of a room, will produce elec- trical excitement in all objects in the apartment, and if they be insulated, sparks may be drawn from them. This is called the induction of electricity. When careful experiments are per- formed, it is found that if the body in question be charged with vitreous electricity, it will induce resinous electricity in the ex- tremities of those bodies which are nearest to it, while vitreous electricity will be manifested on those ends which are the most Let A be a rod of glass, positively elec- trified, and let it be brought near the me- tallic cylinder, B, in- sulated upon a stand of glass. B will im- mediately begin to give signs of electri- cal excitement, and it will be found, on examination, that the end of B nearest A will be negatively, while the most re- mote end will be positively electri- fied. If A be with- drawn, the signs of electrical excitement remote. This is illustrated by Fig. 117 Fig. 117. Induction of Electricity. in B will disappear. If it be again brought near, they will re- appear. Should a connection be formed between the remote end of B and the earth, the positive electricity will escape, and B will then contain only negative electricity, which will remain, after A is withdrawn. B is then left negatively electrified upon 310. What is meant by the induction of electricity? Is the electricity induced of the same kind as that of the excited body ? Explain Fig. 117. Is it possible to electrify a body without the actual contact of the excited substance? SOLID MATTER ^ 7 O OBSTACLE. 297 its insulated s'atid,' and if any body be now brought near to it, the negative electricity will escape with a spark. Thus an elec- trified body drives off electricity of the same kind, and puts bodies near it in an electrical condition opposite to itself. The polar relation of the positive or vitreous electricity, and the negative or resinous electricity, at the opposite extremities of the cylinder, B, is apparent ; and also the fact that one kind of electricity can not be developed without a corresponding devel- opment of the other. 311. The intervention of solid matter no obstacle to Induc- tion- This effect takes place even through glass and metallic ob- stacles placed in the way. Thus, in Fig. 117, if a plate of gla-s were held between the rod, A, and B, the effect would be the same. And so, in Fig. 118, if A be a metallic disk, insulated upon a glass Fig. 118. stand, B be a plate of glass, and c be an- other metallic disk, and if A b e electrified positively by an electrical machine, c will be immediately electrified also, through the glass, B, which will oppose no impediment to the process,and the right side will be charged with positive electricity, while thfj left side will be negative. If c be now touched on the right side with the finger, its positive electricity will escape, and it will remain negatively electrified, as represented in the figure. If, instead of using two disks, we paste a piece of tin foil on one side of a frame of glass, leaving a margin of an inch on every side, and on the other side a similar piece of tin foil, and electrify that on one side, the foil on the other side will be charged with the opposite electricity, if a connection be formed between it and the ground. Or, if a bottle be filled with cop- Solid Matter no obstacle to Induction. 311 Show that the intervent'on of a. solid body is no obsracle to induction. Describe Fig. 118. Show how induction operates i.i the case of the electroscope. 296 OF ELECTRICITY. city, the other extremity will be excited with an equal amount of the opposite kind. This polar peculiarity of electricity will become more apparent as we proceed. 310. Induction of Electricity. One of the most curious facts connected with electricity is, the power that a highly elec- trified body has of throwing all other bodies near it into a sta'e of electrical excitement. Thus, an electrified glass globe, or other body, placed in the centre of a room, will produce elec- trical excitement in all objects in the apartment, and if they be insulated, sparks may be drawn from them. This is called the induction of electricity. When careful experiments are per- formed, it is found that if the body in question be charged with vitreous electricity, it will induce resinous electricity in the ex- tremities of those bodies which are nearest to it, while vitreous electricity will be manifested on those ends which are the most remote. This is illustrated by Fig. 117. Let A be a rod of glass, positively elec- trifled, and let it be brought near the me- tallic cylinder, B, in- sulated upon a stand of glass. B will im- mediately begin to give signs of electri- cal excitement, and it will be found, on examination, that the end of B nearest A will be negatively, while the most re- mote end will be positively electri- fied. If A be with- drawn, the signs of electrical excitement in B will disappear. If it be again brought near, they will re- appear. Should a connection be formed between the remote end of B and the earth, the positive electricity will escape, and B will then contain only negative electricity, which will remain after A is withdrawn. B is then left negatively electrified upon Induction of Electricity. 310. What is meant by the induction of electricity ? Is the electricity Induced of the same kind as that of the excited body ? Explain Fig, 111. Is it possible to electrify a body without the actual contact of the excited substance? SOLID MATTER NO OBSTACLE. 297 its insulated s'ancVand if any body be now brought near to it, the negative electricity will escape with a spark. Thus an elec- trified body dri\ 7 es off electricity of the same kind, and puts bodies near it in an electrical condition opposite to itself. The polar relation of the positive or vitreous electricity, and the negative or resinous electricity, at the opposite extremities of the cylinder, B, is apparent ; and also the fact that one kind of electricity can not be developed without a corresponding devel- opment of the other. 311. The intervention of solid matter no obstacle to Induc- tion- This effect takes place even through glass and metallic ob- stacles placed in the way. Thus, in Fig. 117, if a plate of gla ; s were held between the rod, A, and B, the effect would be the same. And so, in Fig. 118, if A be a metallic disk, insulated upon a glass Fig. 118. stand, B be a plate of glass, and c be an- other metallic disk, and if A b e electrified positively by an electrical machine, c will be immediately electrified also, through the gla^s, B, which will oppose no impediment to Solid Matter no obstacle to Induction. ^he prOCCSS and the right side will be charged with positive electricity, while tho left side will be negative. If c be now touched on the right side with the finger, its positive electricity will escape, and it will remain negatively electrified, as represented in the figure. If, instead of using two disks, we paste a piece of tin foil on one side of a frame of glass, leaving a margin of an inch on every side, and on the other side a similar piece of tin foil, and electrify that on one side, the foil on the other side will be charged with the opposite electricity, if a connection be formed between it and the ground. Or, if a bottle be filled with cop- 311 Show that the intervent : on of a solid body is no obstacle to induction. Describe Fig. 118. Show ho.v induction operates i.t the case of the electroscope. 208 THEORY OF INDUCTION. per leaf, or have tin foil pasted on the inside, and the outside be covered with tin foil extending over the bottom, and three- fourths of the body of the bottle, and a connection be formed between the inside and an electrical machine, the outer side will also be electrified with the opposite electricity. This is the arrangement of the famous Leyden jar. In the case of the Electroscope, Fig. 115, the rod A, of sealing-wax being negatively electrified when brought near to c, induces in the knob positive electricity, as is seen in the figure, and negative electricity in the leaves of gold ; but both being similarly elec- trified, they repel each other in proportion to the degree of elec- trical excitement in A, until they touch the metallic slips, , , on each side connected with the earth. At the moment of con- tact, the negative electricity escapes, and there is nothing but positive electricity left in the knob, c, and the leaves. At first, these fall together, but almost immediately begin to repel each other under the influence of the positive electricity with which they are now both affected. 312. The theory of Induction. The difference between the conduction and induction of electricity consists in the mode in which the electrical influence is propagated from atom to atom, through bodies, so as to exert an effect at a considerable distance. If, when an electrified body is brought near to a body which is in its natural state, there be an instantaneous passage of the electri- city through the particles of the second body, the process is said to be conduction, and the body in question is called a good con- ductor. If, however, there is riot an instantaneous transmission of the electrical influence through the particles of the Fig. 119. second body$ but a certain amount of resistance of- fered to the passage of the electricity, the particles become polarized by induction ; and as each particle that is electrified induces electricity in those near it, Q Q Q# anc ^ throws them into a polar state, the effect may Q ttj ^ e P ro P a g ate d to a great distance. This is well a illustrated in Fig. 119. Let P represent any body charged with positive electricity, and abed rows of particles of air, intermediate between P and a second conductor, N. Air, as we know, is a poor conductor of electricity, and opposes some impediment to its passage; consequently, the particles of air between P and N, all become polarized ; i. e., their electrical 312. State the theory of induction. Show that it is accomplished by a process of polarization. Describe 'Fig. 119. CONFINED TO THE EXTERNAL SURFACE. 299 state is disturbed, and the negative electricity in each is drawn towards ihe positively charged body, p, while the positive elec- tricity in each particle is driven to the opposite pole and turned towards the conductor, N. The body, N, is also similarly affected, its negative electricity being strongly attracted towards the posi- tive electricity of the particles in d, immediately contiguous to it, and its positive electricity being repelled to the greatest pos- sible distance. This state of things will continue as long as p remains in its position ; but if that body be removed, the state of polar tension will cease, and the electricity of N, and the par- ticles of air will return to its natural state. 313- Electricity confined to the external surface of Bodies* This may be proved by the following experiment devised by Cou- lomb. A hollow sphere of brass, Fig. 120, is mounted upon a stand of glass, and pierced Fig- 120. with a circular aperture. It is highly "electrified by contact with an electrical machine, and its inner sur- face is touched by a stick of glass or gum lac, tipped with a small bit of brass, c. This piece of brass is then applied to the gold leaf electroscope, Fig. 115, and no divergence of the leaves can be observed. The bit of brass is next ap- plied to the outside surface of the globe, and then to the same electroscope, when a manifest divergence of the leaves is seen. Hence we conclude that there was no accumulation of electricity except upon the outside sur- face. This fact may bo proved by other experiments of a still more satisfactory charac- ter. It is found, al.-:o, that smoothness of the external surface has a great effect in retaining electricity and preventing it from escaping, while points and sharp edges greatly favor its escape. For this reason the prime conductors of electrical machines, and Electricity confined to the Surface. 3T.3. Show that electricity is confined to .the external surface of bodie*. What is tiio effect of the smoothness and roughness of surfaces on the escape of electricity ? 300 THEORIES OF ELECTRICITY. all the parts of Leyden jars, should be made as smooth as pos- sible. On the same principle, perfectly smooth surfaces, brought near to highly charged electrified bodies, receive electricity from them with great difficulty and always with a spark and shock, while edges and points will receive it from a distance, and silently, without either spark or noise. This is the principle on which lightning rods are constructed. They disarm the highly electrified clouds from a distance, noiselessly and quietly. These rods were first set up by Dr. Franklin, shortly after he made his great discovery of the identity of lightning and elec- tricity, by means of a kite raised in a thunder storm, in the neighborhood of Philadelphia. 314. Theories of Electricity. Two different theories have been proposed to account for the phenomena of electricity, that of. Dr. Franklin, and that of Dufay. To account for electrical phenomena, Dr. Franklin supposed, as above stated, that all terrestrial things had a natural quantity of that subtile fluid, but that its effects became apparent only when a substance contained more or less than the natural quantity, and that this state is pro- duced by the friction of an electric. Thus, when a piece of glass is rubbed by the hand, the equilibrium is destroyed, in consequence of the electrical miid passing from the hand to the glass, so that now the hand contains less, and the glass more, than their ordi- nary quantities. These two states he called positive and nega- tive, implying the presence and absence of the electrical fluid. If now a conductor of electricity, such as a piece of metal, be made to touch a positive body, or brought near it, the ac- cumulated fluid will leave this body and pass to the conductor, which will then contain more than its natural quantity of the fluid. But if the conductor be made to touch a negative body, then it will impart a share of its own natural quantity of the fluid to that body, and consequently will contain less than usual. Also, when one body, positively, and another nega- tively electrified, are connected by a conducting substance, the fluid rushes from the positive to the negative body, and the equilibrium is restored. This theory, originally invented ly Dr. Franklin, will account satisfactorily for nearly every elec- trical phenomenon. There is, however, another theory, that of Dufay, wh : ch is also very generally received. This theory sup- poses that there are two kinds of electricity, which are termed the vitreous and resinous, correspond'ng with the positive and Explain the principle of the lightning-rod. 314 What is the theory of Franklin ? Of Dufay ? Which is preferred ? THE ELECTRICAL 301 negative of Franklin. This supposition is founded on the fact, that when two pith balls, or other light bodies, near together, are bath touched by an excited piece of glass, or sealing-wax, they repel each other. But if one of the balls be touched by the glass, and the other by the wax, they will attract each other. Hence, Dufay concluded that electricity consists of two distinct fluids, which exist together in all bodies ; that these two fluids attract each other, but that they are separated during the excita- t'on of an electric, and that when thus separated, and transferred to non-electrics, as to the pith balls, the mutual attraction of the two electricities cause? the balls to rush towards each other. The electricity corresponding with the positive of Franklin, is called vitreous, because it is obtained from glass, while the other is called resinous, because it is obtained from wax: and resin. In respect to the merit of these two theories, we can only say here, that while Franklin's is the most' simple and accounts equally well for nearly all electrical phenomena, the preponder- ance of opinion is at the present time in favor of the theory of the polar character of electricity. It is regarded not as a fluid, but as a force, which acts at the same moment in opposite direc- tions. 315. Development of large quantities of Electricity .The Electrical XHachine- When large quantities of electricity are desired, it is obtained by means of the friction of a large sur- face of some non-conducting electric, such as g'ass ; this is accomplished by means of what are called Electrical Machines. There are two kinds, called the cylinder and plate machines, depending on the form of the glass used to excite the electricity. The plate machine is considered much the best, since bo:h sides are exposed to electrical friction, while in the cylinder machine only the outside can be excited. The plate machine is repre- sented in Fig. 121. It consists of a plate of glass, F, F, turning on an axis of wood, by the handle, M, and supported by a frame fixed to a platform, also of wood. On opposite sides are two cushions of leather, made to press against the plate by springs. From D, or some other part connected with the rubbers, a rod de- scends to the ground as a conductor of electricity to the machine. The electrical fluid accumulates on the surface of the prime conductors, c, C, which are insulated by glass supports in order to prevent the escape of the fluid. By means of such a ma- chine, especially if the cushions arc covered by soft mercurial 315. Describe the electrical machine. 302 MACHINE. Fig. 121. The Electrical Machine. amalgam, large quantities of electricity may be collected. On turning the plate, sparks are seen to pass from its surface to the prime conductors, being attracted by sharp points of brass wire, which issue from their smooth and brightly poll- lied sur- faces. A plate of two feet in diameter is sufficient for all ordi- nary purposes, but they are often made much larger, requiring the strength of several men to turn them. . 316. The Leyden Jar. An indispensable companion to the electrical machine is the Leyden Jar, so called from having been invented at Leyden, in Holland. It depends for its action 316. Describe the Leyden jar. THE LEYDEN JAR. 303 upon the principle of the induction of electricity, above ex- plained. It is necessary to bear in mind that glass is no impedi- ment to the induction of electricity by a highly charged electric, Tiie apparatus is delineated in the accompanying Fig. 122. It consists of a glass jar, coated both inside and out- side with tin foil, except a part around the top, as shown in the figure. The inside is sometimes also filled with gold or copper leaf. Through a var- nished wooden stopper, or through an ordinary cork, a wire having a knob at its top is passed, and extends to the inside coating. Now, if either posi- tive or negative electricity be communicated to the knob, it is immediately diffused over the whole of the inside coating, and by its inductive influence the outside coating takes on the opposite kind. When in this state, the two coatings being oppo- sitely electrified, the jar is said to be charged. The more the inside is charged, the more also, and io the eame degree, is the outside also charged. In this stale, as soon as a commun'cation is estub- Fig. 123. lislied between the in- side and the outside coatings, the two elec- tricities being mutually attracted, rush together with a bright flash and loud report, and the equilibrium is at once restored. The dis- charge may be effected through a short metallic circuit, as in the accom- panying Fig. 123, or through a long chain, cr through the fingers, or through a larger part of the body, the outside of the jar being grasped in one hand, and the knob touched with the fingers of the other hand ; or in fine, several peivons may form a circuit, by taking hold of hands, and the one at one extreme touching the outside coating, while the one at the other touches the knob. All will feel the shock Discharge of a Leyden Jar. How roav it be discharged? 13 304 THE THEORY OF THE LEYDEN JAE. at the same instant. It is usual to charge the jar from the elec-- trical machine, but it may also be charged from the Electro- phorus, an instrument to be presently described. 317. Mode of charging the Leyden Jar. While the jar is receiving the charge, it must not be insulated, i. e., the outside must communicate, through some good conductor, with the earth. As the positive fluid collects on the inside, the outside becomes negative, by the expulsion of the positive fluid natu- ral to it, and the accumulation of the negative fluid in its stead, drawn from the earth. But if the outside is insulated, these transfers to and from it can not take place, and therefore the jar can not become charged. 318. The theory of the Leyacn Jar. As the Leyden jar is charged by induction, the theory of the process is the same as that given for every process of induction, viz., that it is accom- plished by the polarization of the particles of an imperfect elec- trical conductor. Let No. 1, in Fig. 124, indicate a section of the glass side of a Ley- Fig. 124. ainst the plate, and in' a few minutes the electroscope will show signs of electric ex- citement. This is a delicate experiment. 7. That evaporation produces electricity, may be shown by placing a small tin dish upon the top of a gold leaf electroscope, having in it a red hot coal, just taken from the fire Sprinkle a few drops of water upon the coal and the evaporation will at, once canfe the gold leaves to diverge. This will not succeed either with charcoal or coke. It does best with a hot iron put into the water 8. To show that hydrogen, when it burns, products electricity, set fire to a jet of hy- drogen, so as to forip a flame about 3 inches in length ; then place a coil of platinum wire so as to be about 4 inches distant from the external surface of the flame, then let the upper extremity of the coil be bent so as to touch the plate of the electroscope, and signs of positive electricity will make their appearance. 9. To show electrical attraction and repulsion, perform the experiments described in 304 ; also, rub a glass rod with a piece of silk, and hold it near small pieces of paper, these bits will be first attracted, and then repelled. 10. To show that bodies similarly electrified repel, and differently electrified attract each other, electrify two pith balls by a piece of excited glass, and on bringing them near each other, repulsion will take place ; electrify one with a glass rod, and the other with a stick of sealing-wax, and bring them near each other, and attraction will ensue. These experiments may be multiplied indefinitely by means of the e'ectrical machine. 11. To show the induction of electricity, insulate a metallic conductor upon a glass stand, and suspend from one extremity two pith balls by distinct threads : then bring nenr to the opposite extrem ty an excited glass rod, as in F/. 117. and it will be found that the pith ball* will become excited with positive electricity, and repel one another ; remove the glass rod, and the pit.h balls will immediately return to their natural state ; bring it back again, and the electrical excitement will be restored. 12. If the insulated conductor be touched by the finger when excited by induction, a spark will be drawn from it, and the pith balls will collapse. By this process the posi- tive electricity will be withdrawn, and only negative electricity left upon the conductor, with which the pith balls will almost immediately become charged, and again repel each other. GALVANIC ELECTRICITY. 311 i V 1 3. Walk rapidly over a brussels carpet, on a cold day in vrinter ; this will charge the Carpet with electricity, and the effect will be to electrify, by induction, all the artic.es in the room ; apply the hand to the gas fixtures, aud a spark will be perceived ; this spark, if made to pass through the current of gis issuing from the burner, will be smncieiit to infl.ime it. All persons moving upon the carpet will become electrified, aui communi- cate sparks to those who enter tho room. These effects are not prevented by the inter- vention of glass screens between the excited electric and the conductor on which the electricity is induced. See Fig. 118. 1 4. An amalgam for the rubbers of the electrical machine may be made by melting i oz. of zinc in a ladle, and stirring into it 2 oz. of mercury ; when cold, pound it \vita a little wax or grease, and then spread it smoothly upon the leather with a hot spatula. 15. The electrical machine, for successful action, must have the plate thoroughly cleaned, be well dried and warmed, the rubbers provided with fresh amalgam, and t.ie prime conductor carefully cleaned from dust ; a metallic conductor should also lead from the rubbers to the ground. 1 6. The principle of the Leyden jar may be shown by pasting a piece of tin foil upon each side of a pane of glass to within an inch or more of the edge ; fasten a thread hold- ing a pith ball to the tin foil on each side, with a piece of wax ; connect one coating with the ground, and touch the prime conductor with the other ; the plate of glass will be- come charged, and the pich balls fly out to some distance ; then establish a connection between the two sides by a bent wire ; a shock wLl immediately pass, and the two balls will fall. 17. To show the mechanical effects of electricity, repeat the experiment indicated in Fig. 129. 1 8. To show the heating effect, pass an electrical charge through two wires nearly touching each other, in the bulb of a large air thermometer, Fig. 45 ; the liquid will immediately rise in the tube. 1 }. To show the physiological effect, pass the shock from a Leyden jar through a cir- cle formed by several persons joining hands ; the person at one extremity should gra.-p the outside of the bottle with moistened hands, and the one at the other should touch t'.ie knob with his moistened finger. The jar, in order to avoid the danger of falling, should be placed firmly upon a table. 20. The chemical effects may be shown by the apparatus indicated in Fig. 130 ; also, by pissing a spark through a jet of hydrogen issuing from a small tube ; or, through a jet of common illuminating gas; also, by passing a succession of sparks over a piece of paper moistened by a mixture of a solution of iodide of potassium and common starch ; the iodide is decomposed, i,/dine is set free, and a blue color struck by combination with the starch; also, by passing a succession of sparks through gold or platinum wires i.i- serted in a tube filled with water ; at each discharge bubbles of oxygen and hydrogen will rise from each wire ; when the tube is filled with gas so as to expose the wires, the next shock will cause the recombination of the gases with the formation of a small amount of water. 21. The magnetic effects may be shown by twisting a fine platinum wire into spiral, inserting a fine steel needle, wound with silk thread, in its axis, and passing a succession of electric shocks ; the needle will speedily become magnetic. For a more complete list of electrical experiments, the student is referred to a small work entitled " Electrical Experiments, by G. Francis." II. Galvanic Electricity. 322. Galvanic Electricity. This is the name given to that peculiar form of electricity which is produced by chemical ac- tion. It is generally called after its discoverer, Galvani, Gal- vanic Electricity, or Galvanism. As distinguished from Stati- cal Electricity, it is called Dynamical, because it is electricity 322. Ky whom was gilvanic electricity discovered 1 Why called voltaic ? What is the difference between galvanic and statical electricity ? 312 GALVANI'S THEORY. in action, prcrlucin^ force, and flowing like a current. It is al^o sometimes called Voltaic Electricity, from Volta, one of its most successful investigators. Galvanic electricity differs from stati- cal, in this respect, that the latter is more intense in its charac- ter and effects, producing more vivid sparks, and giving more violent shocks; while theformeris produced in a continuous and steady flow, and apparently in larger quantity. This difference will become more manifest as we proceed. 323. Discovery of Galvanism. The discovery of galvanic electricity was made by Galvani, the Professor of Anatomy in the University of Bologna, in the year 1790, and it was not known to exist until some time after the most important princi- ples of statical electricity, or the electricity of the machine, had been well established. The discovery is said to have been made in the following manner. It happened that several frogs lay upon the table of the laboratory, near to which Galvani's assistant was engaged in experimenting with an electrical ma- chine. While the machine was in action, the assistant acciden- tally touching one of the frogs with the knife which he held in his hand, the limbs of the frog became suddenly affected with convulsive movements. When the circumstance was re- ported to Galvani, he commenced a series of experiments for the purpose of discovering the cause of the strange phenome- non. With this view, he dissected several frogs, separating the legs, thighs, and lower part of the spinal column, from the remainder, so as to lay bare the lumbar nerves. He then passed copper hooks through the flesh above the legs, and suspended some of them by these hooks from the iron bar of the balcony of his window, in order to ascertain if they would be affected by the electricity of the atmosphere, and found that, whenever the wind, or any other accidental cause, brought the muscles of the leg into contact with the iron bar, the limbs were affected with convulsive movements, similar to those pro- duced by the sparks taken from the prime conductor of the ^X/ electrical machine. /\^ 324. Galvani's Theory. Galvani imagined that he had / ^fcere discovered the cause of muscular contraction in living ani- mals, and ascribed it to the influence of electricity. He sup- posed that this animal electricity originates in the brain, and is distributed by the nerves to every part of the system ; the different parts of each muscular fibril, he believed, were in oppo- I 323. In what manner did Galvani make the discovery ? 324. State his theory. VOLTA'S THEORY. 313 site states of electrical excitement, like the outer and inner sur- face of a charged Leyden jar, and that contractions of the mus- cle take place whenever the electricity is allowed to pass. This discharge, he supposed, was made during life, through the medi- um of the nerves, and in his experiments by means of the cop- per hooks and the iron. Thus, if, as represented in Fig. 131, the spinal cord of a frog were touched by a zinc rod, z, to the Fig. 131. GalvanVs Experiment. opposite extremity of which is attached a piece of copper c, and the copper wire then brought into contact with the outside of the frog's leg, the convulsive movements which take place he supposed were owing to the passage of the electricity from the nerve to the muscle, through the metallic conductors, exactly as a Leyden jar is discharged by a curved discharging rod, as shown in Fig. 123. These views were very generally adopted, and the new agent passed under the name of the galvanic fluid, . or animal electricity. 325. Correction of Galvani's theory by Volta. Volta, a Acelebrated Italian philosopher, and then professor at Como, ' afterwards at Pavia, already known by his invention of the 325. Give Volta's correction of Galvani's theory. 314 THE VOLTAIC PILE. electrophorus, the condensing electrometer, and the eudiometer, repeated the experiments of Galvani, and came to a precisely opposite conclusion. He found that the convulsive movements of the frog never took place when the metallic connector was formed of one single metal, but only when a compound con- nector was employed, composed of two metals, such as zinc and copper, as represented in Fig. 131. Hence he concluded that the electricity was produced by the contact of these two dissimi- lar metals, and that it was the nerve and the leg which consti- tuted the discharger ; precisely the reverse of the opinion of Galvani. After a long contest, Volta finally established his position, and showed that when two metals are made to touch each other, they become excited, the one with positive, the other with negative electricity, in all cases. Thus, when a piece of silver is placed upon the tongue, and a piece of zinc under it, and then their two edges are made to touch each other, there will be a passage of electricity from one to the other, which will be made sensible, not only by a peculiar metallic taste, but also by a slight flash of light before the eyes, especially if these Le closed. Again, on touching the knob of a delicate .condens- ing electroscope, containing two slips of gold leaf, as in Fig. 115, with a piece of polished zinc, the leaves diverge, and it can be shown that they are electrified negatively. This leads to the conclusion that by its contact with the zinc, the copper knob of the instrument becomes charged with positive electri- city, while the zinc is charged with negative. The quantity of electricity evolved by two pieces of metal being very small, Yolta tried the experiment of uniting many pieces in one series, and arranging them in pairs, with a conductor between them, and found that the electrical influence was increased in proportion to the number of plates thus combined. 32. The Voltaic Pile. These experiments finally led to the construction of the Voltaic Pile, the wonderful apparatus Avhich, under the name of the Galvanic Battery, has immortal- ized his name, and conferred lasting benefits upon man. The Voltaic Pile consists of several pairs of zinc and copper plates, placed one upon the other, with discs of thick fibrous paper, moistened with a solution of sulphate of soda, placed between each pair, and the pair immediately above it. Thus, first we have copper, then zinc, then paper ; after that, copper, zinc, paper, again. Give illustrations of the production of electricity by the contact of two metals. 326. Describe the yoltr.ic pile. How may siiocks be taken from this pile ? iiow may several piles l/e connected ? THE TRUE THEORY OF 315 It is quite evident that this order being strictly observed, while a zinc disc termi- nates the upper end of the pile, a copper disc will terminate the lower end. A wire being then attached to the extreme plate at each end, and the opposite ex- tremities being brought together, a flow of electricity takes place, which makes itself manifest by a faint spark when the wires are separated, and also when they are again united. The power of this pile in- creases with the number of pairs of plates employed. A pile composed of two doz- en plates of each metal will give a slight shock, which, when taken by the hands, may be felt up to the elbows. The mode of receiving the shock is to wet the hands, and then placing one of them in contact with the zinc plate which terminates one end of the pile, to touch with the other hand the copper plate which terminates the other end ; or, these two plates may be touched with wires wound with wet rags, and held one in each hand. When the galvanic current is to be passed through any substance, this is done by connecting a wire with each terminating plate ; the two wires are then brought near each other, and the substance being placed between them, the fluid passes from one wire to the other, and so through the substance in question. Any number of these piles may be connected together by making a metallic communi- cation between the last plate of the one, and the first plate of the other, always taking care to connect the copper end of each pile with the zinc end of the preceding pile. In this manner, a galvanic battery may be constructed, the power of which will be proportionate to the number of plates employed. 327. True theory of the Pile. Volta was of the opinion that the mere contact of the two dissimilar metals, zinc and cop- per, generated the electricity, and that the moistened discs only served as conductors to convey the electricity generated by one The Voltaic Pile. 327. What is the true theory of the pile? SI 6 THE PILE IS CHEMICAL ACTION. pair to the lower plate of the pair immediately next it ; and so on through the whole apparatus. It has since, however, been conclusively shown that the sole cause of the electrical current is the chemical decomposition of the saline solution by the zinc plates employed. In all cases of galvanic action, there must be a liquid composed of at least two chemical elements, susceptible of decomposition .by one of the metals, and not by the other ; the latter metal acting only the part of an electrical conductor. 338. Chemical constitution of the substances used to pro- duce Voltaic Electricity. Simple chemical action of one sim- ple substance upon another, such as bromine upon iron, is not sufficient to excite galvanic electricity. It must be such chemi- cal action as to produce the separation of the elements united in some compound substance. This separation can be effected by introducing some third simple substance, which has a stronger affinity for one of the elements in the compound than this has for the other. In all such cases the new element introduced goes to the formation of a new compound substance, by uniting with one of the original elements, and the other element, existing in the orig'nal compound, is set free. It is also essential that the compound to be decomposed should be in the liquid state, and the new element, introduced for the purpose of decomposing it, must be a solid. A second plate, consisting of a good conductor of electricity, must also be provided. The word, element, is here used in its strict chemical sense, as explained in 30. It would appear that as the molecular disturbance created by fric- tion is sufficient to produce the manifestation of statical electri- city, so the molecular disturbance produced by violently rending one chemical element from another, by means of the chemical affinity exerted by a third element, is sufficient to produce the manifestation of galvanic electricity. The compound liquid which is generally used in practice, is common wa.er, slightly acidulated with sulphuric acid, and the third element employed is metallic zinc ; for the conductor, the metals copper and pla- tinum are often employed, and sometimes common charcoal. Water is composed of the two elements, hydrogen and oxygen ; the oxygen is violently separated from the hydrogen by the zinc under the influence of affinity ; an oxide of zinc is formed on the one hand, and hydrogen is set free upon the other, and at the 828. Ts the simple chemical action of one substance upon another sufficient to produce galvanic electricity ? What sort of chemical action must it be ? In what state must the compound substance to be decomposed be? Is molecular disturbance really the cause of galvanic electricity ? What is the compound liquid generally used ? What is the de- composing metal employed ? PROOF THAT CHEMICAL ACTION" 317 same time a certain amount of electricity is evolved. In all tho.-e instances in which the simple contact only of different metals, without the employment of any liquid agent, has been found to produce electricity, it is always the case that the mois- ture of the air is really decomposed by the most oxidisable of the metals, while the electricity set free, is carried off by the 0:her. 329. Proof that Chemical Decomposition is the source of Galvanic Electricity. That chemical decomposition is the souive of the electricity of the voltaic pile is well shown by what is called a simple galvanic circuit. Let a glass cup be provided, Fig. 133, fill it about two-thirds with a mixture of 8 parts by volume of water to 1 of sulphuric ac^d ; then immerse in it a piece of brightly polished zinc, 6 inches in length, and as wide aS ^ 6 CU P W ^ a d m it- On immersing the zmc m tne acidulated water, bubbles of hy- drogen are at once abundantly discharged upon its surface, set free by the abstraction of' oxygen from the water by the zinc, and these bubbles rising through the liquid, at length escape into the air. Now place in the same vessel a slip of polished copper, and so No coiinfr.'iDit Leliueen -, ., , 1,1 i the Rates. long as it does not touch the zinc, no change will be observed, and the bubbles of hydro- gen will continue to escape as before, at the surface of the zinc plate. The instant, however, that any me- Fig. 134. tallic communication is made between the two plates, as in Fig. 134, where the two plates have been inclined so that the upper edge of the copper plate has been brought into contact with the zinc, it will be observed that the bubbles of hydrogen are no longer discharged upon the zinc, but upon the cop- per. There is no visible transfer through the liquid, but the faej is certain, and it is quite evident that an influence of some sort has been set in motion, by which the point of discharge for the gas has been trans- ferred to the copper, and a current produced, indicated in the 329. Prove that chemical decomposition is the source of galvanic electricity. Describe Fis- 133- -F'V- 134. What is the effwt of amalgamating the zinc plates? What other effects can be produced by the wires besides the evolution of gas ? 318 IS THE CAUSE OP THE CURRENT. figure by the direction of the arrow. Separate the two metals, and the gas ceases to be discharged upon the copper, and rises again from the zinc. If, instead of bringing the plates themselves into contact, the connection be made by wires, or any other good electrical conductor, the result will be the same ; Fig. 135. If the zinc, after being thoroughly Fig. 135. cleansed by immersion in the acidula- > \ ted water, be rubbed with mercury, it ^^) immediately acquires a bright amalga- mated surface, and when restored to the water, it no longer exerts any decompos- ing action, and particles of hydrogen are no longer seen to rise from it. The instant, however, that a connection is made by a wire, or otherwise, with the conducting plate, hydrogen bubbles at once begin to be discharged from it The Plates connected by a Wire. &S before. The Cause of this IS IK)t understood, but constant use is made of the fact to protect the zinc plates from corrosion, except dur- ing the period when the battery is actually in action. The evo- lution of gas is not the only effect observed ; the wires, if sepa- rated, will emit a spark of electricity. If they are wound around the bulb of a delicate air thermometer, (Fig. 45,) the liquid will rise in the tube, indicating the production of heat ; if they are wound about a piece of soft iron, the iron will become magnetic, and attract iron filings ; if one wire be applied to the crural nerve of a frog, and the other to the outside of the muscle, the leg will be violently convulsed; if dipped into acidulated water, it will be decomposed, oxygen will appear at one pole, and hy- drogen at the other. In short, the wires will emit sparks, pro- duce heat and magnetism, give shocks, effect chemical decompo- sition, and indicate the passage of a continuous current of gal- vanic electricity. 330. The decomposing 1 plate is the point of departure of the electrical current. -4t the same time that hydrogen is dis- charged upon the copper plate, a corresponding portion of ox'de of zinc is formed on the zinc plate by the affinity of the zinc for the oxygen of the water, and this oxide is eventually united with the sulphuric acid, converted into sulphate of zinc, and finally dissolved in the remaining water. If it were not for the 830. What is the point of departure of the electrical current? MODE OF TRANSFER 319 sulphuric acid, the oxide of zinc which is formed, being an in- soluble substance, would speedily cover the zinc plate with a thick deposit, and put a stop to its decomposing .action upon the water. By the introduction of the sulphuric acid, the oxide is removed as fast as formed, and converted into the soluble sul- phate of zinc, which is at once dissolved in the water. Thus .the zinc plate is kept bright, and its decomposing action is sus- tained until the water has dissolved all the sulphate of zinc of which it is capable. As soon as this point is reached, the oxide of zinc begins again to coat the zinc plate, and to diffuse itself in a cloudy precipitate through the water, thereby hindering the ready transference of the molecules of gas, and obstructing the pa^sacre of the electric current. By the combined opera- tion of both these causes, the process is brought to a conclusion. If some other chemical compound be employed, instead of water, which is capable of decomposition by the copper, and not by the zinc, the electrical current will be reversed, and will set out from the copper towards the zinc. In all cases, it is the metal which exerts the decomposing action by which the current is set in motion, and from which it starts, 331. Mode of transfer of the Hydrogen The mode in which the hydrogen is made to appear upon the copper plate is believed to be as follows. Oxygen is thought to be naturally charged with negative, and hydro- Fig- 13G. geu with positive, electricity ; con- sequently, as oppositely electrified bodies attract each other, when brought into close contact, these two substances unite under the influ- ence of this electrical attraction, and form water. Every particle of water consists, then, of two ele- ments, and a row of them extend- ing from the zinc to the copper plate, may be represented, as in Fig. 136. If now we suppose the i^Pp oxygen of the particle of water, next the zinc, to quit the hydrogen Mod* of Transfer of Hydrogen, with which it is united, and to connect itself with the zinc, as represented in the figure, and that a certain amount of electricity What is the use of the sulphuric acid? How is the process brought to a conclusion? 331 How is the hydrogen made to appear upon the copper plate? 320 OF THE HYDROGEN. 1 is excited by the transfer, which concentrates itself upon the deserted particle of hydrogen, then this particle of hydrogen, in consequence of the good conducting power of the copper, will be attracted towards it ; but corning into contact with the parti- cle of water next it, by its superior electrical excitement it ap- propriates its oxygen to itself, forming a new particle of water, and then communicates its electricity to the second particle of hydrogen thus set -free. This second particle of hydrogen is in turn started towards the copper plate, but in its way meeting with the next particle of water, it seizes upon its oxygen in the manner represented in the figure ; and so the process goes on, every particle of hydrogen set free, decomposing the particle of water next it in the shortest line of direction to the copper plate, until finally the last particle of water immediately touch- ing the copper plate is decomposed, and its hydrogen having nothing to unite with, is discharged, together with the accumu- lated electricity, upon the copper plate, and escapes. The elec- tricity thus produced finds its way back through the copper and the connecting wire, to the zinc, and thus returns to the point from which it set out. In this manner there is a continual pre- cipitation of particles of hydrogen upon the copper, and a steady current of electricity kept in motion, until the effect of the zinc upon the liquid ceases, and no more water is decomposed. In all cases, it will be seen that the current is from the zinc to the copper. There is good reason for doubting whether the theory described above, of the opposite electrical state of the oxygen and hydrogen is strictly true ; but there is no doubt of the trans- fer of the hydrogen, and that it is probably effected in the man- ner indicated. 332. The part played by the Copper. It is evident that it is the zinc which is the generating plate, and that the copper 'acts simply as an electrical conductor. Consequently, any good conductor of electricity will answer equally well, provided only, in all cases, it be not one which itself acts upon the acidulated water, because, in this case, an opposite current would be set in motion, which would neutralize the first. The conductor need not necessarily be metallic. Charcoal is employed in many of the best batteries, and in others, slips of platinum. In all case?, the conducting plate is charged with positive electricity, and the Describe the process of circulation which takes place. 332. What is the part played by the copper? Must the conducting plate be made of metal? What is the elcc rical condition of the two plates ? What is meant by a negative electric ? By a positive electric? THE POLARIZATION" 321 Positive and Negative Plates. generating plate with negative. In Fig. 137, the two pla es are distin- guished simply by the signs -j- and . The ends of the two wires, connected respectively with the two plates, are called positive and nega- tive poles, or sometimes positive and negative electrodes. Every chemi- cal element which appears at the positive pole is called a negative elec- tric, and every one appearing at the negative pole a positive electric. This is in accordance with the theory of electricity previously explained, that a body positively electrified will attract negative electrics, and a body negatively electrified positive electrics: 306. 333. The polarization and transfer of the elements of the Liquid, and the polarization of the Solid particles of the circuit necessary for the electrical force to circulate. The transference of the particles of hydrogen, arid the production of the electrical force, as just described, is supposed to be preceded by the polar- ization of the entire circuit, both solid and liquid. By po'ariza- tion is meant, as has been previously explained in describing the discharge of the Leyden jar, 316, the disturbance of the natural equilibrium of the electricity .residing in the molecules of a substance, and its distribution at the opposite poles of each molecule. Thus in Fig. 138, the upper row represents a series of particles of water, each corn- Fig. 138. Unpolarized Particles of Water. -Ao -Ao - Ao - posed of oxygen and hydrogen, in an unpolarized state; the second row represents the same particles of water in a polarized state, in which the particles have been turned around, and the negative oxygen made to alternate with the positive hy- drogen. This polar state is produced by bringing a highly charged positive electric into proximity with the negative oxygen, on the right of the figure. The oxygen is at once attracted, the hydrogen repelled and at the same time its positive electricity greatly intensified by in- H o AH o AH o A OAH oAw o> Polarized Particles of Water. 333 What is meant by the polarization of the liquid, as well as solid, part of the cir- cuit ? What is polarization? Describe Fig. 138. 322 OF THE ENTIRE CIRCUIT. Fig. 139. duction ; a similar change takes place in all the molecules, and the polariza ion is propagated throughout the series. Jn the case of the simple galvanic circuit, the polarization is supposed to be produced in the following manner : when the plate of zinc is introduced into the acidulated water, the part which touches the liquid, in consequence of the chemical action which takes place between it and the oxygen of the water, immediately becomes highly charged with positive electricity, while the opposite extremity, which is outside the cup, becomes negative ; this immediately polarizes the molecules of water, in the man- ner shown in Fig. 138. As soon as the copper plate is intro- duced, its molecules also become polarized, and the whole series extending to the extremity of the wire connected with that plate, is thrown into a similar state. The same process also takes place in the zinc plate, and is propagated to the extreme end of the wire connected with it, as shown in Fig. 139. As the ends of the wires, however, do not touch each other, there can be no discharge ; there is a state of polar tension produced, extend- ing through the circuit, but no discharge, and no current or mani- festation of electricity. Every thing, however, is ready for the discharge, and the instant the metallic connection is completed, it takes place. The first move- ment occurs on the right, at the lower part of the zinc plate. The first particle of oxygen is drawn off by the zinc, and its negative electricity seizes hold of the posi- tive electricity of the polarized particle of zinc next it, the negative electricity of this particle of zinc seizes upon the positive electricity of the polarized particle immediately adjoining, and thus the transfer of negative electricity proceeds from particle to particle up the whole length of the zinc plate, and through the wire connected with it. On the opposite side, at the foot of the copper plate, the reverse process is going on ; the hydrogen of the last particle of water is released from its oxygen and escapes into the air ; its positive Polarization, but no Discharge. State what takes place as soon as the zinc plute touches the acidulated water. Is there any discharge so long as the poles remain disconnected? Trace the process. PROOF OF ELECTRIC TENSION 323 electricity seizes hold of the negative electricity of the polarized particle of copper nearest it, and sets free its positive electricity ; this seizes upon the negative electricity of the next polarized particle ; the positive electricity thus set free seizes hold of the negative electricity of the particle next adjoining, and thus the transfer of positive electricity proceeds from particle to particle up the entire length of the copper plate, and through the wire connected with it. Consequently, there is a steady discharge of positive electricity from the wire connected with the copper plate, and of negative electricity from the wire connected with the zinc plate, and when the two wires are connected, these mutu- ally attract each other, remain united for a moment, and then separate, and pass on in opposite dire2tions. Thus, as Foon as the metallic connection is completed between the plates, the polar tension previously existing immediately springs into ac- tion, and a continued double circulation of electricity, in opposite directions, from molecule to molecule, is set up through the whole circuit, solid, as well as liquid; Fig. 140. In order to prevent confusion, however, when- ever the direction of the electrical current, is referred to, the direction of the positive current is alone mentioned. 334. Proof that a state of electrical tension exists in tho plates before the actual passage of the current. That this state of polar tension,, actually is pro- duced as soon as the zinc genera- ting plate and the copper or pla- tinum conducting plate are intro- duced into the acidulated water, may be shown by the following experiment, A plate of zinc,z, Fiy. 141, and another of platinum, P, are immersed in acidulated water, and the wire proceeding from each is insulated and connected with the two gilt disks, a and b, of the electroscope, E ; the^e disks are insulated by the glass of the apparatus ; they slide easily to and fro in sockets, and can be brought within a quarter of an inch of each other ; a sing!e gold leaf connected with the Polarization and Discharge, What takes place when the connection is made? Show that a doub'e current circu- lates. 334. Prove that a, state cf electrical tension exists before the passage of the current. 324 BEFORE THE PASSAGE OF THE CURRENT. Electric Tension before the passage of the Current. 14L plate of the instru- ment is suspended be- tween them. Now, if the positive end of a De Luc's dry pile, D, an instrument to be presently described, 349, be brought near the plate, this will become negative by induction, and the gold leaf positive, as indicated in the fig- ure. Under these cir- cumstances, however, if there were no electrical tension existing in either a or b, there would be no attraction of the gold leaf toward either, and it would continue unmoved ; but if there be an opposite state of electric tension in the two disks, it will be drawn towards that which is charged with negative, and repelled from that charged with positive electricity. On examination, it is found to be attracted towards the disk, a; and the conclusion, there- fore, is irresistible, that the zinc plate is in a state of negative electric tension. If now, the negative end of the De Luc's pile be presented to the plate of the instrument, this will become charged with positive electricity by induction, and the slip of gold leaf with negative electricity. In this state of things the gold leaf is attracted towards the disk, b, a conclusive proof that the plate, P, is in a state of positive electric tension, and this at a time when there is no direct connection between it and the plate, z. It is evident, therefore, that a state of electric tension is produced the instant the plates are introduced into the acidu- lated water, before the metallic circuit is completed. 335. The energy of the current proportionate to the chem- ical activity. If a metal be employed, in place of the zinc, which has a more powerful affinity for oxygen, and which will decompose water with greater energy and promptness, the inten- sity of the electrical current will be greatly increased. And as potassium the metallic basis of common potash, has a stronger affinity for oxygen than any other metal, this would form theo- retically, the best generating plate for a galvanic current ; there To what is the energy of the current proportioned ? What metal is the best gene- METALLIC CONNECTION" 325 arG, however, insuperable objections to its use, arising from the intensity of its action, its softness and want of durability, and its high cost. The experiment, however, admits of trial, by forming an amalgam of potassium with mercury, for it has been ascertained that the galvanic relations of all amalgams are those of the most oxidizable metal which they contain. On the other hand, the conducting plate must be composed of some metal exerting as little chemical action upon the water, and having as little affinity for oxygen, as possible. On this account, copper, and still more, platinum, are admirably fitted for this purpose. The reason for this necessity is, that in proportion to the affinity of the second, or the conducting plate for oxygen, does it tend to produce a counter current of electricity which neutralizes the primary current proceeding from the zinc, and proportion- ably reduces the energy of the circuit. Thus, in Fig. 1 40, if the copper pla f e had an affinity for oxygen equal to that of the zinc, it would tend to decompose the water, and set in motion a succession of particles of hydrogen, charged with positive elec- tricity, towards the zinc ; the result would be, that two opposing states of polar tension would be produced, and at the point of meeting, a particle of hydrogen on the one side, would be found arranged opposite to a particle of hydrogen on the other, and positive electricity against positive electricity, repelling each other with equal strength, and entirely preventing the passage of any current. In proportion as the conducting plate possesses an affinity for oxygen, does it tend to produce this result, and to stop the flow of the current. For this reason, it is necessary that the conducting plate should have the least possible affinity for oxygen, and be made of platinum, copper, gold or silveiv all of which have a feeble affinity for this substance ; and that the generating plate, on the other hand, should possess the greatest possible affinity for the same element, 335. The direction of the current is dependent upon the direction of the chemical action. In all these cases the positive electricity sets out from the more oxidizable metal which con- stitutes the generating plate, and traverses the liquid towards the less oxidizable metal which forms the conducting p!ate. The negative current, on the other hand, starts from the gene- rating plate, and turns its course in the opposite direction, i. e., parses up the plate, instead of through the liquid. Consequently, What, metal would, in theory, make the best generating plate? Why must the con- ducting plate be formed of some metal which exerts 110 decomposing action on water? 836. What is the direction of the current? 326 BETWEEN THE PLATES NOT NECESSARY. there is a current of positive electricity passing from the wire connected with the conducting, or copper plate, and of negative electricity passing from the generating, or zinc plate. 337- Direct metallic connection between the generating and conducting- plate not necessary. That direct metallic con- tact between the two plates is not necessary for the production of the current, may be shown by the apparatus represented in Fig. 142. Let z be a zinc plate, and r a platinum plate, hav- ing a platinum wire attached to it, and Fig. 142. k en t so as to touch a piece of paper, a, moistened with a solution of starch and iodide of potassium, and immersed in water, strongly acidulated ; in this case, it will be observed, there is no direct metal- lic connection between the two plates. Iodide of potassium is a substance com- posed of iodine and potassium ; the starch is a test for iod'rie, and is turned blue the instant any of the iodine is detached from, the potassium ; and as the electric current Contact not necessary. j m3 fa Q pQwer of detaching the iodine, if there be any electrical current transmitted from the platinum to the zinc plate, it will be at once manifested by the formation of a small blue spot at the point where the platinum wire touches the paper. Hence we conclude that the direct metallic connec- tion of the two plates is not necessary for the passage of the current, but that any good non-metallic conductor of electricity will answer equally well. This experiment also shows very satisfactorily that the contact of two dissimilar metals is not the cause of the galvanic current, and that the hypothesis suggested by Volta, in regard to the theory of the Voltaic pile is not strictly correct. 338. Effect of the discharge of hydrogen on the conducting plate. It will be observed in all the cases heretofore described, that as long as the circulation of the electrical current continues, there is a constant discharge of particles of hydrogen gas upon the conducting plate, whether it be made of platinum, or cop- per. The bubbles of hydrogen are discharged upon the sur- face of the plate at every point beneath the level of the water, and gradually stream upwards towards the air. In this way most of them escape, but a portion are detained by the strong 337, Show that direct metallic connection between the plates is unnecessary. 338. What is the effect of tiie dLseliarge of hydrogen ou the conducting plate? THE PLATINUM PLATE COATED WITH HYDROGEN. 327 Fin? Tan such a coated plate be used as the generating plate of a battery ? 339. Describe the gas battery. 14- 328 THE GAS BATTERY. been taken of this property to form what is called a gas battery ; Fig. 143. Two glass tubes, closed at one end, have suspended within them plates of platinum, each plate terminating in a cup filled with mercury, placed upon the summit of each tube. The tubes are first filled with acidulated water, and inverted into a glass vessel partially filled with the same mixture. The tube marked H, is then connected with the negative pole of a second galvanic battery, not shown in the figure, and the tube marked O, with the positive pole, by means of the cups filled with mer- cury, and the galvanic current passed through them, descending through o, and ascending through H ; as the current passes, the water in these two tubes is decomposed, and the hydrogen col- lects in the tube H, and the oxygen in the tube o, gradually expelling the acidulated water with which they are filled, into the lower vessel. The tube H is made of twice the capacity of the tube o, and the process is continued until both tubes are completely filled, H with hydrogen, and o with oxygen. The second battery is then entirely removed, and the two mercury cups connected by a wire, as shown in the figure. We have then a platinum plate in the tube H, surrounded by hydrogen, and dipping down into the acidulated water of the lower vessel, and a second platinum plate in the tube o, surrounded with oxygen, and dipping down into the acidulated water, and the plate in o connected with the plate in H, by a wire above. Under these circumstances, the hydrogen gas in H will act like a zinc plate similarly situated ; a state of polar tension is at once produced, running through the Avhole appa- ratus ; the lower end of H becomes positively electrified, as shown in the figure ; it seizes hold of the oxygen of the parti- cle of water nearest it ; its hydrogen appropriates the oxygen of the succeeding particle ; and so on, until the last particle of water is reached. The hydrogen of this particle is discharged into the oxygen of the tube, o, and at once resolved into water. At the same time, a current of positive electricity is set in mo- tion through the liquid, from H to o, then up the plate o to the wire, and finally is returned to the plate H, its course being indi- cated by the arrows. As particle after particle of hydrogen in the tube H, is united to the oxygen of successive particles of water, fresh portions of water .are formed in the tube H, which gradually fill it. At the same time, an equal number of parti- cles of water are formed in the tube o, by which it is also gradu- Explain how both tubes become gradually filled with water. BATTERY OF INTENSITY. 329 ally filled ; and when this takes place the process is brought to a conclusion. This very curious instrument establishes the important fact that hydrogen gas is capable, by its action on acidulated water, of generating a current of positive electricity. By connecting 8 or 10 such cells in succession, Fig. 144, in Gas Battery, Compound Circuit. such a way that the oxygen tube of one cell shall be connected with the hydrogen tube of the adjoining cell, very decided manifestations of the electrical current may be obtained ; bright sparks can be produced between charcoal points, and various chemical decompositions effected. 340. The Galvanic Battery. If the wire proceeding from the conducting plate, be it charcoal, or platinum, or copper, in- stead of being Fi S- 145- carried directly to the genera- ting zinc plate, be attached to the zinc plate of a second pair, in a second ves- sel, as is repre- _____ _=_ sented in Fig. . 145, the electri- Crown of Cups, Battery of Intensity. City generated 340 Inscribe the arrangement of the galvanic battery, name originally called. By whom invented. By what 330 BATTERY OF QUANTITY. by the first zinc will be communicated to the second, and being united to the electricity generated by it, will be transmitted through the fluid in the second vessel to the second conducing plate. The electrical current of the second pair is increased by the addition of the electricity of the first ; by the addition of a third pair, the power of the current is trebled ; and so we may proceed indefinitely, increasing the intensity of the electri- cal current by every additional pair ; but when we reach the end of the series, we must connect the conducting plate of the la t cup with the zinc, or generating plate, of the first cup, in order to make the circuit complete, and restore the electrical equilib- rium. Such an arrangement of connected cups and plates is ;< called a Galvanic Battery, from the powerful effects which it is capable of producing. It was first devised by Volta, after his invention of the Pile, and called by him the " couronne des lasses" or, crown of cups. As the entire merit of this cele- brated instrument belongs exclusively to Volta, and not at all to Galvani, it should be more properly called the Voltaic Bat- tery. 341. Batteries of Intensity and Batteries cf Quantity. It might be thought that an equal generating surface of zinc being employed in both cases, it would make no difference in the effect produced, whether we employed a great number of small plates, or a small number of large plates. It is found, however, in practice, that there is an important difference be- tween the effects of the two arrangements. The former will! yield electricity of great efficacy in effecting chemical decom- positions, the latter, electricity of great heat-producing power and magnetic Fig- 146. energy. A bat- tery that is adapted for the: former is called a Battery of In- tensity, and one that is adapted for the latter is called a Battery of Quantity. A battery of in ten - Battery of quantity. sity may be con- 341 What is a battery of in tensity? Of quantity? Describe the arrangement of each.. IMPROVED BATTERIES. 331 Ji- Fl verted into a battery of quantity, by breaking all the connections between the coppers and zincs of different cups, and uniting all the zincs together, then all the coppers, and at last establishing a connection between all the coppers and all the zincs by one single wire. In this way we practically convert all the zincs inio one large zinc, and all the coppers into one large copper plate; Fig. 146. 342. Improved Batteries. Instead of having the different pairs of plates in different cups, we may solder the zinc and copper plates together, and sink them into grooves in a trough, as in Fig. 147. In this case the plates themselves form the cups. The spa- Fig. 147. ces between the plates are filled with the exciting liquid to the same height. The electricity generated by the first zinc on the left is conveyed through the liquid to the opposite copper, and by it transferred to its companion zinc ; it is then transmitted through the next division of liquid to the succeeding copper, and so through the whole series, until it reaches the last cell at A. Into this, a conducting copper plate, a, is inserted and connected with the wire which carries back the electrical current to the beginning of the battery, where it is attached to another conducting plate, h, by which it is transferred to the first zinc plate. In Fig. 148, the same apparatus is seen in perspective. It is called Fig. 148. J Cruikdiank s Battery in Section. Cruikshantfs Battery. 342 Describe the arrangement of Cruikshank's battery. 332 SULPHATE OF COPPER BATTERY. Cruikshank's Battery, and is a very convenient form of the apparatus. 32.3. The Sulphate of Copper Battery. There is a second form of the galvanic battery in which the liquid to be decom- posed is not acidulated water, but water which holds in solution a quantity of sulphate of copper, sometimes called blue vitriol. Copper is employed for the conducting plate, and zinc for the generating pla'e. The sulphate of copper is composed of sul- phuric acid and the oxide of copper. Sulphuric acid is com- posed of sulphur and oxygen, and its composition may be rep- resented by SO 3 , i. e., one proportion of sulphur, and three of oxygen. Oxide of copper is composed of copper and oxygen, and its symbol is CuO, i. e., one proportion of copper, and one of oxygen. The symbol of the whole is CuO SO 3 . When the zinc plate is introduced into this solution it seems (o produce a double decomposition, and at the same time set on foot two processes of polarization and circulation ; Fig 149. In the first place, it produces a chain of polarized particles of water, and second, a chain of polarized particles of sulphate of oxide of copper, both extend'ng to the conducting plate ; then, the zinc draws off the oxygen from the water, and the hydrogen seizes upon the oxygen of the adjoining particle, as has been already described, until finally the last particle of hydrogen is projected upon the conducting plate. The oxide of zinc thus formed upon the zinc plate seizes upon the sulphuric acid of the sulphate of copper in contact with it,, setting free the oxide of copper, and forming sulphate of zinc, which is at once dissolved in the liquid. The oxide of copper, thus set free, seizes upon the sulphuric acid of the next particle of sulphate of copper ; and thus the process goes on, until finally a particle of the oxide of copper is pro- jected upon the conducting plate, at the very moment when the particle of hydrogen just spoken of, reaches the same point. (See the figure.) This hydrogen at once seizes upon the oxygen The Sulphate of -Copper Battery dissected. 343 Describe the sulphate of copper battery What 5s sulphate of copper? Give its svnibol. What double decomposition takes pl ace ? What becomes of the hydrogeu? Explain the deposition of the copper. What is the advantage of this battery. DANIELL S BATTERY 333 Tlie Sulphate of Copper Battery. 15 - of the oxide of copper, forming a par- ticle of water, and setting free metallic copper, which is immediately dis- charged upon the copper conducting plate. From this, it appears, that in this form of the battery the copper plate does not receive a deposit of particles of hydrogen, but, in its place, a deposit of copper. Consequently, there is no counteracting current of electricity, produced by hydrogen, tending to neutralize that which is produced by the generating plate, as has been shown to be the case in the simple galvanic circuit, and thus a great addition is made to the power of the battery. This form of the galvanic battery is of special use for the production of electro-magnetism, as will be shown hereafter. It is repre- sented in perspective in Fig. 150. 3-44. Danicll s Sulphate of Copper Battery. There is a practical difficulty in the operation of the sulphate of copper battery, that the zinc plate, is itself more or less covered by the particles of 'reduced copper, which act as so many secondary conducting plates, and tend to dissipate the force of the princi- pal current, and divert it into smaller channels. Another diffi- culty consists in the decomposition of the sulphate of zinc by the operation of the current, and the deposition of metallic zinc u;)on the copper plate, thus converting it practically into a zinc plate, and causing it to set up a counter current. These diffi- culties are overcome by separating the zinc plate from the cop- per plate by the intervention of a porous cup, and thus pre- venting the sulphate of copper from coming into direct contact with the zinc, and the sulphate of zinc with the copper. This j form of the instrument constitutes Darnell's battery, and the arrangement is as follows; Fig. 151. z represents a solid bar of zinc, placed in a cup of porous earthen ware, and filled with acidulated water ; c represents the copper plate, made in the form of a cylindrical cup, open at the top, and closed at the bottom, and filled with a solution of sulphate of copper. On the inner side of the rim of this cup is supported a copper shelf, pierced with holes, for the purpose of containing some crystals 344- What are some of the difficulties connected with the operation of the common battery? Describe Daniell's battery. Fig. 151. Danieirs Battery Dissected. DISSECTED. of sulphate of copper, which, by its gradual dissolving, may maintain the strenglh of the sulphate of copper so- lution placed below. As soon as the zinc and copper plates are connected by a wire, a steady current of elec- tricity begins to circulate, which will continue to flow for many hour?. The zinc, as soon as it is introduced into the acidulated water, decomposes it in the usual manner, and the libera- ted hydrogen is carried towards the conducting plate, directly through the porous cup. As soon as it enters the sulphate of the oxide of copper, it seizes upon the oxygen of the oxide, and is re-converted into water, giving up its electricity at the same moment to the copper of the oxide, which is at once de- posited upon the surface of the copper cylinder. The sulphuric acid which is set free from the sulphate of copper, represented in the figure by SO 3 , finds its way into the porous cup, where it assists in keeping up the strength of the acid solution, and is ulti- mately converted into sulphate of zinc by uniting with the oxide formed upon the surface of the zinc rod. The porous cup, though it is sufficiently firm to prevent the two liquids from mingling, opposes no impediment to the passage of the hydrogen through it in one direction, and of the sulphuric acid in the other, by the polarization of the chain of liquid particles which penetrates it. By this arrangement, the hydrogen is prevented from reaching the copper plate and setting up a counteracting current, arid the copper set free from the oxide, cannot pass through the porous cup and attach itself to the zinc plate. At the same time, the sulphate of zinc is prevented from passing over to the copper, depositing metallic zinc, and con- verting it practically into a second zinc plate, directly op- posed to the first. The result is, that such a battery will keep up a steady current of electricity for many hours, and hence is often called the constant battery. The actual form of this bat- tery is shown in Fig. 152. v represents a glass, or earthen- ware jar ; G, the copper cylinder, pierced with holes ; c, What becomes of the hydrogen? How is the copper plate prevented from being cor- ered with zinc ? GROVE S BATTERY. 335 Daniell's Battery. Fi g- 152 - the colander, filled with crystals of sulphate of copper ; p, the po- rous cup ; z, the rod of zinc ; p and n are thin strips of copper, for connecting with other cells. In this battery, the hydrogen is re- moved by chemical means. 35. Grove's Battery. In this battery, the hydrogen is also removed by chemical means, and it depends for its action upon the peculiar effect of this substance on nitric acid. This acid is a com pound of nitrogen and oxygen, and may be represented by the symbol l^O 5 , i. e., five proportions of oxy- gen, to one of nitrogen. Hydrogen discharged into this substance, decomposes it by appropriating one proportion of oxygen, forming water, and converting NO 5 into NO 4 , or, nitric into nitrous acid. The latter differs from the former, in po^e^sirig a deep red, or mahogany color, and emitting d; j ep red acid fumes. By this action, the hydrogen is transferred from the gaseous into the liquid state. In Grove's battery, the conducting plate is made of platinum, and is immersed in a po- rous cup, of clay, filled with strong nitric acid, and placed in the centre of a zinc cylinder, surrounded by acidulated water. In Fig. 153, z represents the zinc cylinder, open at both ends, and placed in a jar of glass or earthen-ware, filled with acidula- ted water ; p represents the platinum plate, placed in the interior of the porous cup, filled with strong nitric acid. The hydrogen, set free by the zinc, instead of being permitted to strike directly upon the platinum plate, passes through the porous cup into the nitric acid, where it is con- _^ verted into water by uniting with one proportion of the oxygen con- Battery, Dissected. tained in the acid, as represented in Fig. 153. 345. Describe Grove's battery. With what liquid is the porous cup fillet!? 14* 356 BUNS EN'S BATTERY. the figure, and converting it into nitrous acid; at the same moment, it yields up its electricity to the nitrous acid, by which it is conveyed to the conducting platinum. By this pro- cess, the nitric is rapidly changed into nitrous acid, a substance emitting a large quantity of red and acid fumes, and is also rapidly diluted by the drops of water steadily added to it. The strength of the nitric acid is therefore continually diminish- ing, and the constant action of this battery is not so great as Daniell's. By the complete and energetic absorption of the hy- drogen in this battery, power is amazingly increased, and it constitutes the best form of the instrument, being distinguished for the steadiness and intensity of its action; and 12 or 24 cups of it are quite sufficient for performing all the most brilliant galvanic experiments. In order to use several cups at once, tlie platinum plate of one pair must be connected with the zinc of the succeed- ing pair, and the termi- nating jolar wires at- tached, one of them to the extreme platinum, and the other to the ex- treme zinc plate. The actual form of the in- strument is seen in Fig. 154, where z represents the zinc cylinder, sur- rounded by acidulated water; v, the porous cup, filled with nitric Battery. acid, and containing the platinum plate, p ; b and , are screws, for the attachment of wires. This battery dis- charges a large amount of acid fumes, and it should always be placed in the open air, or in the strong draught of a chimney. 346. Eunsen's Battery. It is not necessary that the con- ducting plate be made of metal ; any good conductor of elec- tricity will answer equally well. Advantage is taken of this in Bunsen's battery, which resembles Grove's, exactly, except in the substitution of carbon cylinders for the platinum plates. What becomes of the hydrogen ? What is said of the intensity and constancy of this battery ? 346. Describe Bunsen's battery. SMEE'S BATTERY. 337 Fig- 155. Carbon is an excellent conductor of electricity, and on account of its great cheapness, compared with platinum, which is a very expensive metal, is much to be preferred. The form of the ap- paratus is much larger. The carbon cylinders are composed of solid gas coke, found in the inte- rior of illuminating-gas retorts, or else of powdered coke, mixed with sugar, and baked. Porous cups, of corresponding size, filled Bimsen's Battery. with nitric acid, are used. These batteries are sold in Paris for about 5 Francs the cup. Fig. 155. 347. Smee's Battery. This form of the battery is also designed to increase power by favoring the escape of the hydro- gen. It does so, however, by me- chanical means, instead of chemi- cal, and not so perfectly as in Grove's and Bunsen's batteries. It has been found that the bubbles of hydrogen adhere with considerable force to the smooth surfaces of conducting plates, but escape readily from the angles and edges. The conducting plate in Smee's battery is made of silver, roughened by the deposition upon it of spongy platinum from some solution in which it has been dissolved, and by this roughness of surface the discharge of the gas is much facilitated. Fly. 156. 348. Management of Batteries. In all these batteries, it is to be noted that the real source of the electric current is the decomposition of water by zinc; but this water must be acidulated with sulphuric acid in the proportion of 1 part, by measure, of acid, to 8 parts of water. When very energetic action is required, the solution may be made stronger. As great heat is produced on mingling the acid Battery. 317. Describe Smee's battery. 348. What precautions must be adopted iu the manage- ment of batteries ? 338 MANAGEMENT OF BATTERIES. and water, the mixture should be made some time before use, and allowed to cool. The nitric acid should be the strongest that can be procured, and never diluted. It is always decom- posed by the action of the battery, producing a ~large quantity of corrosive fumes, and should not be employed, therefore, in a closed room, or in one in which there is any nice apparatus. It is essential that the zincs be well amalgamated by dipping them info mercury, upon the surface of which floats a quantity of diluted chlorohydric acid, (muriatic acid.) The zinc is cleaned as it passes through the dilute acid, and the mercury immediately amalgamates with it, giving it a bright and smooth surface. They, should always be thoroughly washed in abun- dance of pure water, after use in the battery. The wires for connections should be of copper, well annealed, so as to be very flexible. The ends of these wires should be carefully bright- ened with a file, or by amalgamation with mercury before at- tachment to the binding cups ; in all cases, the ends of the bind- ing screws should be brightened by a file, pr sand paper, before use, and all metallic connections carefully examined. Not un- frcqiu'ntly the action of a very powerful battery is greatly impeded, or entirely stopped, by a slight film which has formed on some connecting surface. Where the electrical charge is to be passed through water for the purpose of decomposing it, the wa:er must ise acidulated. It is advantageous to have the coup- } ngs of the cells of a battery arranged in such a way that '.it can be used either as a battery of intensity, or a battery of quantity. The effects of these arrangements are widely dif- ierent, as will be seen hereafter. If it is desiredl^Tise a bat- tery of intensity, the conducting plate of the first cell should be connected with the generating plate of the second cell, and so on, in a regular series, as represented in Fig. 157. On the Fig. 157. Arrangement of a Battery of Intensity. other hand, if a battery of quantity be desired, the generating plates, i. e., the zincs, of all the cells, should be connected to- gether, and the conducting plates in the same manner, as rcpre- o f quantity ? DE LUC S PILE. 339 Fig. 158. T Arrangement of a Battery of Quantity. sented in Fig. 158. By such an arrangement, the various zinca practically become one large zinc plate, and the various con- ducting plates one large conducting plate, and the quality of the electricity produced is materially changed. 3 3:9. De Luc's Pile. Dry Pile. This is a galvanic arrange- ment, not requiring the use of any liquid,' and named from its inven f or. It was introduced shortly after the invention of the voltaic pile. It coasists of a number of alternation^, of very thin sheets of metal, with paper interposed between them. Thin paper, coated with gold or silver leaf on one side,, should b3 covered on the uncqated side with thin zinc foil. This paper should then b3 punched out into circular discs of about an inch in diameter, and these arranged in such a wa^ that the same order of succession, viz., zinc, paper, silver, zinc, paper, silver, should be preserved throughout, exactly as the discs are arranged in the voltaic pile. From 500 to 1000 such pairs are required to produce an active column, and they are most conveniently pi iced in a glass tube, perfectly clean and dry within, and sur- mounted at each end by a bra^s cap, perforated by a screw, which may serve to compress the discs, and also act as the poles of the pile, the screw at one end being in contact with the silvered side of the disc, and constituting the po-itive pole, and that at the other with the zinc disc*, and forming the negative pole. The electrical current in this pile is due to the slight oxidation of the zinc discs by the moisture contained in the paner. If the paper be artificially dried, the pile loses its ac- tivity, but again recovers its energy as the paper re-absorbs mo'sture from the air. Provided the two extremities of this pile remain unconnected, it will reta'n its activity for years ; but if the two poles are connected by a wire, the zinc discs become 319 Describe Pe Luc's dry pile To what is the electrical current in De Luc's pi'e due? What Ls the effect of drying the paper artificially? 340 GALVANIC AND STATICAL gradually oxidized, and the electrical power is destroyed. With a De Luc's pile containing 20,000 discs of zinc paper and sil- ver, sparks have been obtained, and a Ley den battery charged sufficiently to produce shocks. A more effective instrument is prepared by using finely powdered peroxide of manganese, in place of the gold or silver leaf. One surface of the paper disc is coated with zinc, the other with the peroxide, either dry or attached by honey and water. A metallic plate is placed at each end for a conductor and the whole series is tied together b|f silk thread ; the outside is then coated by dipping it in melted sulphur. The superior power of this instrument depends upon the affinity of the hydrogen, produced by the action of the zinc upon the moisture of the paper, for the oxygen of the peroxide, in virtue of which it is reconverted into water, and the paper kept continually moist. 330. Proof of the similarity of the electricity of the Hat- tsry and that cf the Electrical machine. The relation be- tween the electricity of the voltaic battery and that of the elec- trical machine, may be readily ascertained by means of a De Luc's pile. On applying such a pile, containing 500 or 1000 discs, by that extremity which is in contact with the last silver disc, and which, consequently, represents the end of the con- ducting plate in the common voltaic battery, to the knob of the gold leaf* electroscope, Fig. 115, whose leaves have been made to diverge with positive electricity, its leaves will still continue divergent. If the opposite, or zinc, end of the pile be then ap- plied to the electroscope, its divergent leaves will first coPapfe, and then diverge again. Consequently, we infer, (see #07, ]). 280,) that the silver end of the pile, or the conducting end of the common battery, is excited with positive, and the zinc erad with negative electricity. Thus a connection is established between the electricity of the conducting end of the battery, and that of the prime conductor of the electrical machine, and the electricity of the zinc end and that of the rubber of the Fame machine. If the wires attached to the two ends of a De Luc's pile be made to terminate in two small discs, which are brought within an inch and a half of each other, and carefully insulated, an insulated slip of gold leaf, suspended midway between the two discs, will first be attracted to the po-itSve disc, then repelled and attracted towards the negative disc, and thus a state of per- Explain the use of paper coated with the peroxide of manganese in place of the silver leaf ? 350. How may the similarity of the electricity of the battery, and that of the elec- trical machine, be proved by De Luc's pile? How may it be proved by the ordinary battery ? ELECTRICITY COMPARED. 341 petual oscillation produced which will continue uninterruptedly for months or years. The oppositely electrified state of the two poles of the voltaic pile may also be shown with the ordinary battery, by attaching the wire connected with one pole of a powerful battery to the foot of the electroscope, and the wire connected with the other pole to the knob or plate of the instru- ment, the gold leaves will diverge powerfully, the platinum end furnishing positive, and the zinc end negative, electricity. 351. The difference between Galvanic and Statical Elec- tricity- Galvanic electricity differs essentially from that of the electrical machine in possessing feeble intensity ; and therefore but little power of overcoming obstacles placed ii its path, giv- ing shocks and the like. It is incapable of producing many of the effects of the electrical machine, and its influence upon elec- trometers and electroscopes is extremely slight. A Leyden jar can only be charged with great difficulty by making a com- munication between one of its surfaces and one pole of the bat- tery, while the other surface is connected with the opposite pole. When the polar wires are brought near each other, only a feeble spark will pass, and on establishing the communication between them by means of the hands previously moistened, a shock is felt, but only for a moment. On the other hand, it is developed in much larger quantity than ordinary electricity, and in a steadily flowing current; it possesses, also, heating power of much greater intensity, extraordinary powers of chemical decom- po;ition, and a wonderful influence in producing magnetism. Moreover, if the current from a powerful battery be passed through the great centres of the nervous system, the most aston- ishing muscular contractions are excited. It is capable of pro- ducing, therefore, remarkable heating, chemical, magnetic, and physiological effects. 352. Galvanic Batteries of Historic Note. Among memo- rable apparatus of this class which have obtained celebrity in the history of physical science, may be mentioned the pile of 2000 pairs of plates, each having a surface of 32 square inches, at the Royal Institution, London, with which Sir H. Davy made his great discovery of the decomposition of the alkalies, potash and soda ; also the great pile of the Royal Society, of nearly the same magnitude. In 1808, the Emperor Napo- leon presented to the Polytechnic School, at Paris, a battery of 351. State the chief points of difference as to intensity, quantity, chemical decompose tion, magnetic influence, &c.. between the electricity of the machine, and that of tb, battery. 352. Mention some of the galvanic batteries of historic note. 342 HISTORIC BATTERIES. 600 pairs of plates, having each a square foot of surface. It was with this apparatus that several of the most important researches of Gay Lussac and Thenard, were conducted. Chil- dren's great battery, in London, consisted of 1 6 pairs of plates, each plate measuring 6 feet in length, and 2 feet in width, FO that the copper surface of each amounted to 32 square feet ; and when the whole was connected, there was an effective sur- face of 512 square feet. Dr. Hare's Deflagrator, in Philadel- phia, consisted of 80 pairs of plates, each zinc surface measur- ing 54 square inches, and each copper 80 square inches. Pej y's battery, at the London Institution, consisted of pairs of enor- mous size, composed of a sheet of copper, and a sheet of zinc, measuring each 50 feet in length, and 2 feet in width. These were wound round a rod of wood with horse hair between them. Each bucket conta : ned 55 gallons of the exciting liquid. With these batteries most extraordinary effects were produced. When the poles were dipped beneath the surface of water, a large quantity of oxygen and hydrogen was produced, and the water speedily grew very hot ; iron wire melted and fell down in globules, and steel burned with brilliant scintillation . Wiih Children's great battery many substances were fused which were exposed to the best wind furnaces without any effect. A p'ece of platinum wire, l-30th of an inch in diameter, and 18 inches long, became instantly red, then white hot, with a brilliancy in- supportable to the eye, and in a few seconds was fused into globules. When charcoal points were attached to the poles of the battery of the Royal Institution, a magnificent display of light was produced, the flame darting from one point to the oilier when they were four inches apart, and curving upwards in an arch. When any substance was held in this arch it became instantly ignited, platinum was melted in it, like wax in a can- dle, quartz, sapphire, magnesia, lime, all fused, arid the diamond and plumbago entered into combustion and disappeared in the air. These batteries, however, and all similar apparatus, power- ful as they were, and memorable as the discoveries in physics are to which they have been instrumental, have fallen into disuse since the invention of the batteries of Grove and Daniell, with two liquids. These, with a number of pairs of plate*, not ex- ceeding 40, and exposing a surface not exceeding 100 square inches each, produce a power equal to the largest of the batteries above described. Describe the effects produced by Children's battery, and that of the Koyal Institution. Why are fruese great batteries no longer used ? HEATING AND LUMINOUS 353. Heating- effects of the Galvanic Current. In all cases where electricity is in motion, the force is conveyed by the en- tire thickness of the conductor, and not by the surface alone. If the wire connecting the poles of a small galvanic battery be made to pass through, or be carried around, the bulb of an a r thermometer, as soon as the current circulates, a very perceptible effect will be produced upon the instrument. If the battery be large, and the wire small, the latter will become very hot, some- times be made red-hot, and actually melted. This is owing o the smallness of the diameter of the conducting wire, by which a large quantity of the electrical current is compelled to traverse a limited number of conducting particles in a given time. The rise of temperature in the wire is inversely proportional to its conducting power, and therefore the poorer the conductor, the greater the heat produced. This may be shown by forming a chain of alternate links of silver and platinum, and transmitting through it a current from a powerful battery. The silver being a good conductor of electricity, and not obstructing the passage of the current, exhibits no intense hea*, while the links of plati- num, in consequence of the poor conducting power of that metal, almost immediately become red-hot. The conducting power of the metals for electricity varies nearly in the same order as their power of conducting heat. Charcoal, however, though a bad conductor of heat, is an exceedingly good conductor of electri- city. Elevation of temperature diminishes the conducting power of the metals. This may be proved by transmitting through n platinum wire a galvanic current sufficient to make it red-hot ; and while the current is still passing, igniting a small part of the wire by the flame of a spirit lamp ; the rest of the wire immediately ceases to glow, in consequence of the obstruction at the point of ignition, and the Consequent diminution in the flow of the current. 354. Ignition produced. The heat produced by the elec- trical current may rise so high as to produce ignition of the most refractory substances. Carbon is the only substance which can not be melted by the pile, though with six hundred Bvmsen cells it has been softened to such a degree that adjoining pieces will adhere, which seems to indicate the commencement of fusion. 3 r )3. How may the heat of the connecting wire be shown by an air thermometer? What effect is produced upon the heat of the wire by reducing its size ''. To what is the rise of temperature in the wire inversely proportional? How may this bo shown by a ch;iin of alternate links of platinum and silver? What effect Iris Novation of tempera- ture on the cooductjug power of the mutais / 354. Describe cases of j^iiition produced by the current, 344 EFFECTS OF THE CURRENT. Platinum, which can not be melted by the most intense heat of a wind furnace, is immediately made white-hot, and fused by a powerful battery. It is said that if two platinum-poin'ed pen- cils, connected with the poles of the battery, be presented point to point, so that the current may pass between them, they will be fused and soldered together, and that this effect will be equally produced under wa'er. The other metals are not only melted, but volatilized, and dissipated in vapor. Iron and pla- tinum burn with a shining white light; lead, with purple; tin and gold, with bluish light ; zinc, with white and red ; copper and silver, with a greeni-h light. These effects are displayed with increased splendor if the metal to be burned be attached to a wire connected with the positive pole, and then applied to the surface of mercury connected with the negative pole. If a piece of steel watch spring, thus attached, be brought near the surface of a cup of mercury connected with the negative pole, the most beautiful scintillations will be produced ; a steel file will answer nearly the same purpose. If two steel or iron wires, connected with the two poles, be brought near each other, vivid sparks will pass from one to the other, and if they both be coated with lamp-black, by holding them in the flame of an oil lamp, the sparks will be much brighter, especially if the two wires be held opposite each other, directly in the flame of the lamp. 355. Luminous effects. All combustible substances, whether solid or liquid, such as ether, alcohol, phosphorus, and gunpow- der, may be inflamed by passing the galvanic current through them. A platinum wire, several yards in length, can be made to glow With intense brilliancy; and the effect is greatly in- creased if the wire be wound into the form of a spiral helix. Oxygen and hydrogen gases ; also, hydrogen and chlorine, are combined by the spark, with a bright flash, and loud explosion. When pieces of well burned charcoal are attached to the wires, and become the poles of the battery, on bringing them near each other, a most brilliant arc of flame, emitting the brightest artificial light known, flashes between them. The compact coke of gas retorts is better adapted to this purpose than any other form of charcoal. The points must be brought near each other, and then gradually separated, Fig. 159 ; a is the positive pole, b the negative. As they are drawn apart by the rack and How may the splendor of the light produced by the burning metals be increased ? 355. Describe the luminous effects produced by charcoal points. What arrangement of the points increases the luminous effect ? DUBOSCQ'S ELECTRIC LIGIIT. 345 Fig- 159. pirron, the light and flame still continue, assum- ing the form of a curved arc. If the different met- als are placed in this flame they are volatilized at once, and pass off in fumes. So intense is the light, that it may- be used in opti- cal experiments in place of the light of the sun. The luminous ef- fect is found to be increased if the upper piece of carbon be made the posi- tive, and the lower the negative pole. And if the two carbon points are arranged in a horizontal position, at right angles to the magnetic meridian, the length of the luminous arc is said to be greater in the proportion of 20.8 to 16.5, when the positive pole is to the east, than when it is to the west. 356. Duboscq's Electric lamp. During the production of this dazzling light there is a considerable transport of the particles of carbon from the positive to the negative pole. A cavity is always produced in the carbon connected with the posi- tive pole, and a deposit, continually increasing in length, is formed upon the negative pole. In Fig. 160 is represented an exceedingly ingenious apparatus for keeping this light at a fixed point in space so that it may be used in the solar microscope. Ordinarily the position of the light is continually changing as the negative pole is increasing at the expense of the positive ; and this unfits it for use in connection with lenses ; but in this apparatus this difficulty is overcome, and when placed in the 356 "What change takes place in the length of the charcoal points during the passage of the current? If the position of the light be made fixed, for what purpose may it be used? Describe Fig- 160. Luminous Effects of the Battery. Charcoal Points. 346 NOT PRODUCED BY COMBUSTION. Fig. 160. Duboscq^s Electric Lamp. microscope, the image of the two points is formed upon a screen at some distance, upon an enlarged scale. From this image, as shown in the figure, the peculiar shape assumed by the two poles can he plainly seen, and also the process of trans- port, by which one increases at the expense of the other. This exceedingly elegant instrument is the invention of M. Duboscq, of Paris, and is intended to be used in the performance of opti- cal experiments, in place of solar light. 357. Discovery of the Electric Light Sir H. Davy, in 1801, at London, was the first to perform the experiment cf the electric light, and with the great battery of the Royal In- stitution, consisting of 2000 pairs of plates, obtained an arc of flame between two charcoal points, 4 inches in length. This charcoal had been prepared by heating it red-hot, and then quenching it beneath the surface of mercury. Despretz, how- ever, with 600 cells of Bunsen, arranged consecutively, suc- ceeded, when the points were placed vertically, the positive pole being above, in obtaining an arc 7.8 inches in length. 358- The Electric Light is not produced by Combustion. That this is not a case of ordinary combustion of charcoal in air, simply increased by the action of the galvanic current, may 357. Who was the discoverer of the elertric light ? What results did he a ttain ? length of arc was obtai.-.ed by Despreta ? 358. Show that the electric light is i duced by coinbustiou Wh:.t not pro. INTENSITY OF THE ELECTKIC LIGHT. q 7 0-17 Fig. 161. be shown by placing the charcoal points in the interior of a glass vessel, from which the air has been withdrawn by the air pump, Fig. 161. It will be found that the light is quite a-; great as before. It can even be produced beneath the surface of water, but is consider- ably diminished in splendor. The light is in great part due to the continued transport of minute particles of carbon in a state of in- tense incandescence. 359. The properties and intensity of ths Electric Light. The heat produced in the voltaic arc is of the most intense kind. Pla- tinum, iridium, and titanium, which resist the greatest heat of the most powerful wind fu - nace, readily melt, when placed in it. The light is powerful enough to produce the com- bination of chlorine and hydrogen at a con- siderable distance, and without any direct con- tact, and to act upon the chloride of silver, i:i the same way as the light of the Fun. It also po-sesses the singular property of being at- tracted by the magnet. Transmitted through a prism, the electric light is decomposed, and produces a spectrum like that of the sun, with lines analogous to the lines of Fraunhofer, ex- cept that they are bright, instead of dark. The character of these lines depends upon the metal with which the poles are tipped. The light produced by 18 cells of Bunsen, has been estimated as more than that proceeding from 572 candle*; under the mo t favorable circum- stances, it has been computed as equal to one-third of the inten- sity of solar light, and is so bright that it can not safely be re- girded by the naked eye. 363. Connection between the heat of the Battery and the mechanical equivalent of Heat. The chemical action within the battery always produces heat, and a definite amount of chemical action a definite amount of heat ; no more and no less. It has been ascertained, however, that if heat is developed at any point in the circuit outside the battery, the amount cf heat produced within the battery is diminished in an equal ratio, 359 What degree of heat ia produced by the voltaic arc? Of light? If the light l>e transmitted through a glass prism, what may be observed? How docs it compart! v.-itli the light of the sun ? 3'iO. If a portion of fie power of fie battery be used to produce motion, wiiat uil'ect is produced, upon, tke lieat of tiie battery 1 Charcoal Points in Vac no. 348 THE CHEMICAL EFFECTS OF THE CURRENT. and that if the electrical current be used to produce motion, as it may be, when employed to generate electro-magnetism, a por- tion of the heat of the entire circuit disappears, having been con- verted into mechanical effect or motion. The quantity of heat which disappears corresponds very nearly to that which Joule's law, ( 254,) would require for the production of an equal mechan- ical effect. This serves to confirm, very strongly, the mechanical theory of heat. 361. Heating- effects are best produced by batteries of quantity. In experiments on the heating effects of the galvanic current, the battery should be arranged ?o that the zinc plates may all be connected together, practically forming but one zinc plate, and the platinum plates, in the same manner, forming but one platinum plate, as shown in Fig. 158. 362. The chemical effects of the galvanic current. Its de- composing 1 power. The chemical effects of the voltaic current are even more remarkable and interesting than the heating. It had been noticed in Holland, in 1798, that a succession of charges of statical electricity transmitted for a long time through water, by means of platinum or gold conductors which' nearly touched each other, effected the decomposition of water; and in 1800, shortly after the invention of the voltaic pile, it was discovered by Nicholson and Carlisle, two English chemists, that a current of galvanic electricity would not only decompose water, but that the oxygen would invariably be discharged at the positive pole, and the hydrogen at the negative. This ex- periment led to the application of the galvanic current to other chemical compounds, with a view to effect their decomposition, and enabled Sir H. Davy, a few years afterwards, to decompose the alkalies, potash and soda, which heretofore had been re- garded as simple substances, and to prove that they were com- posed of oxygen, and two different metals, potassium and sodium. This great discovery was the prelude to others of a similar kind, and led to the establishment of an entirely new theory in regard to the constitution of the various rocks, minerals, earths, and salts, of which the earth is composed, viz., that they all possess a metallic basis, and have been produced by the combination of different metals with other simple substances, chiefly gaseous. , 363. The constitution of Water. Pure water is a compound Is there any correspondence between the amount of heat thus conTerted into motion, and that which is required by Joule's law? 3G1. Which kind of battery produces the greatest heating effect .' 332. Who discovered the chemical effect of the current ? Wh:;t use did Sir II. Davy make of it ? 333. Describe the composition of water by volume, and by weight, as shown by its decomposition THE DECOMPOSITION OF WATER 349 of two gaseous chemical elements, oxygen and hydrogen, and hence is called a binary compound. It is al o composed of these substances, united in certain definite proportions, both by weight and by volume. By weight, the proportion of oxygen to hy- drogen is 8 to 1 ; by volume, it is as 1 to 2. Hence, if we wish to produce water by the cornbinatio i of these two substances, we must use 8 parts by weight of oxygen, to 1 part by weight of hydrogen ; but by volume, 1 measure of oxygen, to 2 meas- ures of hydrogen ; and these 8 parts by weight of oxygen, com- bined with 1 part by weight of hydrogen, make exactly 9 parts by weight of pure water. On the other hand, if we decompose pure water, we always obtain one volume of oxygen, to two volumes of hydrogen, and every 9 grains of water decomposed produce just 8 grains of oxygen, and 1 grain of hydrogen. From this, it appears that the proportions in which elements un'te, by weight, to form compounds, are very different from the proportions in which they unite by volume. When one volume of oxygen, and two volumes of hydrogen, or which is the same th'ng, eight parts by weight of oxygen, and one part by weight of hydrogen, are introduced into a closed receiver, and a spark from the electrical machine is passed through them, an explosion re ults, the gases disappear, and watery vapor is formed, which, on the cooling of the vessel, condenses into little drops of water. The, weight of the water formed is always precisely equal to the sum of the weights of the two gases employed. 364. The decomposition of Water by the Battery. If two platinum or gold wires be attached to the poles of the battery, and then be brought near each other beneath the surface of water slightly acidulated with sulphuric acid, bubbles of oxygen gas will appear at the positive, and of hydrogen at the negative pole. If tubes, closed at the upper end, ana open at the lower, be completely filled with water, so as to retain no bubbles of air whatever, and then inverted over each pole, the bubbles of each ga> as they arise, will be collected separately in the two tubes, tli"} oxygen in the tube over the positive pole, and the hydrogen in that over the negative pole, and twice as much of the latter as of the former; Fig. 162. As the hydrogen is collected in double the quantity of the oxygen, the tube containing it should- be made twice as large as that for oxygen ; the process may be continued till both are filled ; and this will take place at the same instant. Can w?ter be reproduced by uniting these elements iu tae same proportions 1 854. Desc.ibe the decomposition of water by ti.e curreut. 350 EFFECTED BY THE POLARIZATION Fig. 162. Decomposition of Water. On carefully closing the oxygen tube beneath the water, and invert- ing it, so that a lighted taper can be introduced into it from above, the taper will be found to burn with extraordi- nary splendor, and if blown out in such a way as to leave a small smou'dering spark upon the wick, it will be re- lighted when it is intro- duced again into the gas. On the other hand, if the hydrogen tube be lemoved with equal care, but not inverted, and a lighted taper introduced into it from, below, the hydrogen will take fire, and bum with a lam- bent flame, but the taper will be extinguished. Thus, the: e two ga^es may be distinguished by their opposite effects upon a lighted taper. If, instead of using two tube?, one tube be nTed with water, and inverted over both poles, the two gases will be colected together, and if a spark from the electrical machine be passed through the mixture, there will be a flash of 1'ght, and an explosion ; the two gases will unite to Ibrm a very small por- tion of water, and will entirely disappear, and the water from the vessel will rush up so as to completely fill the wl.ole of the tube. In performing this experiment, it is necessary to use a platinum wire for the positive pole at which the oxygen is dis- charged, for if a copper wire be employed, or any other metal which has a strong affinity for oxygen , the gas will unite with the metal to form a solid oxide, instead of escaping and ris'ng through the liquid. Platinum and gold have only a very slight affinity for oxygen, and, therefore, when these are used, nearly the whole of the gas is collected. It is advantageous in all such experiments to have bolh wires made of p^tinum. From this experiment, it is evident that the galvanic current has the power of decomposing water, and separating it into its constituent ele- ments. 365. The decomposition of Water is effected by the polari- zation and transfer of the component elements- It has been Which gas collects in the larger quantity? How may they be tested, and proved to be different ? Y~ny must tue decomposing wires be made of platinum t AND TRANSFER OF THE ELEMENTS. 351 of Water. already stated that the galvanic influence is propagated by a polarization of the liquid, as well as the solid, part of the whole circuit. When the two platinum wires are dipped into the acidulated water, the liquid becomes a part of the circuit, and the part cles between the poles become polarized ; so that the atoms of oxygan are all turned towards the positive, and the atoms of hydrogen towards the negative pole, in the manner represented in Fig. 163. On the right, the polarized platinum wire, P, connected with the 163 - zinc end of the battery, z, enters a vessel of acidula- ted water, represented in section. On the left, a similar platinum wire, P, connected with the copper end of the battery, enters the same vessel of water. The polarized wire, P z, on theright,is then the negative po^ of the battery, and the polarized wire, P c, is the positive pole. In consequence of the highly excited negative electricity accumulated in p z, all the atoms of hydrogen in the chain of particles of water being naturally charged with positive electricity, are drawn towards it ; and all the atoms of negative oxygen are repelled from it, and at the same time attracted towards the positively excited platinum wire, P, c ; on the principle that bodies electrified dif- ferently attract each other, while those electrified similarly repel one another. The next instant, the superior negative excite- ment of the wire completely separates the atom of hydrogen from the atom of oxygen, and as it can not unite with the pla- tinum, it is discharged into the water, and escapes into the air. At the same moment, the negative oxygen at the opposite ex- tremity of the chain is drawn powerfully towards the positive platinum wire, and as it can not unite with the platinum, it is also discharged, and escapes into the air. This necessitates a movement throughout the whole chain, and a flow, in opposite directions, of the two gases, and also of the negative and posi- tive current. It is obvious, from the figure, why it is necessary that the positive pole should be made of some unoxidizable metal ; if it were no^, tho oxygen discharged upon it would unite with it to form a solLl oxide, and there would be no escape 365. Describe Fig. lf>3. Show that the decomposition of the water depends upou the polarization of tV circuit. Why is the water acidulated? 15 352 THE DECOMPOSITION OF METALLIC OXIDES "< of gas. Jf the oxide be insoluble, it may adhere to the pole, forming a crust upon it ; in this case, if the oxide be a cor due! or of electricity, it will itself become the pole ; if it be not a < on- ductor, it will interfere with, and finally arrest the course of che current, and put an end to the decomposition. If the oxide be soluble, it will be dissolved as fast as formed, and the water will become a solution of the oxide. If the water contain acid, the acid will unite with the oxide to form a new substance, and the liquid will become a solution of this substance. In tie experi- ment just described, the sulphuric acid is not ifrelf cleeompored, but it tends to favor the passage of the current through the water. It is exceedingly difficult for the electrical current to pass at all through pure water, but on adding from one to fifteen per cent, of acid, its passage is greatly facilitated. Common salt, dissolved in water, produces the same effect. These sub- stances all seem to act by lessening the affinity which binds the part'cles of oxygen and hydrogen to each other. 366. The decomposition of other compound U.quids. Water is not the only substance susceptible of electrical decom- position ; a large number of compound liquids may be decom- posed in a similar manner. It is always necessary that the sub- stance shou'd be a liquid, or soluble in a liquid, otherwise there can be no transfer of the elements which it conta : ns on account of their immobility. If water be solidified, it immediately ar- rests the passage of the current. A sold sub tan ce can not be decomposed in this manner ; but sometimes, merely moistening a solid, will be sufficient to allow the transfer of its elements. Binary compounds, or those which consist of one atom of each element, are those which are most readily decomposed, as is seen in the case of water. In like manner, chloro-hydric acid, a compound substance, composed of chlorine and hydrogen, and whose symbol is HC1, is readily polarized and decomposed by the electrical current ; the chlorine being discharged at the posi- tive pole, and the hydrogen at the negative. Ammonia, com- posed of nitrogen and hydrogen, and whose symbol is NH 3 , is also easily decomposed, the nitrogen collecting at the positive pole, and the hydrogen at the negative. 367. The decomposition of Bffietallic Oxides in solution. Oxygen unites with most of the metals to form a new class of substances called oxides. Thus, common iron rust is a com- 3G6. Why must the compound substance to be decomposed be in the liquid state ? Mention various compound liquids which may be decomposed by the current. 567. De- scriU; tut- decomposition of tae metallic oxides, potash and soda. AND SALTS. 353 / pound of iron and oxygen ; soda is a compound of the metal sodium and oxygen ; potash is a compound of the metal potassium and oxygen. Many of these oxides are soluble in water, and some of (hern can be decomposed by the galvanic current. In all these case^ the metal appears at the negative, and the oxy- gen at the positive pole. Thus, if perfectly pure potash, moist- ened, and placed upon a platinum plate, connected with the negative pole of the battery, be touched with a platinum wire connected with the positive pole, small metallic globules of pure potassium will be formed upon the platinum plate, and oxygen will be discharged upon the wire. The same is true of soda and sodium. If the platinum be formed into a cup, and filled with mercury, and the potash be placed upon it, the potassium amalgamates with the mercury as fast as formed, and may l}e obtained pure by distillation in an atmosphere of nitrogen. 353. The decomposition of Metallic Salts in Solution. The metallic oxides are capable of uniting with acids, to form a class of substances called salts. Thus potash, or the oxide of potas- sium, can unite with sulphuric acid, to form the sulphate of potash. In like manner, the oxide of copper can unite with sulphuric acid, to form the sulphate of copper ; the oxide of lead can unite with acetic acid, to form the acetate of lead; the oxiJe of silver with nitric acid, to form the nitrate of silver. These salts, if dissolved in water, can often be decomposed by the galvanic current, and in all cases, the acid appears at the positive, the metallic oxide at the negative pole ; sometimes, however, the oxide itself is also decomposed, and then its oxy- gen joins the acid, and appears at the positive pole, while the metal alone appears at the negative pole. 369 The Decomposing: Tube. These decompositions can be very clearly shown by the apparatus represented in Fig. 1 64. It is a glass tube, curved twice at right angles. The liquid, or solution to be decomposed, is poured into it, and the poles in- serted, one in each leg. They should be of platinum, and long enough to reach the curve, so as to come as near as possible with- out touching. On pouring into such a tube, technically called a U tube, a solution of sulphate of soda, mixed with a little tincture of blue violets, the salt will be decomposed. The sul- phuric acid will be di-charged at the positive pole, and will change the blue color of the solution to red ; while the soda will 368 Describe the decomposition of metallic salts. At which pole does the acid appear? At which the oxide ? 3fJ9 Describe the decomposing U tube, and the experiments that may bu performed with it. 354 THE DECOMPOSING TUBE. Decomposing U Tube. 164 be collected at the negative pole, and will change the blue color of that tube to green. On disconnect- ing the wires from the battery, and agitating the tube so as to mix the two colors, the original blue will be restored. If sulphate of copper be introduced, the sulphuric acid will be discharged in one leg and the oxide of copper in the o.her. If a solution of nitrate of silver be introduced, the nitric acid will be discharged at one pole, and the oxide of silver at the other; if acetate of lead be employed, the acetic acid, and oxygen from the oxide, will appear in one tube, and the pure lead in the other. If a solution of iodide of potassium be used, the iodine will appear in the positive tube, and the potassium in the nega- tive , and the presence of the iodine may be detected by pouring in a little' solution of starch, which will at once be turned to a deep blue ; the potassium will be immediately converted into potash by uniting with the oxygen of the water, and its pres- ence may be shown by pouring in blue tincture of violets, which will at once be changed to a bright green. The same apparatus will answer equally well for the decomposition of chloro-hydric acid ; the chlorine will appear in the positive tube, and may be detected by its odor and bleaching effect upon a few drops of solution of indigo, and the hydrogen will appear in the negative tube. In like manner, if acidulated water be introduced, the oxygen will be discharged in the positive tube, and the hydrogen in the negative ; and if the end of the leg be stopped with a cork, through which passes a tube of glass, drawn to a fine aperture, the hydrogen, as it escapes, may be lighted, and will burn at the end of the tube with a small, but a steady flame. 370. Glass Cup with Porous Diaphragm. The same ex- periments may be well performed with the apparatus delineated in Fig. 1G5, Jt consists, simply, of a glass cup, divided in the middle by a porous diaphragm of plaster, confined in a frame, as represented in a. This porous diaphragm, inasmuch as it allows the penetration of liquids, and therefore of the establish- What is the effect when sulphate of soda is decomposed ? Iodide of potassium ? fhlo- ro-hydrjc acjd? Water? HOW may the hydrogen be burned? 370. Describe the de, composing cell, and the experiments which may be performed with it. SECONDARY 355 165> ment of a chain of liquid particles through it, offers no obstacle to the pass- age of the electric current, and the con- sequent transfer of Ceil. elements in both di- rections through it. In the decomposition of salts into acids and oxides, the acid will, in all cases appear at the positive, and the oxide at the negative pole, and be manifested, one in each cell. The presence of the acid may bs detected by pouring into the positive cell some tult is explained as in the two previous cases by polarization, the only difference being that the acid, when it strikes the baryta, in the cup B, forming an in-oluble sulphate of baryta, can no longer transmit the current, no solid substance being able to do this, (see 366,) and is immediately precipitated out of the line of voltaic influence to the bottom of the vessel. 37 J. The successive action of the same current on different vessels of water. In Fig. 168, if 1, 2, 3, 4, be a row of glass 1234 Tke action of one Current upon different Vessels of Water. cups containing acidulated water, and g h, ef, c d, a"h, be slips of platinum, joined by wires, on forming the connection with the battery, oxygen will be discharged at the left hand slip, in each cup, and hydrogen at the right hand slip, and in all the cups at the same instant ; and this will continue as long as the current passes. It is plain, from this, that there is a posi- tive and negative pole formed in each cup, and not simply in 375. What is the successive action of the current on the four vessels of water shown in Fiy. 138 ? How many poles are formed in each cup ? How may this be explained by Fig. 169? 15* 360 THE SAME CURRENT ON DIFFERENT VESSELS. the two extreme cup?. Thi* experiment shows, conclusively, that there is a state of polarization extending through the en- tire circuit. Thus, in Fig, 169, on the extreme right may be seen a wire of Fig. 169. platinum, polar- o H o ii OH i zec * l)V tn e action z f the current; the connecting wires are also polarized, as well Uecoinposiuon effected by tne rtiMrization of tue the ^ ire COIHiect- Entire Circuit. CQ With the pOSl- tive pole. As poon as the current passes, the positive electricity moves towards the risrht, and the negative towards the left, and in doing ?o, the hydrogen particles are necessarily drawn in one direction, and the oxygen in the other, at the points where the wires en er each cup. In all cases where the metallic circuit is broken by the intervention of ct liquid conductor, composed of two ele- ments, two poles will be formed at each break, corresponding in position with the poles at the extremities of tl e series, and with the poles of the battery, and at each break decomposition takes place. 376. The successive action of the same current on vessels containing different compound liquids. If we take a series of four cups, arranged as before, Fig. 1 G8, except that a piece of card, or three or four folds of blotting paper, are placed inside the cups, between the slips of platinum, and then introduce into 1, a solution of iodide of potassium, mixed with solution of starch, and into 2, a strong solution of chloride of sodium, co^red blue by sulphate of indigo, and into 3, a solution of nitrate of ammonia, colored blue with tincture of purple cabbage, and into 4, a solution of sulphate of copper, and finally connect with the battery, we shall have iodine set free at the positive pole in 1, shown by changing the starch blue ; chlorine set free at the same pole in 2, shown ty its bleaching the vegetable blue ; nitric acid set free in 3, shown by its reddening the vegetable blue ; sulphuric acid in 4. On the other hand, at the negative pole in 1, we shall find potash ; in 2, soda ; in 3, ammonia ; in 4, oxide of copper. These different substances are attracted towards their respective poles from the fact that they are themselves possessed, naturally, of the opposite kind of electricity. The iodine, chlo- 376. What is the successive action of the same current on various compound liquids 1 ELECTRO-NEGATIVE AND POSITIVE BODIES. 361 rine, nitric acid, and sulphuric ac'd, are naturally charged with positive electricity, and the potash, soda, ammonia, and oxide of copper, wiih negative electricity. All the chemical elements seem to possess a definite electrical character, and this has led to their division into positive and negative electrics. Those are called positive electrics which appear at the negative pole in any decomposing cell, and those negative which appear at the positive pole, on the principle that oppositely electrified bodies attract each other. 377. Electro-Negative Bodies. 1. Oxvgen. 8. Selenium. 15. Antimony. 2. Sulphur. 9. Arsenic. 16. Tellurium. 3 Nitrogen. 10. Chromium. 17. Columbium. 4. Chlorine. 11. Molydenum. 18. Titanium. 5. Iodine. 12. Tungsten. 19. Silicon. 6. Fluorine. 13. Boron. 20. Osmium. 7. Phosphorus. 14. Carbon. 21. Hydrogen. 378. Electro-Positive Bodies. 1. Potassium. 11. Zirconitun. 21. Bismuth. 2. Sodium. 12. Manganese. 22. Uranium. 3. Lithium. 13. Zinc. 23. Copper. 4. Barium. 14. Cadmium. 24 Silver. 5. Strontium. 15. Iron. 25. Mercury. 6. Calcium. 16. Nickel. 26. Palladium. 7. Magnesium. 17. Cobalt. 27. Platinum. 8. Glucinium. 18. Cerium. 28. Rhodium. 9. Yttrium. 19. Lead. 29. Indium. 10. Aluminium. 20. Tin. 30. Gold. 379. The law of chemical decomposition by the electrical current. Mr. Faraday has demonstrated the following law of chemical decomposition by the current. When the same cur- rent acts successively upon a series -of solutions, as in Fig. 1 68, the weights of the elements which are set free at each pole are in the same proportion as their chemical equivalents. Thus, 1 being the chemical equivalent of hydrogen, and 8 the equivalent of oxygen, when water is decomposed, the proportion of hydro- gen to oxygen produced, is always as 1 to 8. The chemical equivalent of potassium being 40, while that of oxygen is 8, in the decomposition of the oxide of potassium or potash, the pro- portion of potassium, by weight, to the oxygen, is always as 40 to 8. Consequently, when a current of electricity is passed through a series of cups, charged with different compound liquids, as in Fig. 1G8, the weight of the different elements set free at the poles in each cup, is not equal, as might be supposed from the equality of the force which acts upon them, but varies according to the chemical equivalent of the element. If cup 1 377. What is meant by electro-negative bodies ? Which is the most highly electro-nega- tive body ? 378. What is an electro-positive body ? Which is the most highly electro- positive body ? 379. State Faraday's law of chemical decomposition. Explain this law by the atomic theory. 362 THE VOLTAMETER. contain water, cup 2 chloride of sodium, cup 3 iodide of potas- sium, cup 4 chloro-hydric acid, while the weight of hydrogen set free in cup 1 compared to that of oxygen, is as 1 to 8, the weight of the elements set free in cup 2 is not the game, but as 35.5 of chlorine to 23 of sodium; in cup 3, it is 127 of iodine to 40 of potassium ; in cup 4, it is 35.5 of chlo- rine to 1 of hydrogen. The reason of this is, that the atoms of the elements differ in weight according to these numbers, and when two substances unite, they do so atom to atom. It fol- lows, as a consequence, that when these atoms are separated from each other, the weights of the elements produced are always those of their atoms ; in other words, of their chemical equiva- lents. This will become clearer hereafter. 380. The amount of zinc dissolved from the generating- plate is always proportioned to the amount of chemical decom- position produced, and vice versa. Not only is this true in respect to the decomposition effected by the current, after it leaves the battery, but also in reference to the chemical action within the battery itself. Thus, for every 9 grs. of water, con- sisting of 8 grs. of oxygen, and 1 gr. of hydrogen, that are de- composed by the electrical current, in cup 1, Fig. 168, exactly 32.7 grs. of zinc have united with 8 grs. of oxygen, and been dissolved in the acidulated water of each cup of the battery. And on the contrary, if 32.7 grs. of zinc have been dissolved in each cup of the battery, it will be found that the electrical current has decomposed exactly 9 grs. of water in cup 1, and set free 8 grs. of oxygen, and 1 gr. of hydrogen. If a smaller amount of zinc has been dissolved, a less amount of electricity has been produced, a less amount of acidulated water decom- posed in the cells, and a less amount of the various solutions in the cups outside of the battery. The amount of decomposition effected becomes, consequently, a measure of the strength of the electrical current. Upon this principle depends the action of the voltameter. 381. The Voltameter. This is an instrument invented by Mr. Faraday, for the purpose of determining the voltaic power of any circuit. It consists of an upright glass cell, having a bent tube, c, fitted into its upper part by accurate grinding; Fig. 170. This tube is curved in such a way as to dip beneath the edge of the carefully graduated jar, d, which is entirely 380. Is there any proportion between the amount of zinc dissolved in the interior of the battery, and the amount of chemical decomposition effected outside of it ? State the proportion of zinc dissolved, and of water decomposed. 381. Describe the voltameter. JIow may it be used to indicate tlie force of tlie current ? ELECTRO-PLATING. 3G3 Tiie Voltameter, 170. filled with water. With- in the glass cell two plati- num plates are arranged, H, connected with the negative pole of the bat- tery, and o, with the posi- tive. The cell is then entirely filled with acid- i^ated water, and aho the bent tube, c. The instrument is then connected with the battery by means of the wires, and made to form a part of the circuit ; the acidulated water in the glass cell imme- d ately be^iiH to be decomposed, and the gases produced are conveyed by the bent tube to the graduated jar, d, by which their volume is measured. The volume produced is in propor- tion to the strength of the current, and the amount of zinc dis- solved within the battery, and thus this instrument becomes a measure of voltaic intensity. 382. Electrc-Platingr and Gilding-. A very important ap- plication is made of these facto in the arts. It will be recol- lected that in all the cases of decomposition of metallic solu- tions mentioned above, the oxide of the metal is deposited around the negative pole, the acid at the positive pole. If, then, any metallic article be attached to the negative wire of the bat- tery, it becomes in effect the pole of the battery, and might be expected to benome coated with the metallic oxide in question; and so it would be, if it were not, that at the same time, with the metallic salt, a small portion of the water is also decomposed, an 1 its hydrogen appearing at the negative pole at the same moment with the metallic oxide, decomposes it, unites with the oxygen to form water, and sets the metal free, as in the case o ' rli-.i cooper ; see Fig. 1 G6. The article attached to the negative pola consequently becomes coated with a covering of metal, in- stea 1 of a metall c oxide. The nature of the metal deposited will depend upon the metallic solution employed. If it be a 332. State the principle of electro-plating arid gilding. 364 ELECTROTYPING. solution of silver, the article attached to the negative pole will become coated with silver; if it be a solution of gold, with gold ; if it be copper, with copper. It is evident, also, that while hydrogen is set free at the negative pole, a corresponding amount of oxygen must escape from the positive pole. 383. Electrotyping-. In order, therefore, to coat or gild sub- stances which are good conductors of electricity, with any metal, it is only neces?ary to attach them to the negative pole of a bat- tery in full operation, and place them in a solution of the metal desired, the positive pole being introduced into the same solu- tion, at a little distance from it. A small battery is quite suffi- cient, and in general one cup of Bunsen's arrangement will answer for all common purposes. The process is fully repre- sented in Fig. 171, where o is the battery; c is the vessel con- Fig. 171. Electro -Plating. taming the metallic solution, which in this case is the sulphate of copper ; D is a metallic rod connected with the positive pole, and having a plate of copper suspended from it, and dipping into the liquid ; B is another metallic rod, connected with the negative pole of the battery, from which the articles to be cov- ered with copper are suspended. Thus, these articles are ma^e the negative pole of the 'battery, and the copper plate suspended from D becomes the positive pole. The connections being formed, the sulphate of copper is decomposed into sulphuric acid and the oxide of copper ; at the same time, a portion of the water of the solution is decomposed into oxygen and hydro- gen. The sulphuric acid and the oxygen are drawn towards ' 383. Describe the electrotype process. THE PROTECTION OP 365 the positive pole, which is the copper plate suspended from D, and the oxygen immediately uniting with it to form the oxide of copper, this is immediately taken up by the sulphuric acid, converted into the sulphate of copper, and then dissolved in the solution, so that just as much copper is thus restored to the solu- tion as is taken from it by the action of the current ; . and its strength sustained for an indefinite period. On the other hand, the oxide of copper, and hydrogen, are drawn towards the nega- tive pole, which is the article, or articles, suspended from the rod B, and here the hydrogen uniting with the oxygen of the oxide to form water, the metallic copper is deposited. In this m:inner, exact copies may be made of all metallic articles. If the article be a copper medal, and it be desired to get an exact copy of it, every part, except the face, to be copied, is covered with wax, and it is then suspended from the rod B, in the sul- phate of copper solution ; it thus becomes completely covered with metallic copper upon the exposed surface ; the thickness of the deposit will depend upon the duration of immersion. On removal from the solution, the deposited copper will tightly adhere to the original metal, but it may be separated from it by gently heating with a spirit lamp. The cast thus formed is the reverse of the medal, and if it be desired to obtain a copy in relief, it is only necessary to subject the cast to the same pro- cess, by attaching it to tho negative pole of the battery, and immersing it in a solution of sulphate of copper. In this man- ner, faithful copies may be made of all metallic articles, by de- positing metals upon them. The finest line engravings may be accurately reproduced. All the copper plates of the coast sur- vey are formed by this process ; the originals are never used, but only the copies, and any required number of these may be produced at a small expense. When the articles to be cov- ered are not metallic, it is necessary to cover them with a fine powder which is a good conductor of electricity, and then treat them in the usual manner. The substance most commonly used for this purpose is plumbago, in very fine powder. The ele-trotype plates from which books are printed, are made by taking an impression in wax, of the original types ; covering this plate of wax with a coating of plumbago, and immersing it in a solution of sulphate of copper, wkh an attachment to the negative pole of a battery. Oa the po itive pole a large plate of copper is suspended, which is gradually dissolved at the same rate as the copper is deposited upon the wax, and the strength of the solution is thus maintained, until the whole plate has 366 COPPER SHEATHING/ disappeared. The powdered wax receives a deposit of copper upon the whole of its surface, "and in its finest lines, which gradually increases in thickness until it is strong enough to be separated fvom the wax, mounted upon wood or metal, and used for printing. The wax may be melted into a new sheet, and applied .to another portion of types. This is by no means the only application in the arts. Gilding, silvering, bronzing, may all be accomplished by it, and it has grown to be a very impor- tant branch of industry. 334. The protection of the copper sheathing- of Ships- By an ingenious application of the same principles the metals can be protected from the action of corrosive liquids in which they may be immersed. Thus, a zinc plate, placed in dilute sulphu- ric acid, will decompose the water with great rapidity, and itself be quickly oxidated, and finally dissolved. If, however, the plate of zinc be attached to the negative pole of a battery, and thus rendered negatively electric, at the same time that a slip of platinum, attached to the positive pole, is placed in the liquid immediately opposite, it will not decompose the water, will suf- fer no oxidation, and remain undissolved. The reason is, be- cause the oxygen of the water is itself a negative electric, and therefore repelled from the negative zinc ; for the same reason the acid is also repelled. In like manner, copper will rapidly decompose chloro-hydric acid, forming chloride of copper, and finally be itself wholly dissolved ; but if the copper be rendered negatively electric, it will remain unaffected by the acid, because chlorine is also a negative electric, and is repelled from a body which is charged with electricity of the same kind. In this way it is possible to protect metals by means of galvanic ar- rangements from the influence of the most corrosive liquids. Sir H. Davy made an ingenious application of this principle to the protection of the copper sheathing of ships from the action of eea water. Sea water contains in solution a variety of metal- lic salt?, the most important of which is chloride of sodium, or common salt. The chlorine contained in this substance has a very strong affinity for copper, and will attack it with great vio- lence, forming a green chloride of copper, which is at once dis- solved by the water, and thus the copper is rapidly wasted. Chlorine, however, is an electro-negative substance, and if the copper sheathing could be rendered also electro-negative, it 384. How may the metals be prevented from corrosion by the action of the electro- negative elements, such as oxygen, and chlorine? On this principle, how may the copper sheathing of ships be protected 1 What disadvantages have arisen from this protection ? MAGNETIC EFFECTS OF THE CURRENT. 367 r would be repelled, instead ot attracted, and the metal would ba perfectly protected from corrosion. This can b3 done by driv- ing zinc nails into the copper, at proper intervals. The zinc at once becomes electro-positive, attracts the chlorine to itself, and sets 01* foot an electrical current, which is transferred to the copper ; it thus becomes the generating plate of a battery, while the copper becomes the conducting plate. The copper is thus made electro-negative, and tends as strongly to repel the chlo- rine as the zinc does to attract it. By this arrangement, copper sheathing is completely protected, and kept entirely free from corrosion ; but unfortunately, at the same time that the chlorine is repelled, other substances, such as lime and magnesia, being electro-positive in their character, are attracted to the copper. This earthy coating furnishes good points of attachment to sea weeds and shell fish, which soon make the bottom of ships very foul, and greatly impade their progress, It has become neces- sary, therefore, to discard the invention, and the same end is now partially attained by the use of a kind of brass sheathing, com- posed of zinc and copper, and called Muntz's yellow metal. On the same principle, metallic structures, such tts iron pillars, fen- ces, and the like, niy be protected from atmospheric action by the insertion of small bits ot zinc, at regular intervals. There are other applications of the same principles possessed of nearly equal interest, III, Magnetic effects of the Current. The power of light- ning in destroying and reversing the poles of a magnet, and in. imparting magnetic properties to pieces of iron which did not previously possess them, has been known for a long period, and led to the opinion that similar effects might be produced by the common electrical machine, and the galvanic battery. No re- sults of importance were obtained, however, until the year 1819. In the winter of that year Professor Oersted, of Copen- hageri; discovered that if a magnetic needle be brought near a copper wire, connecting the two poles of a battery, and through which the electrical current is passing, the needle is at once violently agitated, deflected from its position, and made to as- 385. What effect is produced upon the magnetic needle by a wire carrying the current, placed parallel to, and above, it ? 368 THE MAGNETIC NEEDLE DEFLECTED. S ^ ,. sume a position at right angles to the wire. Thus, if the wire be placed upon the magnetic meridian, pointing north and south, the north end connected with the negative pole or zinc plate of the battery, and the south end connected with the positive pole, or the platinum plate of the battery, and the magnetic needle be placed below the wire, it will at once assume a position at right angles to the wire, the north pole moving to the west, and the south pole, to the east, as represented in Fig. 172. If the needle be placed above Fl "* 172< the wire, the north pole will move to the east, and the south pole to the west. When the needle is placed in the same hori- zontal plane with the wire, it attempts to assume a vertical position, the north pole dipping when the wire is to the west of it, and rising when the wire is to the east of it. If the current be reversed, by changing the connec- tions with the battery, and be made to pass from north to south, instead of from south to north, the movements of the needle are all reversed. The explanation given of these movements is, that two magnetic forces are generated by the passage of the current, circulating around the wire in opposite directions, along its whole extent, and at right angles to it ; the tendency of one force is to cause the north pole of the needle to revolve around the wire in one direction ; the tendency of the other is to cauee the south pole to revolve in like manner in the opposite direction ; the magnet, consequently, comes to rest in a position of equilib- rium between these two forces, directly across the wire. Besides this directive action upon the magnet, the conducting wire also exerts an attractive action, as may be shown by suspending a magnetized sewing needle from a silk thread, and causing an electrical current to pass in an horizontal direction by the side of, and very near it. It also exerts an inductive-magnetic action, by which soft iron wires, or bars, placed across the conducting wire at right angles, are rendered magnetic as long as the cur- By a wire placed below the needle ? If t'.ie current be reversed, what is the effect upon the needle ? Whr.t i.* t"ie explanation given of these movements? What other magnetic elfects are produced by the current? Effects of Galvanic E'frtricity on the Magnetic Needle. THE MAGNET DESCRIBED. 369 r rent circulates. The action of the conducting wire is, there- fore, threefold. 336. What is a X&ag-net? A magnet is a body which possesses the power of attracting masses of iron, and a few other metallic substances, such as nickel, cobalt, and chromium. They are distinguished into natural and artificial. The natural magnet is an oxide of iron, first found in Magnesia, a district of Asia Minor, and from this has received its name. Artificial magnets are bars, or needles, of tempered steel, which do not naturally possess the properties of a magnet, but have acquired them by friction with another magnet, by the action of electri- city, or by percussion in the magnetic meridian. They are more powerful than natural magnets, and possess identical prop- erties. The attractive power of magnets is exercised at all dis- tances, and through all bodies, but decreases with the distance, and varies with temperature ; at a red heat, magnets lose their attractive power altogether. 387. The poles of the Mag-net. The attractive force of the magnet does not reside equally at all points upon its surface ; this may be clearly shown by holding a magnet immediately over iron filings placed upon a sheet of paper, when the filings will be seen to accumulate equally at the ends of the bar, while they will not be attracted at all at the middle ; Fig. 173. These two ends, at Fi S- i^ 3 - which the force resides, are called the poles of the magnet. Eve- ry magnet The Magnet. pOSSCSSCS two poles, as one can not exist without the other. If a magnet be suspended upon a pivot, it will place itself very nearly upon a meridian line, and one pole will invariably point towards the north, and the other towards the south ; if it be moved from this position, in a few moments it will resume it, the same pole pointing to the north as before ; hence one pole of the magnet is called the north, and the other the south pole. 388. The mutual action of the Poles. The two poles at- 335. What is a magnet ? What is the origin of the name ? What are artificial mag- nets ? What is the effect of a, red heat on a magnet ? 387. Does the attractive force of the magnet reside equally at all points on its surface ? What are the poles of the mag- net ? 388. State the difference betwa 3 a the polar forces of the magnet. 370 THE DIRECTIVE ACTION OF THE EARTH. 174, tract iron filings equally, and appear to be identical in tliefr character; but in fact they possess different kinds of magnetism, endowed with properties opposite, but analogous to each other. Thus, if a small magnetic needle, Fig. 174, be suspended from a fine thread, and the north pole of a second needle be presented to the north pole of the first, a quick repulsion takes place ; but if the same north pole be presented to the south pole of the suspended needle, attrac- tion immediately takes place. The poles, n and s, are not then identical, since one is repelled, and the other attracted, by the same pole, N, of the magnet held in the hand. If the south pole of the second magnet be in turn presenled to the north pole of the first, attraction will take place ; and on the other hand, if presented to the south pole of the first, repulsion will ensue. Consequently, we deduce this principle, that magnetic forces of the same kind repel, and those of different kinds attract, each other, These t\vo magnetic forces are always developed at the same time ; one can not be produced without the other ; they are equal in amount, are opposite in their tendencies, and are capable of exactly neutralizing each other. Forces which exhibit this combination of equal and opposite powers are called polar forces. Electricity is also a polar force, and the analogy between it and magnetism, is so complete that it is obvious they must be closely connected. 389. The directive action of the Earth upon Mag-nets. It has been stated that if a magnetic needle be suspended by a thread, or supported upon a pivot, on which it can readily turn, it will oscillate for a time, and finally take a position nearly n< rth and south. If the needle be placed upon a cork, in a Mutual action of Magnetic Poles. "".'ha-t prinfinle do we deduce from these facts ? What are polar forces? 389. What is tae eflect of tae earth upou u magnetic needle? THE ASTATIC NEEDLE. 371 s. The directive action of the Earth. vessel of water, the same thing takes place ; it assumes a posi- tion north and south, but does not advance either to the north or south. The action of the poles of the eurth upon the mag- net is not attractive, but directive, as though these poles were situated at an immense distance. Fig- ITS- The earth appears to be a vast $ magnet, whose poles are situated near the poles of the earth, the north magnetic pole being within the arctic, and the south mag- netic pole within the antarctic circle. Consequently, as mag- netic poles of the same kind re- pel, and of different kinds attract, each other, the pole of an artifi- cial magnet which points towards the north pole of the earth must be its true south pole, and the pole which points towards the south pole of the earth its true north pole. Fig. 175. 390. The Astatic Needle. The astatic needle is a magnetic needle, arranged in such a manner that it is no longer under the directive influence of the magnetic poles of the earth, and con- sequently, will remain fixed in any position in which it may be placed, without tending to point north and south. Two mag- netic needles are placed, one beneath the other, and fastened firmly together by a pin, with their poles reversed, i. e., the north pole of the upper needle having the south pole of the lower needle directly be- neath it, and the south pole of the upper nee- dle having the north pole of the lower ar- ranged likewise. Consequently, the attraction which the north pole of the earth exerts upon the upper needle is counteracted by the repul- sion which it exerts upon the south pole of the needle fixed beneath it; the compound needle is therefore not drawn towards the north ; for the same reason, it is not drawn The Astatic Needle. towards the south, but remains indifferently in any position in which it is placed, without at la the aetion attmrtivp, or directive ? What is the true north pole of the needle ? Tli true south pole? 390 Describe the astatic needle. iff. 176. 372 THE INDUCTION OF MAGNETISM. the same time losing any portion of its magnetic power ; hence its name, derived from the Greek, which means unsteady, havii g no directive tendency. 391. Induction of XVZagnetism. A powerful magnet has the power of inducing magnetism in magnetizable substances placed near it, in the same way as a highly charged electrified body has the power of inducing electricity in all bodies in its vicin- ity. Thus, if a piece of iron be brought near the north pole of a powerful magnet, but not touching it, the end of the iron nearest the magnet will be affected with the opposite, and the remote end with the same, magnetism ; consequently, the iron being thrown into the opposite magnetic state, will be attracted towards the magnet. This is the cause of all magnetic attrac- tion, and is due to the magnetism induced in the body attracted ; in the cae of iron filings, each particle becomes magnetized. If, while the piece of iron is under the inductive influence of the magnet, another piece of iron be presented to it, and to this another, these pieces will all be magnetized by induction, with their poles reversed, and be attracted by the first piece ; Fig. 177. If the magnet be removed, the induced magnetism of all Fisr. 177. i Induction of Magnetism, the pieces of iron is destroyed, and they will fall to the ground ; this induction is not prevented by the interposition of unmag- netizable substances between the magnet and the iron ; a piece of glass inserted between them will not interfere with the effect. 392. All substances are either attracted or repelled by the Magnet. Magnetic and Dia- magnetic Bodies. It was formerly supposed that iron was the only substance susceptible of attrac- tion by the magnet ; it was afterwards proved that the metals, nickel and cobalt, are also possessed of the same susceptibility, and more recently it has been discovered that all bodies are 391. What is meant hy the induction -of magnetism? How can it be proved? 392. What is the difference between magnetic and diamagnetic bodies ? What other metals, besides iron, are susceptible of magnetization ? MAGNETIC AND DIA-MAGNETIC BODIES. 373 Fig. 178. Tlie Mtigiuiic Field. Fig. 179. affected by the magnet, in some degree, and either attracted or repelled by it. Thus, if, in Fig. 178, N and s represent the poles of a powerful horse-shoe magnet, upon which the observer is looking down ; the line A, x, connecting the two poles, may be called the axis of the magnetic field, and E, Q, which crosses it at right angles, its equator. If an iron needle be sus- pended by its centre, above such a magnet, it will take a horizontal direction, parallel to the axis A x, and is sail to point axially. But if a stick of phosphorus be suspended between the two poles of the magnet, it will take the equatorial position, E Q, the phosphorus being re- pelled by each pole to the great- est possible distance ; consequent- ly, phosphorus is called a dia-mag- netlc body. Some of the metals, such as antimony and bismuth, exhibit this dia-magnetic property in a still higher degree. It is even possessed by many substances of an organic nature. In Fig. 179, is represented a bar of copper, occupying the equatorial position between the two poles of an elec- tro-magnet, which project upwards through apertures made in the table. While iron is the most highly magnetic of all substances, there are many others not usu- ally esteemed magnetic, which will take the axial position, if brought near the poles of a powerful magnet, such as the red oxide of iron, and even a sheet of writing paper, if rolled into the form of a short cylinder, .will usually, owing to the iron or cobalt which it contains, assume a similar direction. 333. The dia-mag-nctisan of Gases. The property of dia- magnetiam is not confined to solids and liquids ; the gases also What is the axis and the equator of the magnetic field? IIo\v can diamagnetism be illustrated by phosphorus and bismuth? By a sheet of writing paper? 393. How can the magnetism and diamaguetism of gases be shown? The Dia-magnetism of Solids. 374 OXYGEN MAGNETIC. F [g- 18 - possess it. Thus, if three tubes he arranged in the equator of the mag- netic field, as shown in Fig. 180, and in each tube a piece of paper, moistened with chloro-hydric acid, be suspended, and another piece of paper, moistened with ammonia, be placed in a bent tube, conveying 'The D'ta-magnetism of Gases. the gas ill question, tllC gas Will l)C- come charged with ammoiracal va- por, and as long as the electro-magnet is not brought into action, will pass directly up the centre tube ; but as soon as the electro- magnet is in operation, those gases which are dia-magnetic will no longer pass up the centre tube alone, but will enter the side tubes, arranged in the equator of the instrument, and their pres- ence will be made manifest in each tube by the white cloud which is always produced when the fumes of ammonia come into contact with those of chloro-hydric acid. The same fact can also be determined by blowing eoap bubbles with the gas in question, and bringing them near the poles of the magnet ; if attracted, the gas is magnetic ; if repelled, it is dia-magnetic. 394. Oxygen a magnetic substance. By suspending a feebly magnetic glass tube between the magnetic poles, success- ively in oxygen and in vacuo, it has been found that it is le^s strongly attracted in oxygen than in the exhausted receiver, and on varying the experiment in different way-, it has been proved that oxygen is a decidedly magnetic body. A cubic French metre of oxygen, which is rather more than an English cubic yard, and which ordinarily weighs 22015 grs., if it were con- densed until it had a specific gravity equal to that of iron, would act upon a magnetic needle with a force equal to that of a little cube of iron weighing 8^ grs., and the magnetism of oxygen is to that of iron, as 1 : 2647. The magnetic effect of the oxygen in the air is equal to that of a shell of metallic iron ^\-^ of an inch in thickness, surrounding the entire globe. Oxygen loses its magnetism when strongly heated, and recovers it aga r n when the temperature falls. The diminution of its magnetic intensity as temperature rises, has been thought to explain the diurnal , variations of the needle. It has also been ascertained that the j . , 894 How can the magnetism of oxygen be proved ? To what is this magnetic power equal when compared wit 1 ! that of iron? What is the effect of heat upon it? is the flame of candles and the electric light magnetic, or dia-magnetic' EFFECT OF CURRENT ON THE MAGNETIC NEEDLE. 375 flame of candles, and of the electric light, is dia-magnetic when placed between the poles of a powerful imignet. 395. Magnetic and Dia-magnetic Bodies. The following is a list of various substances arranged in the order of their magnetic and dia-magnetic powers as determined by Mr. Fara- day. Magnetic. Iron. Nickel. Cobalt. Manganese. Chromium. Cerium. Titanium. Palladium. Crown Glass. Platinum. Osmium. Oxygen. Dia-magnetic. Bismuth. Copper. Phosphorus. Water. Antimony. Gold. Zinc. Alcohol. Silico-borate of Lead. Ether. Tin. Arsenic. Cadmium. Uranium. Sodium. Rhodium. Flint Glass. Iridium. Mercury. Tungsten. Lead. Nitrogen. Silver. 395. Reason why a Xffag-netic Needle assumes a position at right angles to the Conducting: Wire. From what has been said, it is evident that the magnetic needle assumes a position at right angle.i to the wire connecting the two poles of the battery, because, of the creation of two magnetic forces circulating around the wire in opposite directions, and at right angles to its length ; the north pole of the needle being controlled exclusively by the south magnetic force, and the south pole exclusively by the north magnetic force. A galvanic current can not traverse a wire with- out generating polar magnetic forces, circulating around it at right angles along its entire length. Thus, in Fig. 181, if A, B, rep- resent a wire, through which Fi -- 1P1 - an electrical current is passing, indicated by the dart, the small arrows indicate one of the mag- netic forces, or magnetic cur- Iralvantc Current mcii'tating Magnetic -. Force. rents, as they are sometimes called, which cross it at right angles, and the galvanic current can not be made to traverse such a wire without producing these magnetic forces. Not only does the electrical current generate these polar magnetic forces which cross it at right angles to its length, but it also magnetizes the wire itself. This may be proved by the attraction which it exerts upon iron filings wh n they are brought near it ; if the current be broken, the filings immediately fall. These fiT.ngs are at- 83">. Mention some of fie principal magnetic and diamagnetic bodies. 393. What is the reason that the conducting wire affect.-? the magnetic needle? Does the wire itself become magnetic? How can t.iis be proved? Is it possible for the current to traverse a wire without producing magnetism ? 16 376 ELECTRO-MAGNETS. * traded to the wire by the magnetism which it induces, and as long as they are under its influence they are made temjorary magnets, in the same way as they would be, if acted upon by a powerful permanent magnet. See 3 ( J1. 397. The galvanic current induces Magnetism. Electro- magnets. IS T ot only are iron filings thus induttive'y con- verted into temporary magnets by the wire, but larger pieces of iron, if brought near the wire, are similarly afiechd. If a small rod of iron be placed at right angles across the connecting wire, it will become strongly magnetic, ar.d con- tinue so, as long as the electrical current passes ; if the connec- tion of the wire with the ba'tery be broken, the magneti.-m ceases. If the rod be placed in a small glass tube, and the conducting wire, instead of crossing once at right argles, be carried around it several times, forming a spiral coil, so that the electrical current is made to pass several times around the iron rod, its magnetic power will be greatly increased.. The extremi- ties of the rod will be the poles of the temporary magnet, and this wi.l be the ca?e Fig. 182. even if the extremities of the iron rod project some distance beyond Right Hand Helix. n the coil. Such a spiral coil of wire is called a helix, and when wound to the right, constitutes a right-handed helix, Fig. 182 ; and when to the left, a left-handed helix ; Fig. 183. In the right _ Fiig. 183^ hand helix, the sou ih pole is at the extrem- ity of the coil, at whic h Left Hand Helix. the positive elt ctric current enters it; in the left hand helix, the south pole is always at the extremity, by which the current leaves the helix. If the direction of the current be reversed, the poles will also be reversed. It is not necessary to place the rod of iron in a glass tube ; if the wire be wound with some good non-conductor of electricity, such as silk, or cotton, so as to compel the electrical current to circulate around the rod, without leaping transversely across the wires, or entering the rod itself, the same end will be attained. Such 397. How can a rod of iron be made magnetic by the current? What is a right hand helix? A left hand? How are the poles of each arranged ? What is the eJect upon tae poled of reversing the current ? MAGNETISM INDUCED BY THE CURRENT. 377 a bar of iron, converted into a temporary magnet, by the induc- tive influence of an electrical current, is called an electro-mag- net. If a steel rod be substituted for the soft iron bar, it will become permanently magnetic. The same effect will be pro- duced upon a steel needle placed in the centre of a spiral coil of wire, through which a powerful charge of frictional electri- city from a Leyden jar is transmitted. If a wire, carefully woun I with fine silk or cotton, and thoroughly coated with shell- lae dissolved in alcohol, in order to increase its non-conduct- ing power, be wound several times around the iron rod, proceed- ing regularly from one end to the other and then returning, the magnetic power produced by the circulating current will be greatly increased, and the greater the number of co'ls, the more powerful is the effect. In Fig. 184, is represented a coil of this description, wound into the form of a 184 -___ hollow cylinder, so that the iron rod may be withdrawn at pleasure. If the rod be removed, and the connections established with the battery by means of the binding cups arranged below, it will be found that the ends of the coil have themselves become very strongly magnetic, as shown by their Magnet, Mi'Ie and . L J ,. o f j . JL. TP . Unmade. attraction ot iron filings. If the rod be now inserted, this will become, by induction, very strongly magnetic, and support quite large pieces of iron brought near the poles; these pieces of iron become themselves possessed of magnetic power, and will support additional pieces, so that quite a long chain of magnets may thus be formed in the manner rep- resented in the figure, in all cases the north pole of one being opposite the south pole of the next. If the connection with the battery be broken, so that the battery current ceases to flow through the coil, the magnetism of the rod, and of all the pieces of iron, is at once destroyed, and the keys fall ; if the connection be reestablished, the magnetism is immediately restored, and the keys are again attracted. In this manner, by forming and breaking the connection with the battery, a piece. of soft iron, may be magnetized and de-magnetized at pleasure. If a mag- netic needle be brought near the magnetized rod of a helix, it will be thrown into violent agitation for a few moments, and then have one of its poles strongly attracted towards one of the What is the effect of carrying the wire several times around the iron bar? What is an electro-magnet ? Describe Fig. 184. Ts the coil itself made magnetic by the passage of the current ? How cau an electro-magnet be made and unmade ? 373 THE GALVANOMETER. poles of the rod. If it be the north pole of the needle which is thus attracted, we may know that it pom's to the south pole of the iron rod, and thus the character of its poles may be de- termined. 398. USolecular movements during- the magnetization of Bars. The induction of magnetism, and die cessation of mag- netism, are both attended witji molecular motion throughout the rod of iron. The rod, on becoming magnetic, acquires a si ght increase in length, and suddenly contracts to its former dimen- sions when the magnetism ceases. If the bar be supported at one end, so as to bend under its own weight, it becomes stra'ght- ened to a greater or less extent when magnetized. Each time that the bar becomes magnetic, or loses its magnetism, a distinct sound is produced. Finally, the molecular movements, if re- peated in quick succession by rapidly making and breaking con- tact between the helix and the battery, so as quickly to magne- tize and de-magnetize the rod, produce an elevation of its tem- perature, which is entirely independent of the heat produced in the conducting wire by the flow of the electrical current. These facts are possessed of great interest, as connected with the theory of the convertibility of Forces. (See 263 and 264.) 399. The Galvanometer. The degree of movement in a magnetic needle, produced by the passage of an electrical cur- rent, is proportioned to the streng'h of that current, and may be used, therefore, to measure its intensity. An instrument con- structed for this purpose, is called a Galvanometer. Its use is restricted to the measurement of currents of feeble intensity, because, when the current reaches a certain degree of strength, the needle immediately assumes a position at right angles to the wire, and flies at once to the farthest point to which it can go, and it is evident that it can measure no degree of strength in the electrical current beyond that which will drive it into this position. For the measurement, however, of currents of elec- tricity of low intensity, this instrument is invaluable. It is of two kinds, the common, and the astatic galvanometer ; in the former, a common magnetic needle is employed ; in the latter, an astatic needle. In the common galvanometer, instead of having the wire connecting the two poles of the battery pass once directly above or below the magnetic needle, it is bent, and curried first beneath the needle, and then brought back above 998. Describe the molecular movements which take place during the magnetization of bars ? What effect is produced upon the temperature of the bar by rapid, magnetization, and demagnetization ?-^-399, Describe the common galvanometer. THE ASTATIC GALVANOMETER. 379 The Common Galvanometer. 185 - it, as represented in Fig. 185; in this manner, the effect of the current upon the needle is doubled, and its sensitive- ness to the passage of very feeble cur- rents greatly increased. In the most perfect form of the instrument the wire is carried, not simply once around the magnetic needle, but several times, so as to constitute a longitudinal coil, within which the needle plays freely. When the instrument is to be used, it is placed, with the coil and the needle, in the magnetic meridian ; the connec- tion is then formed, and the electrical current transmitted ; the needle is at once deflected to the east, or west, as the case may be, and more, or less, according to the strength of the current ; when the current exceeds a certain strength, the needle assumes a position at right angles to the coil, and ceases to measure any additional degrees of intensity. 400. The Astatic Galvanometer. In the common galvan- ometer, the needle, when deflected by the electrical current, evidently moves in opposition to the magnetism of the earth, which tends to keep it in the magnetic meridian, and the dis- tance to which it moves is not, therefore, a correct indication of the real strength of the current, but of its force less the amount of the magnetic attraction of the earth. If this attraction be neutralized, its sensitiveness to the in- fluence of the electrical current is great- ly increased. This is accomplished by the use of the astatic needle, which, as has been shown, ( 390,) is constructed in such a way as to be free from this influ- ence, in consequence of the counteraci ing influence of opposite poles. The con- ducting wire is carried, as in the last case, first under, and then above, the lower need'e; Fig. 186. Such a needle is indifferent to the magnetism of the earth, and will remain without change in any position in which it may be placed ; in practice, how- ever, it is arranged so as to tend slightly to occupy a north and The Astatic Galvanometer. 400. Describe the astatic galvanometer. * 380 LIQUID PART OP CIRCUIT EXERTS MAGNETIC ACTION. The Astatic Galvanometer, with Coil of Wire. south direction, in order that it may possess a fixed point from which its motion may be measured. This galvanome- ter is represented in section, in Fig. 187; G is a glass case, protecting the instrument from dust, and currents of air; d is a fibre of silk, by which the needle is suspended ; n s, s n y represent the compound nee- dle with reversed poles ; c, c, is a graduated copper plate, to mark the movement of the upper needle; w, w, is the coil of wire ; b, b, are the bind- ing cups, for making connections ; m, m, are screws for level ng ; and /, a small lever for adjusting the position of the needle upon the graduated copper plate. Such an instrument is sensitive to the feeblest currents of electricity, and will detect that which is produced by two bits of zinc and platinum wire, not half an inch in length, placed in acidulated water. This instrument is invaluable for the measurement of small degrees of heat, as well as of electricity, as we shall see hereafter. 401. The liquid part of. tho voltaic circuit acts upon the Eflagneiic Needle,, That the electrical current, in every part of its course, acts upon the magnetic needle, i. e., in the liquid within the battery, as well as in the wire connecting the poles, may be beautifully seen in Fig. 188. A needle, n, 5, is suspended over a dish of acidu- lated water; on one side of this dish a zinc plate, z, is placed, and on the other a platinum plate, P; the needle must be placed so that one of its poles point to one plate, and the other pole to the other. If the two plates be now connected by a wire, the needle will be deflected, and will place itself nearly Fig. 188. The liquid part of the Circuit magnetic. parallel to the plates. 401. Show that the liquid part of the circuit acts upon the magnetic needle. THE LAWS. OF ELECTRO-MAGNETISM. 381 402. The laws of Electro -magnetism. The following laws have been established in regard to the production of magnetism by the electrical current, so long as the battery current is maintained of uniform strength. 1st. The magnetism induced in any given rod of iron is proportioned to the number of colls of insulated wire which are wound upon the rod ; and it makes no difference whether the coils are uniformly distributed over the whole length of the rod, or accumulated towards .its two extremities. 2d. The diameter of the coils which surround the rod does not influence the result, provided the current be of uniform strength, the effect of increase of distance of the coil from the bar being compensated by the increase of effect produced by the additional length of the wire. 3d. The thickness of the wire has no effect upon the result. 4th. The energy of the magnetism is proportioned to the strength of the current. 5th. The retentive power of the magnet increases as the square of the intensity of the magnetism. 6th. The intensity of the magnetism is proportioned to the surface which the rod exposes ; and in cylindrical rods is as the .square of the weight ; bundles of separate wires expose a larger surface than a solid rod, and hence are susceptible of a higher amount of magnetism than a solid bar of equal weight. 7th. The employment of long rods possesses this advantage over short rods, that the neutralizing influence of the two poles upon each other is lessened. 8th. The increase of magnetic energy by the increase in the strength of the electric current, proceeds up to a certain point, but there is a limit to the amount of magnetic force which can be devel- oped in iron, although the amount of electric action may be indefinitely increased. 403. Ampere's theory of Magnetism. Ampere's theory of magnetism is, that in every magnet there are currents of electricity circulating around it at right angles to a line joining Ampere's Theory of Magnetism. the tw P leS > Fi 9' 189 > Rnd tl){lt these currents are the source of the magnetic force. In the ordinary magnetic needle, which is pointing north and south, these electrical currents ascend on the western side, and descend on the eastern. This theory is .founded upon the magnetic properties possessed by a helix, through which a current of electricity is circulating. If a 402. State the laws of electro-magnetism. 403. State Ampere's theory of magnetism. 382 AMPERE 3 THEORY OF MAGNETIS1F. Fig. 190. The Magnetism of a Wire Helix carrying the Current. simple helix of thin wire be freely sus- pended in the man- ner represented in Fig. 190, by a hook dipping into a cup containing mercury, and supported at the lower end in a simi- lar cup of mercury, as soon as the elec- trical current is made to circulate in a down- ward direction, the he- lix will acquire mag- netic properties, as represented in the figure, and assume a north and eouth posi- tion ; if suspended upon a point, it will assume a position par- allel to the dipping needle. The helix will also be subject to attraction and repulsion by the poles of another helix, similarly mounted, and in short, exhibit all the properties of a common bar magnet; Fig. 191. Hence the supposition that the com- mon magnet is nothing but an iron bar, around which a similar current of electricity is continually circulating. The cause of these currents is not known. The mag- netism of the earth is sup- posed to be produced by currents of electricity circu- lating continually around it from east to west, perpen- TWO Magnetic Helices. dicular to the magnetic me- ridian ; these are thought to be thermo-electric currents, due to the variations of tempera- ture, resulting from the successive presence of the sun upon dif- ferent parts of the surface of the globe from east to west, and by their circulation they produce the north and south On what is this theory founded? Describe the movements of a helix carrying the cur- rent. Show how two mounted helices, carrying the current, affect each other Explain the magnetism of the earth in Ampere's theory. Expbtin how the electrical currents of the earth circulate from east to west, while those of the uiaguet circulate from west to east. Fig. 191. THIS THEORY SATISFACTORILY EXPLAINS 383 magnetic poles of the earth, and give a fixed direction to the magnetic needle of the compass. That these currents circulate from east to we it, while those of the ordinary magnet circulate from west to east, (=ee Fig. 189,) is explained by the fact, that the north magnetic pole of the earth really corresponds with the south pole of th3 ordinary magnet; and if the south pole of the ordinary magnet be turned towards the north, it will be seen that the currents, in this case, Fig. 189, really flow from east to west, just as in the ca~e of the earth. 40 1. The magnetic effect of the wire carrying the galvanic current accounted for by Ampere's Theory. It has been found that when two wires are freely suspended near each other, and galvanic currents are transmitted through them, the wires will repel each other, if the currents pass in opposite directions, but they will attract each other if the currents be in the same direction. If the two wires, moreover, through which the cur- rent is passing in the same direction, be not exactly parallel, but cross each other at an angle, they will tend to place themselves in parallel lines. Now if it be granted that, in every straight mignet, electrical currents are continually circulating in a direc- tion at right angles to a line joining the magnetic poles, we see plainly the reason why a magnet tends to place itself at right angles to a wire connecting the poles of the battery, and carry- ing the galvanic current, viz., that by such a movement the elec- trical currents in the wire, and in the magnet, assume a direc- tion parallel to each other. Let p Q, in Fig. 192, repre ent a wire carrying the galvanic current in the direction of the arrow, and let N indicate the north pole of a bar magnet, around which electrical cur- rents are supposed to be circulating in the same direction as in the wire ; according to the above theory, these electric currents will necessari'y tend to arrange themselves parallel to each other, and the magnet assume a position at right angles to the wire. On the other hand, if the magnet, N, be fixed in an upright position, so that it can not move, and the wire, r, Q, be suspended 404. When the galvanic current is transmitted through the wires in opposite directions, what effect is produced? If in the same direction? If the two wires in the last case be not exactly parallel, what effect is produced? How does this explain, according to Am- pere's; theory, the effect of the wire on the magnetic needle ? 10* 192. P 1 n II ml Q i The magnetic influence of the Wire explained. : 4 tttK MAGNETIC KFfKCT OP THE fVeely parallel to It, as soon as the gnlvnnic current begins to circulate from P to Q, tin; wire will tend to move, and as*urne a position at right angles to the magnet. Tint*, the notion of the magnet and the wire is reciprocal ; they both tend equally to move into such a portion, in reference to each other, that (lie electric currents in both will he parallel, and that one*, of the two, will actually move, which to the leant permanently fixed, That the wire carrying the current doe* actuiilly move, o as to mljn*t iinelf tf) the, magnet, may he nhown by the apparatus in Fig. 100. Let tt plate of zinc, z, be connected by a wire with the cop- per plate, (!, and both be Mirtpcndcd in a little gla?* vewel containing acidu- lated water, which, by the Aid of iv piece of eork, t), ia made to float, in A ve*el of water. In this CAe, the galvanic, current to circulating, as indicated by the arrows, from west to east. If now the north pole of A permanent magnet be presented to the wire, as it* electrical current* are also circulating from Rirts Ktf^, to enst, an<1 are parallel to those of the loop, the liitle bat- tery will maintain its jmMtion, the only effect being, Hint it will be attracted by the magnet, and finally place it< It' midway be- if kWO poles \ but if the south pole of the magnet be pre- i i.. it. tin , i< ,,i ,.il currents of which are rnul.ii n , -I, in llx> reverse dilMiCtion from tboM- of ilu- \MIV. Ilir I. niicl >li" tWOb< ">in< paralltl; .'>,! fm:ill\ \\ill !< Ml I !;.: .1 M . l.rlorr. mil il ii ooeupiw : position mklwt^ between ih- twopo'w* If th- ..-fixmof the r:irlh !)<' j MS wngg*ti'd in il. 1.- t "I. >'li. . - Mr>-li\g urrettt? i THE ACTION OF TIIE WIRE 385 article, by thermo-electric currents circulating around it from east to we>t, perpendicular to the magnetic meridian, it i- evi- d -nt that a win-, carrying the galvanic current, it' freely sus- pended, ought to arrange itself, according to the above princi- ple-;, parallel to these currents, and at right angles to the mag- netic meridian. This i-^ found to be the case, and it constitutes a remarkable confirmation of the truth of Ampere's theory. If the curved wire, Fig. 194, be suspended from mercury cups, \ ' the magnetism of the Earth, upon the icire carrying Ike. Currint. so that it can move freely, and be turned so that its plane coin- cities with the magnetic meridian, it will remain in that position until a connection is formed with the battery, and a. current p:i eil through it. When this takes place, it will be seen to turn slowly around the pivots, so as to take a position at right angles to the magnetic meridian, and parallel to the thermo- electric currents supposed to be circulating from east to w.-st. It will turn in such a direction that the current in the lower part of the hoop will also be from east to west. Other rota- tions, of a similar kind, may be explained upon the same theory, but it is not necessary to pursue the subject farther. -The main fa 't is, that the galvanic current, traversing a wire, pro- duces magnetic forces on lines at right angles to its length, and induces magnetism in a bar of soft iron placed across it perpen- dicularly. Explain Fig. Wi. What is the main fact .' 386 AND THE MAGNET RECIPROCAL. Horse Shoe. Electro- Magnet. 196 - Fig. 195. 405. The most powerful form of Electro- BZaguets. Horse-Shoe Blag-nets. By increas- ing the number of coils upon a straight rod of iron, its magnetic power may be indefinitely increased. But the best mode of arranging magnets of this kind is to bend the iron bar into the form of a horse-shoe, as shown in Fig. 195, and then to wind it with copper wire, w r ell cov- ered with cotton, or silk thread, and thoroughly insulated. The two poles can thus be brought very near to each other, and their combined magnetic power concentrated upon the same object at the same moment. The two arms must both le wound in the same direction, in order ihat their effect may coincide and produce but two poles, one at each extremity of the curved bar. As soon as a connection is formed with the bat- tery, the curved bar becomes a very power- ful magnet, with its north pole at the end where the electrical current enters, and the so'Jth pole, at the end where it issues, as shown in Fig. 196, and will raise a very heavy weight ; but as soon as the connection with the battery is broken, the magnetic power is destroyed, and the weight falls with a crash. Mag- nets have been con- structed in this form which would suspend Large Electro-Magnet. 2,000 Or 3,000 Ibs., and 405. What is the most effective form of the electro-magnet ? What effects have been produced by powerful magnets of this kind? CUliVCD ELECTRO-MAGNETS. 387 in some cases 10,000 Ibs. By making and then breaking tlie current circulating around such an electro-magnet, we can bring into play or annihilate at once this immense force. The iron bar below the poles is called the armature of the magnet, and the effect is very greatly increased if it also consists of an elec- tro-magnet, inverted, with poles opposite to those in the upper magnet, and magnetized by the same current. As soon as the connection is formed with the battery, these two electro-mag- nets rash togsther with great power, and with a current of mod- erate intensity, are capable of supporting a weight of several tons. It has also been found that the power is greatly increased, if the helix, instead of being made of a continuous wire, be formed of several wires of limited length, each having its own connection with the battery. An electro -magnet, constructed on this principle, can be made to lift more than a ton with a single cylinder battery of small size. The same principle is well illustrated by what is called the magic circle, repre- sented in Fig. 197. Two semi-circles are made Fig. 197. of a stout bar of soft iron, and well fitted together so as to form a circle, and include a small helix of wound wire, H, the two ends of which are to be connected with the poles of a small battery. When the connection is made, it will be difficult to pull the semi-circles apart, and a very consider- able weight may be raised; but the instant the connection is broken, the semi-circles fall apart of themselves. 406. The Magnetic Telegraph. Advantage is taken of this power to make and to unmake a magnet, by means of transmitting and breaking a current of electricity, in the construction of the magnetic Telegraph. This is the most important of the uses which have been made of galvanic electricity, and it deserves a minute description. Magic circle. The electric telegraph consists of three parts, viz. : 1st, the battery, or source of electric power ; 2d, the wire for the transmission of the current ; and 3d, the electro-magnetic instrument for making the signals. 1st. The battery. Any form of the galvanic battery may be employed ; but the most common form is Daniell's constant battery. Two batteries are required in order to establish telegraphic commu- Describe the magic circle. i05. What is the magnetic telegraph I "388 THE MAGNETIC TELEGRAPH. mcation in both directions between two places, one at each end of the line. 2d. The wire. There must be a wire extending be- tween the two places, in order to convey the current. This wire is connected with either pole of the battery, and is then carried upon posts, 15 or 20 feet in height, to the distant place. It is usually made of copper or iron, and is attached to the posts by some non-conducting substance. Sometimes it is insulated . by a suitable covering and buried in the ground, but it is prefer- able to carry it through the air, on account of the facility with which breaks may be discovered and repaired. When it reaches the distant place, it is connected with an electro-magnet, which then becomes part of the line, and on leaving the electro-mag- net, is conveyed to a large iron plate, buried in a moist spot in the ground, and there terminates. The electrical current, starting from the positive pole of the battery, traverses the wire to the distant place, circulates around the electro-magnet, then passes to the iron plate, and thence through the earth, back to the negative pole of the battery, and thus the circuit is made complete. It was at first supposed that a second wire was re- qu'red to bring the current back from the distant point, after it had passed through the electro-magnet, in order that a connec- tion might be formed with the opposite pole of the battery; but it was afterwards ascertained that the earth would answer as well a a second metallic wire, the great extent of conducting area which it exposes compensating for its feeble conducting power. In this manner a current is made to pass to any distant town, and to excite magnetism in an electro-magnet as soon as the wire is connected with either pole of the galvanic bat- tery ; and then when the connection with the battery is broken, this current can be made to cea>e, and the electro-magnet at the distant place de-magnetized. By this arrangement it is evident that a magnet can be made and unmade at any place, however distant, by simply making or breaking the connection between the wire and the battery. 3d. The instrument. Having now the means of creating a magnet at the point with which we wish to communicate, we have the means of producing motion, and giv- ing signals. Two instruments are required, one at each end of the line, for the purpose of receiving messages from both direc- tions, constructed on the following plan. Let an armature, con- sisting of a piece of soft iron, be suspended from one end of a What are the three essential parts of the telegraph ? How many batteries are required ? How many wires? How does the electrical current return from the distant |--ce '. i j ow many instruments are required i THE LINE. 389 lever, about one-tenth of an inch above the poles of an electro- magnet, placed firmly upon a pedestal, and with its two arms projecting upwards, in the manner of the letter U. It is obvi- ous that, when the current is circulating, this armature will be drawn to the magnet, and that the opposite end of the lever will be correspondingly elevated. If a steel point be at- tached to the upper side of the distant end of the lever, and a piece of paper be fastened firmly within one-tenth of an inch of it, a dot will be made upon the paper whenever the arma- ature is drawn down, anJ the steel point flies up. When the connection with the battery is broken by the operator, at the place from which the message is transmitted, the armature is released, and the distant end of the lever falls. As soon as the connection is formed again, the steel point again flies up and strikes the paper a second time. If the paper, instead of being stationary, is in motion, and carried steadily along upon a ro ler, the second dot will not coincide with the first, and if the steel point be pressed for some minutes against it, a long mark will be formed. Thus the operator at the other end of ihe line has the means of impressing dots, and broken or continuous lines, upon paper, at the place to which the message is to be sent, each one of which may be mads to represent a letter, and their com- binations, words and sentences. The return mes age requires a similar arrangement; first, there must be a battery; for the wire, the original wire may be employed, disconnected from the electro-magnet just employed, and connected with the positive pole of the battery at that end of the line; then there mu>t be an electro-magnet at the first place, which must be connected with the line on the one hand, and on the other, with an iron plate, buried in the ground. The operator to whom the original message was sent, must have the means of sending an electrical current back to the electro-magnet at the first place, and then es- tablishing a connection between it and the ground, so that it may return to him through the earth, and he replies by making and breaking the connection between the wire and the battery under his control. Thus the electrical current is made to pass to the first pla-.-e, there impress dots and lines on paper, in the manner already describee!, then descend to the iron-plate, and so return through the earth to the opposite pole of the second battery. This is an outline of the system known as Morse's telegraph. A sketch of it is given in Fig. 198; c, z, represents the bat- Explaiu the principle on which they are constructed. 390 THE INDICATOR. Fig. 198. Current passing tkrougk the Earth. tery ; n and jt>, the iron plates ; the arrows, the course of the current. There are other systems, but the principle is the same in all, the chief difference consisting in the arrangement of the electro-magnetic instrument. 407. morse's Blectro-Magnetic Indicator. In Fig. 1 99, is given an exact representation of the instrument used for mak- Fig. 199. Morsels Telegraphic Indicator. ing the signaK F E represents the electro-magnet which is made and unmade by forming and breaking the electrical connection at the opposite end of the telegraphic line. The connection between the instrument and the main wire is formed at the points Explain Fig. 198. 407- Describe Morse's indicator. THE MANIPULATOR. 391 a and b ; a is connected with the wire bringing the message, b with the iron plate buried in the ground. D is a piece of soft iron, which is drawn down upon the poles of the magnet when- ever the circuit is completed, and is raised again, whenever the current is broken, by the spring r attached to the opposite end of the lever A ; m, m, are two screws for regulating the play of this lever. At the extreme end of A, is a sharpened point which, when D is drawn down by the completion of the circuit, strikes against the band of paper upon the under side of the roller, H. This band of paper is continually moved forward by means of clock work carried by the weight, p. If the electrical circuit be formed, and then instantaneously broken by the ope- rator at the station from which the message is sent, the sharp point merely strikes the paper, and is immediately withdrawn by the spring, r, leaving only a dot behind it ; but if the circuit be maintained for an appreciable interval, the point, remaining longer in contact with the paper, leaves a line or mark behind it. Thus a long continuous, or broken line, may be produced, or a succession of dots ; and a set of different signals constructed, corresponding with the letters of the alphabet. B is a roller, around which the band of paper is wound. With this instru- ment it is necessary to translate the signals that are formed into the letters which they represent; but instruments of a much mare complicated character have been constructed, in which the message is recorded in printed letters. The instrument for ac- complishing this, was invented by Mr. House, and is a wonder- fully ingenious piece of mechanism. Mr. Bain has invented a telegraphic system, in whi^h no electro-magnet is used, but only the chemical influence of the current operating upon paper pre- pared with cyanide of potassium. 408. -JL'he Telegraphic manipulator and IVIorse's Alphabet. The instrument by which the message is transmitted to the distant place, is called the Manipulator, Jt consists of a wooden stand, Fig. 200, upon which is a metallic lever, , b, turning iipon a horizontal axis ; L is a wire communicating with the line ; B, a wire forming a connection with the local battery; and A, a wire connected with the iron plate in the ground. At #, there is a spring, by which the lever is raised and prevented from touching the metallic button under it ; and so long as this is the case, there is no connection between the local battery and the line, and consequently no flow of the current to the distant place ; but there is a connection with the local indicator, and, 408. Describe Morse's manipulator and alphabet. 392 MORSE'S ALPHABET. The Telegraphic Manipulator. Fi S- 20 - through it, with the line and the dis- tant battery on the 01 ;e hand, and with the iron plate, or the ground, on the other, eo that the in- strument, in this state, is always in a suitable condition for receiving a mes- sage. When it is desired to transmit a message, pressure is applied to the wooden knob, and the lever brought down upon the metallic button connected with the local battery, B, when a current immediately circulates through the point x, into the lever, then through m, into the line, and continues as long as pressure is applied upon the knob. Thus, by the depression and elevation of the knob, K, a succession of dots and broken lines may be impressed upon paper in the Indicator at the other end of the line, and it is only necessary to give these combina- tions a definite meaning. The alphabet adopted by Morse is represented in the following table. A - B -- - D E F Q. J K L M N - - - S T U - V W X H I 2 :- z -- - & In this manner words and sentences can be arranged, care being taken to leave a space between each letter. During the process of transmission a continual clicking proceeds from the armature of the Indicator where the message is received, and so clear and definite are these sounds to the practised ear, that the message can be interpreted by these sounds alone, without having recourse to the paper, and in many telegraph offices no other Indicator is employed than an electro-magnet, and movable armature, the pen and paper being dispensed with. The same manipulator, w T hen not used to transmit messages, is employed for their reception ; the current from the distant place eaters by THE RELAY. . 393 the wire, L, passes through m, to the metallic lever, thence through b, to the wire A, and by it is transmitted to the Indicator. 409. The Relay* In describing the Indicator, we have supposed that the current, after traversing the line, entered di- rectly into the electro-magnet, and worked the armature ; but wheii the current has proceeded a few miles, it can not act with sufficient force upon the electro-magnet to communicate the message. It can only be used to establish a communication between a fresh battery at the place where the message is sent, and the Indicator. The current then, instead of entering direct- ly into the Indicator, is carried into another instrument, called the Relay, Fig. 201, enters the electro-magnet, E, through the Fig. 201. The Telegraphic Relay. binding screw, L, and after traversing the coils, descends into the earth by the binding screw, T, and returns back to the battery from which it started. Each time that a current passes over the line, and traverses the electro-magnet, E, it at- tracts an armature, A, which is suspended from a horizontal axis, and is extended up into a vertical rod, p. Whenever the armature, A, is drawn towards the electro-magnet, it drives the lever, ;?, in the opposite direction, against a button, n ; as soon as p touches w, a powerful current from the positive pole of a fresh battery placed beneath the table, and not seen in the. figure, enters at r, passes up the pillar, m, to n, then down p, to t western extremity of America, and at no distant day will completely encircle the globe. 410. The Transmission of Messages. If there are inter- mediate stations, the telegraphic current, in passing from one 396 TELEGRAPHIC BATTERIES. extremity of the line to the other, circulates through the instru- ments of all the stations, and every message is repeated simul- taneously by every Sounder, even by those which are far in advance of the station to which the message is sent. When a message is to be transmitted from one end of the line to the other, or to an intermediate station, the operator first signals that station by sounding several times in rapid succession the first letter of its name, as s, for Springfield, if, for Boston, in order to call attention. This signal is repeated at every station down the whole line, to the most distant extremity, but it re- ceives no notice except at the place to which it is sent. The operator at this point responds, to show that he is in readiness, and the message is then transmitted. No message is ever sent, until the operator at the proper station has been summoned. The reply is transmitted by means of a Manipulator, as already described, and this reply is also repeated by every Sounder on the line, both behind' as well as in advance of the station from which it started, but receives no attention except from the oper- ator who has been summoned. In consequence of this repetition of messages in every instrument, it is easy to transmit news to many points on the same line simultaneously. The news from New York City for the morning newspapers in New England, is transmitted simultaneously to all, by one operator at New York. The first thing done, is to call up the operators at the different points, by striking the signals appropriate to each place in succession, and when it has been ascertained by a reply that each 'is at his post, the news is transmittt-d. If it be de- sired, however, the operator who is summoned at any station can prevent messages from going further, by breaking connec- tion with the line beyond him, and replying by his own battery and local ground connection. By a recent improvement the same wire can be used to transmit messages in opposite direc- tions, at the same moment. 411. Telegraphic Datteries. Several new batteries have been constructed within a few years, which are now occasionally employed for telegraphic purposes instead of the batteries already described. The most important are the sulphate of Mercury battery, Caillaud's battery, and the Sand battery. The sulphate of Mercury battery, Fig. 202, No. 1, is gener- ally arranged like Bunsen's battery, but the dimensions are less. In the outside cup, in place of water acidulated with 410 Explain the transmission of messages simultaneously to different stations. 411. Describe the new Telegraphic batteries : The Sulphate of Mercury battery. CAILLAUD'S BATTERY. 397 Tke Sulphate of Mercury Bailer y. Caillaud^s Battery. Tke Sand Battery. sulphuric acid, pure water is used or else water containing com- mon salt chloride of sodium in solution ; in the porous cup, in place of nitric acid, a solution of the sulphate of mercury is employed. This salt not being very soluble is mixed with three times its weight of water ; the water is then decanted and a pasty residue left: the zinc plates, z, and the carbon cylinders, c, having been put into their places, the porous cups are then filled with this residuum, and afterwards the decanted liq lid is poured in. The action of the battery is extremely s'mple: the water in the outer cell being decomposed, the oxy- gen unites with the zinc plate, the hydrogen penetrate^ into the po: o is cup, and ds-oxidises the oxide of mercury, setting free metallic mercury and sulphuric acid ; the former settles at the bot'om of the porous cup, the latter passes through it, and unites with the oxide of zinc in the outer cup to form sulphate of zinc. The mercury may be collected and used to prepare a fresh quantity of sulphate, equal in amount to that which has been decomposed. This battery is soon exhausted when used continuously, but it can operate during three or four months > c o as to furnish interrupted currents like those which are used for telegraphic communication. 412. Caillaud's Battery This battery dispenses with por- ous cups and secures the separation of the two liquids which are required, by the difference in their density, assisted by the action of the current. At the bottom of the outside cup, v, Fig. 202, 412. Describe Caillaud's battery. 398 THE EARTH FORMS No. 2, a copper plate c, is deposited, to which is soldered a copper wire, insulated by means of a covering of gutta-percha, i. On the top of this plate is placed a layer of crystals of sulphate of copper. The remainder of the vessel is then filled with pure water; a cylinder of zinc, z, is then introduced, and so placed as not to touch the sulphate of copper. Thus the lower part of the liquid becomes saturated with sulphate of copper, while the upper part remains pure, the two liquids being pre- vented from mingling by a difference in density, and also by the passage of the current. The theory of this battery is the same as that of Daniell, 344 : the water surrounding the zinc plate is decomposed, the oxygen unites with the zinc, the hydro- gen passes into the sulphate of copper solution, and de-oxi- dises the oxide of copper which it contains, setting free metallic copper and sulphuric acid : the former attaches ibelf to the cop- per plate, the latter moves towards the zinc plate and mvtes wi;h the oxide of zinc to form sulphate of zinc : the direction of the current is from z to c. This battery is extremely eco- nomical, and will furnish a steady current for several months : a little water must be added from time to time to replace that lost by evaporation. 413. The Sand Battery. In this battery, which is ar- ranged upon the same plan as the last, Sand is employed in order to render the separat'ori of the liquids more complete. The sulphate of copper broken into coarse rowder, is intro- duced first, forming a layer from a to 6, Fig. 202, No. 3 : above it is placed the copper plate c, with its insulated wire i : on the top of this, a layer of sand, from b to c: then the zinc plate, z, and the remainder is filled with pure water. Sometimes, the sulphate of copper in crystals is placed on the top of the copper plate, and the sand immediately above it. These new batteries, however, have not superseded the batteries of Daniell, or Grove, for ordinary telegraphic use. 414. The Earth as a part of the Telegraphic circuit. One of the most remarkable facts connected with the working of the telegraph, is the extreme facility with which the Earth conducts the electrical current. It had been shown by Wat i- on, in the last century, that a Leyden jar could be discharged through a circuit one-half of which consisted of moist earth, but cSteinhcil was the first to employ the earth to act the part of a conducting wire in a telegraphic circuit. While engaged 413. Describe the Sand battery. 414. What is said in regard to the earth as a part of the telegraphic circuit '! Who discovered this fact ? , A PART OF THE 399 in 1837, upon the railroad from Nuremburg to Furtli, in ex- periments with a view to realize a hint thrown out by Gau-s, that the two rails of a railway might be employed as conductors of the telegraphic current instead of wires, and finding it im- possible to obtain an insulation sufficiently perfect tor tho current to reach from one station to another, he was led to notice the great conducting power of the earth, and to conjec- ture that it might be. employed as a conductor in place of one of the telegraphic wires. His experiments were crowned with success, and he then introduced into telegraphy one of its greatest improvements, both in regard to economy from the sup- pression of one wire, and greatly increased facility in the con- struction of long lines. The two extremities of his telegraphic lines constructed at Munich in 1839, were attached to two copper plates, which were buried in the earth, and he attrib- uted the transmission of the current to the direct conduction of the earth. In 1841 it was proved, by Wheatstone and Coolte in Eng- land, that the earth may be employed to replace one-half the conducting wire, and be used for the return circuit ; indeed they found that the same battery would work to a much greater distance, with a circuit half wire and half ear h, than when al- together wire. It was noticed by Bain in 1841, that when a plate of copper was buried in moist earth, and connected by a wire passing through a galvanometer with a similar plate of zinc also buried in the earth at sone distance fro n it, that a cuivent of considerable intensity was generated by the ac-ion of the zinc on the moist earth ; and on increasing the size of the pla f es, not only were powerful electro-magnetic effects obtained, but also electro-type deposits, even when the plates were more than a mile apart. The battery thus formed continued to wo k for a great length of time. In 1844, Matteucci caused the current from a single Bun- sen's element to circulate through a copper wire 9,281 feet in length, and through a portion of moist earth of the same ex- tent, for the sake of comparison. It was found that the earth conducted so much better than the wire that its resistance must be regarded as nothing, and that the resistance of copper wire entering into the earth circuit, was less than that offered by the same wire when it entered alone into the circuit. It was ascerjained by Breguet, on the telegraph line between Paris How was it discovered? What did Bain discover? Matteucci? Why is the con- duction of the earth of great importance in telegraphy ? 17 400 TELEGRAPHIC CIRCUIT. i and Rouen, that when the current traversed a circuit half metal and half earth, the intensi:y was twice as great as when the circuit was metallic throughout that is, a chcuit 40 miles earth and 40 miles wire, presented no more resistance than a circuit of 40 miles wire, the earth in fact offering 110 resist- ance at all. This is a fact of the greatest importance, as it not only permits the economy of a one line wire, but a'so renders the cur- rent twice as strong as it would be if returned by a eecor.d metallic wire. Two explanations have been given of this non-resistance of the earth ; one, that as the conducting power increases in proportion to the area of a section of the conductor, the earth acting as a conductor with an infinite area, offers a smaller amount of resistance than the metallic part of the cir- cuit ; the other, that the earth acts as an immense reservoir which ab orbs all the positive electricity poured into it on the one side, and the negative on tha other. According to the first theory, between two stations very far apart, such as Washing- ton and St. Louis, there must be a process of polarization like that described in 333, Figs. 139, 140, and a series of decom- positions and recompositions of all the intervening molecules of water, with which the moist earth is charged, 365, Fig. 103 : and the positive electricity, introduced into the ground at Wash- ington, can only be neutralized by the negative electricity of the same battery, which has gone by wire to St. Louis, and thence back through the earth by a process of polarization and neu- tralization going on from molecule to molecule, of the interve- ning section of earth. According to the second theory, the earth, on account of its immense size, has an unlimited capacity for electricity, and by absorbing all the positive and negative electricity which is gen- erated by the battery, produces a flow of the electric current in the wire : or the earth may be regarded as an immense battery, producing electric currents that are passing in different direc- tions, with some one of which the galvanic current forms a connection, making it part of the telegraphic circuit : thus the comparatively feeble current which traverses the line, runs into and is absorbed by the mighty current of the subterraneous bat- tery below, and is hurried on with a greatly accelerated velocity. Objections may be raised in reference to both these theories, but the former is more in accordance with the principles pre- State the two theories by which it is explained. Which is preferred? THE VELOCITY OF THE TELEGRAPHIC CURRENT. 401 viously laid down, in regard to the necessity for the polarization of the entire circuit before the current can be transmitted. The fact that the resistance of the earth to the passage of the tele- graphic current is absolutely null, is certain, however difficult may be its explanation ; and in reference to its influence upon the moral and social welfare of men by dispensing with the necessity of a second return wire of the same length with the first, and thus greatly facilitating the rapid extension of the tel- graph over the whole earth, it is one of the most important discoveries of the age. 415. The velocity of the Telegraphic current. It has been ascertained by an ingenious apparatus devised by Wheat- stone, that the velocity of statical electricity discharged through a copper wire half a mile in length, is 288,000 miles in a sec- ond, being greater than the velocity of light in the ratio of 286 to 192. In regard to the velocity of voltaic electricity traversing a wire, there is some discrepancy in the results of experiments, but they agree in showing it to be very great. Thus, according to Prof. Walker of the U. S. Coast Survey, it is 18,780 miles per second. Mitchell, 28,524 " " " Fizcau and Gounelle, copper wire, .... 112,680 " " u " " " iron wire, 62,600 " " " Astronomers of Greenwich and Brussells, cop- j per wire, of London and Brussells Telegraph, 2,700 " " " . Astronomers of Greenwich and Edinburgh, copper wire, of London and Edinburgh Tel- egraph, 7,600 " " " 1 Gould, 15,890 " " " From the above table it would appear that the velocity of vol- taic electricity is very much less than that of statical. It is probably not more than 20,000 or less than 12,000 miles per second. Taking Walker's estimate of 18,780 miles per second, it would require 1^ seconds for the galvanic current to traverse a wire extending round the earth. The transmission of tele- graphic signals must therefore be practically instantaneous. 416. The Sub-marine Telegraph. In the sub-marine tele- graph, copper wires, coated with gutta-percha, are wound around a central rope of hemp, in such a manner as to form a compound rope, containing several strands of conducting wire ; the whole 415 What is the velocity of statical electricity ? Of galvanic electricity ? Giv the various results. What is th* rate of transmission of the telegraphic current? IIo\v much time is required for its circulation around the globe? 416. Describe the sub- mariue telegraph. 402 THE SUB-MARINE TELEGRAPH. is protected by a flexible metallic covering of woven wire, and then this is covered with an exterior covering of gutta-percha, or tarred hemp. The metallic cable is coiled in the hold of a steamer, and one end having been made fast to the shore, and connected with a land telegraph, the rope is gradually paid out over the ship's stern, as she moves steadily forward, and from its weight sinks to the bottom of the sea. When the opposite shore is reached, the end of the cable is landed and connected with a land telegraph. In working a telegraphic line consisting of wires covered with gutta-percha, and sunk beneath a body of water, it has been observed that when the cable is connected with the battery, the signal is not instantaneously transmitted to the distant extremity ; and on the other hand, if the connection with the battery be broken, there is not an instantaneous cessa- tion of electrical action at the distant extremity. There is, in short, a retardation, and subsequent prolongation of the electrical current. This is owing to the action of the current upon the gutta-percha insulator. The insulated wire constitutes, in fact, a Ley den jar, of which the wire forms the inside surface, the gutta-percha constitutes the containing vessel ; the external iron wire, or the water of the ocean, forms the outside metallic covering. The time lost at fir.-t, is that which is consumed in giving the gutta-percha its charge ; being a non-conductor, its particles are all polarized in the manner represented in Figs. 119, 124, by the highly electrified wire. If the wire is carrying a current ^positive electricity, the gutta-percha becomes highly charged with a proportionate amount of negative electricity, and as opposite electricities attract each other, this induced negative electricity reacts upon the positive electricity with which the wire is charged, exerts an attractive influence upon it, and tends to hold it fast, and to check the flow of the current in the wire. If the wire is carrying a current of negative electricity, the effect is reversed, the gutta-percha receives by induction a charge of positive electricity, and an equal retardation is pro- duced in the flow of the current through the wire. On the other hand, when the connection with the battery is broken, and the current of electricity carried by the wire is stopped, there is a gradual cessation of the polarized state in the gutta-percha, and a steady decline in the tension of the induced charge which it had received, and this allows of the gradual escape of the electricity, which it had held back, during some seconds after the Describe the retardation and prolongation of the electrical current. Show how the Insulated wire constitutes a Leyden jar. THE ATLANTIC TELEGRAPH CABLE. 403 Fig. 203. connection with the battery has ceased. When wires, covered with gutta-percha, are suspended in the air, no such polariza- tion takes place, on account of the non-conducting power of the air, which do. j s not allow of the escape of the repelled ele> triclty, and the wire is therefore like a Leyden jar, who^e outside surface is not connected with the earth, 317. 417. The Atlantic Telegraph Cable. The Atlantic Tele- graph Cable, which was successfully laid in 1866, is constructed of a core of 7 copper wires imbedded in gutta-percha, and protected by a twisted strand of ten steel wires covered with tarred hemp, Fig. 203. The total diameter of the cable does not exceed l^j inches. Three cups only of the weakest possible form of the galvanic battery are used, each consisting of a plate of copper, at the bottom of a glass jar about 8 inches in depth, filled in with saw dust dampened with pure water without the u-e of "any aciJ, and a piece of zinc placed upon the top of it, Fig. 204. An insulated wire is at- tached to each copper plate leading to the zinc plate in the Fig- 204. Sftion nf th' Atlantic Tdegrapk Cattle. Tke Atlantic Telegraph Battery. adjoining jar. A few pieces of sulphate of copper are dropped upon the copper plate previous to covering it with saw du>t. No Indicator is employed like that described in 407, but in- stead of it an extremely simple instrument, called Thomson's Reflecting Galvanometer, Fig. 205. 417. Describe the Atlantic cable, and the battery used to work it. 404 THE SIGNAL INSTRUMENT. Fig. 205. Thomson's Effecting Galvanometer, in section. It consists of a coil of wound wire, seen in section, at c, having a very small magnet, m, suspended with- in it by a single filament of silk ; on the front of this magnet is fastened a small mirror, n, and the magnet and mirror are made to as- sume a fixed position, at right angles to the axis of the coil by the permanent liorse-shoe magnet, s N. A D, is a screen, at a dis- tance of about 26 inches from the magnet, having a vertical slit, cut directly opposite to the mirror, n, and behind this slit is placed a lamp, B. The screen is graduated on each side of the slit, each divis- ion being about 4^1 h of an inch in length : L is a lens by which the light proceed- ing from the lamp is con- centrated upon the mirror. The extremities of the coil, C, are connected with the telegraphic wire in such a manner that the current may at pleasure be made to circulate through it. An electrical current, passing through the coil, however sligi.t, tends to counteract the attractive influence of the fixed magnet, s N, and to turn the magnet, m, into a position at right angles to its former po;-ition, and parallel to the axis of the coil. As long as no tele- graphic current passes THOMSON'S REFLECTING GALVANOMETER. 405 through the coil, the magnet, m, remains undisturbed in its fixed portion, and the light proceeding from the lamp, B, passing through the vertical slit, and falling upon the mirror, 71, is reflected back upon the same line and returns through the slit to the lamp, but the instant the current passes, the mag- net is made to deviate from its fixed position either to the right or to the left, and a spot of light is reflected to the right or left of the slit, and made to fall upon the graduated scale, A D. If the positive current turn it to the right, and throw the reflected spot of light to the right of the vertical slit, a neg- ative current will turn it to the left, and throw the reflected spot to the left of the same slit. The telegraphic operator has the power of transmitting a positive or negative current at pleasure, by means of the key, M, in Fig. 207 : when it is moved so as to touch jt>, a positive current is transmitted ; when it is moved so as to touch n, a negative current is trans- mitted. Thus the spot of reflected light is easily thrown either to the right or the left on the graduated scale, A D. When thrown to the right, a dot is indicated ; when thrown to the left, a dash ; and fro n these tha characters of Morse's alphabet, 408 are readily produced. By this very simple apparatus, the longest messages can be sent from one side of the Atlantic to the other. The observer who receives the message sits upon the side of s N opposite to B, and with the instrument, is placed in a dark room. 418. Thomson's Reflecting- Galvanometer. The actual form of the Reflecting Galvanometer employed may be seen in Fig. 206 : w represents a cylindrical box containing the coil of wire having the magnet and mirror suspended in it by a few fibres of unspun silk ; in the front of the box at the opening of the coil, is placed a small lens, /: the coil with its con- necting wires is mounted upon a stand, and provided with leveling screws. Upon a perpendicular rod mounted upon the top of this box, slides the horse-shoe magnet, m, by which, when brought down upon the sides of the box, the operator is enabled to give a fixed position to the internal magnet carrying the mirror. At R, is seen the screen, bearing the graduated scale ; at L, the lamp, placed behind the screen, and at s, the vertical slit, through which the light passes to the lens, Z, by which it is concentrated upon the mirror, and from this reflected upon the scale, R. As a very slight angular deviation of the magnet causes the spot of light to traverse the whole scale, this Describe the Signal instrument, Fig. 205. How is the passage of the current mani- fested . How does the reflected spot of light communicate intelligence? Why does the observer sit in a dark room ? 418. Describe the actual form of the Signal instrument. 496 THE ARRANGEMENT OF THE CABLE. instrument becomes an extremely delicate indicator of the pas- sage of the current through the cable. The observer sits behind the box, w, in a darkened room. The coil, mirror and magnet, are seen in section, separately on the right of the engraving. Fig. 206. The Atlantic Telegraph Signal Instrument. 9:19. The actual arrangement of the Cable. The actual arrangement of the battery and cable is represented in Fig. 207 : B and B', represent the two batteries, and E, the plate buried in the ground on one side of the ocean ; M, is the key for sending at pleasure either a positive or negative cur- rent ; A, the point at which the cable enters the sea ; G, the signal galvanometer; p, the p T ate buried in the earth on the other side of the ocean. The current circulates from one pole of the battery through A to G, thence to the plate F, and from this returning through the or'ean to the plate E, finally reaches the opposite pole of the battery to that from which it started. To use the cab^e advantageously, a uniform current of positive or negative electricity must not be employed, but the current should be often reversed; this is accomplished, in the instrument above described, by the constant alterations re- quired to produce the dots and dashes, as already described. 419. Describe the actual arrangement of the Cable. THE RATE OF TRANSMISSION. 407 Fig. 207 Transmission of the current across the Ocean. 420. The rate of trans- mission. The signal is transmitted instantly, but a slight delay of perhaps gthsofa second is expe- rienced in freeing the ca- ble. The rate of transmis- sion is fifteen words or seventy-five letters per minute, but twenty words can be sent quite easily. There is no doubt that with the various land lines free from other du- ty, a despatch of twenty words could readily be transmitted from London to New York, or vice versa, in the time requir- ed to write it over four or five times ; or in other words, it is possible to send it the entire distance in five minutes, every thing being in readiness for it. The difference of time being greatly in fa- vor of New York, des- patches often reach New York dated at a later hour than that at which they arrive. The news pub- lished in the New York afternoon newspapers, leaves London often at 3 p. M. of the same day. On one occasion a des- patch was received at New York at about 1 1 .30 p. M., dated London the following day. On an- other occasion a despatch from Rome reached New 408 HISTORY OF THE ATLANTIC CABLE. York at 8 A. M. on the day of its date, was placed in a "Western city at 8 A. M., and the reply which passed New York eastward about 1 1 .30 A. M., doubtless reached Rome in the evening of the same day. On one occasion a despatch was sent from London to Washington in nine minutes and thirty seconds, and was received in Washington four hours fifty-eight minutes and thirty seconds in advance of the hour of its leaving London. On the morning of Feb. 1st, 1868, the wires of the Western Union Telegraph Company from San Francisco to Plaister Cove, Cape Breton, and the wires of the New York, Newfoundland, and London Telegraph Company from Plaister Cove to Heart's Content, were connected, and a brisk conversation commenced between these two continental extremes. Compliments were then exchanged betwen San Francisco and Valentia, Ireland, when the latter announced that a message was just then being received from London direct. This was said at 7.20 A. M., Valentia time, Feb. 1 : at 7.31 A. M., Valentia time, the London message was started from Valentia for San Francisco ; passed through New York at 2.35 A. M., New York time ; was re- ceived in San Francisco at 11.21 P. M.,Jan. 31, San Francisco time, and was at once acknowledged the whole process oc- cupying two minutes actual time, and the distance traversed about 14,000 miles! Immediately after the transmission of the message referred to, the operator at San Francisco sent an eighty-word message to Heart's Content in three minutes, which the operator at Heart's Content repeated back in two minutes and fifty seconds : distance about 5,000 miles ! Notwithstand- ing the great length of ihe Cable no supplemental battery is required, because the whole force of the current is transmitted, none being lost as in the case of the Land Telegraph through imperfect insulation. 421. History of the Atlantic Telegraph. The construc- tion of the Atlantic Telegraph is considered one of the most remarkable scientific achievements of the present Century. The first and second attempts at laying the cable in 1857 and 1858 were unsuccessful. The third attempt somewhat later in the year 1858 succeeded, and telegraphic communi ation across the Atlantic was maintained from Aug. 6th to Sept. 1st, two hundred and seventy-one messages having been transmitted from Newfoundland to Valentia, and one hundred and twerity- 420. State the rate of transmission. Mention instances of the rapid transmission of despatches. Explain how a message from London may be received at ^ew York the day before it is sent. 421. Give the history of the Atlantic Cable. MOTIOX PRODUCED 409 nine from Va'entia to Newfoundland. On August 31st two important messages were sent to the British government from Newfoundland, but the next day communication ceased, and no efforts to reestablish it proved of any avail. In 1865 the enterprise was renewed with an improved cable, which was successfully laid by the Great Eastern about half way across the Atlantic, when it parted, and all efforts at recovery failed. In 1866 the undertaking was renewed with a new cable, which was successfully landed in Newfoundland July 27th. The ships then returned to mid-ocean tor the purpose of finding and raising the lost cable of the previous year. It was found with- out difficulty, and after many unsuccessful attempts, was fin d y raised, spliced to the remaining portion, and the whole Ian led at Newfoundland, Sept. 7th. The successful laying of these cables is due to Mr. C. W. Field. 422. Application of El2ctro-T!YIa Describe Pugc'd axial eugiue. 412 THE ELECTRO-MOTOR OF M. JACOBY. chine, a grinding mill for example, which it is desired to move. The machine employed in the workshop of M. Froment is of about one-horse power. 424. The Electro-lKotor of XVX. Jacoby. Electro-magnetic engines of much greater power have been constructed. In 1838, M. Jacoby, at St. Petersburg, built an electro- magnetic eng'ne of sufficient power to propel a boat containing twelve persons, upon the river Neva. The vessel was a ten-oared shallop, pro- vided with paddle-wheels, to which motion was given by the electro-magnetic engine. The boat was 28 feet long, 7^ wide, and drew 2f feet of water. During a vo\ age which lasted sev- eral days the Vessel went at the rate of four miles an hour. In 1839, a second experiment was tried in the same boat, the machine being worked by a Grove's battery of 64 platinum plates, each having 36 square inches of surface. The boat, with a party of fourteen persons on board, went against the stream at the rate of three miles an hour. 425. Electro- Magnetic Locomotives. About 1840, an electro-magnetic railroad engine was constructed by Mr. David- son, in Scotland, and tried by the inventor on the Edinbuigh and Glasgow railroad; it weighed, with its carriages, batteries, &c., five tons, but when put in motion it traveled only four m'les an hour, exerting a power less than that of a single man. The arrangement of this engine was not unlike that exhibited in the machine, Fig. 208, the chief difference being that two e'ectro- magnets were employed instead of one, and arranged in such a manner as to operate directly upon the shaft of the engine, the magnetism of the electro-magnets being perpetually induced and destroyed at the proper moment by making and breaking connection with the battery. 426. Page's Electro-Magnetic Locomotive. Some very efficient electro-motors have been constructed by our country- man, Dr. Page. With an electro-magnetic locomotive provided with two of these machines, rated at four-horee power each, actuated by a Grove's battery of one hundred pairs, a speed at the rate of nineteen miles an hour upon a level grade was at- tained : the car weighed eleven tons, and carried fourteen passen- gers. The engine employed was the axial engine. In all other engines the motion is produced by electro-mr.gnets of Foil iron, which are alternately magnetized and de-magnetized, as in Fig. 424. Describe the Electro-motor of M. Jacoby. 425. Describe Davidson's Electro- maguetic Locomotive. 426. Describe Page's Electro-magnetic Locomotive. PAGE'S ELECTRO-MAGNETIC LOCOMOTIVE. 413 208, and in Froment's electro-motor, Fig. 209. In this machine the electro-magnets are dispensed with, and a long hollow helix is employed, consisting of several distinct helices, placed o:ie abave another, so as to make a hollow tube, each having inde- pendent connections with the battery, insulated from each other, and arranged in such a way that each helix can be mag- netized and de-magnetized in succession. It is well known that a helix of wound wire itself becomes magnetic, and possesses as much attractive power as the iron armature placed witlrn it, Fig. 184, p. 363. If such a helix, mounted in a vertical position in such a way that an iron rod can be introduced into it from below, be connected with a battery, the iron rol wi.l be at once drawn up into it and be sustained oscillating in its axis, even though it may weigh many pounds. On one occasion, by means of a huge helix, a weight of 2,0 >0 Ibs. was raised five inches from the floor, and caused to vibrate for an inch up and down by the pressure of the finger. The battery used was fifty pairs of Grove's, with platinum plates twelve inches square, ten inches immersed. This is called the axial force of magnetism. If the iron rod be suspended over the opening of such a helix, as a b, in Fig. 210, instea 1 of under, it will be drawn down with equal i. 210. f . , iorce as soon as the wires, />, n, are conn -cted with the battery. In the interior of this compound helix a powerful steel magnet is suspended with its upper end upon a level with the top of the helix, and fastened to a connecting rod attached to a crank and axle. As soon as the helix opposite its lower end is magnetized, a powerful attraction is exerted The. axmi electro- upon the magnet, tending to draw it down- wards: as it descends, it de-magnetizes, by means of a proper break-piece, every helix that it passes an I leaves behind it, while it magnetizes in succession every helix in advance of it. When it reaches the bottom of the compound helix the process is reversed, every helix above it is succes- sively magnetized, while every helix that it passes is immedi- ately de -magnetized. Thus the magnet is made to rise again to the upper portion of the compound helix, and a reciprocating motion is produced which is imparted to the crank and axle. An axial engine of this description was exhibited at the Smith- W'vtt 5s the n.r>a> force of magnetism? What extraordinary effects are produced by this force ? Describe rage's axial eugiue. 414 THE COST OF ELECTRO-MAGNETIC sonian Institute of four or five horse-power, the battery of which was contained within the space of three cubic feet ; it wa> a reciprocating engine of two feet stroke, and the whole, including the battery, weighed about one ton. 427. Stewart's Electro-HSotor. Recently an electro-motor has been constructed by Mr. Stewart, in New York, in which a central axis about tiiree feet in length, is surrounded by a series of electro-magnets so placed that magnetic action is maintained continually, and without intermission. The magnets are only magnetized twice in one revolution, instead of many times as in most oUier motors that have been constructed ; it ij claimed that much greater power is obtained, arid at far less expense than any other machine that has been invented. The shaft makes five hundred revo utions per minute, with a battery of forty cells, producing one-tenth of one-horse power, and at an expense of about twenty-nine cents per cell for forty-eight hours. 423. Tho expanse of Electro-mag-netisin compared with Ctoam. As yet electro-magnetic engines have not been intro- duced to any extent, because the expense of the zinc and acids which they consume is far greater than that of the coal required to produce an equal force by means of steam. Careful experi- ments have shown that the economic difference between a steam and an electro-magnetic engine, is as follows : A grain of coal burned under the boiler of a Cornish engine, lifted 143 Ibs. 1 foot high. A grain of zinc consumed in a battery to move an electro-magnetic engine, lifted ...... 80 Ibs. 1 foot high. The cost of coal is, per cwt., 9c/. The cost of zinc is, per cwt., 216c?. There is considerable diversity of opinion as to the amount of zinc consumed in the production of one-horse power. Page computes the consumption of zinc in his engine at 3 Ibs. of zinc per day, for one-horse power. Joule calculates the con- consumption under the most favorable circumstances, at 45 Ibs. per day, for one-horse power in Grove's battery, and in Dan- iell's battery at 75 Ibs. There are also other disadvantages : the combustion of metals witli a three or four-horse power engine, is very rapid at all the points where the current is broken in de- magnetizing the electro-magnets. The power is also appplied at a great mechanical disadvantage, and the conversion of elec- 427 Describe Stewart's electro-motor. 428- State the comparative expense of eleetro- magnetism and steam. POWER COMPARED WITH STEAM. 415 tro-magnetism into mechanical force is attended with mu2h more loss than the conversion of heat into motion in the steam- engine. This is due in part to the very great reduction in the power of the magnet the instant the armature is separated from it ; and the larger the magnets and engines, the greater the loss of power. These objections are less applicab'e to Pace's en- gine, constructed on the axial principle, than any other. The cost per day, however, is not necessarily conclusive against these engines ; notwithstanding the great expense they inny, under certain circumstances, be usefully applied, especially in trades and occupations of small capital, where the abso- lute amount of mechanical power is a matter of less conse- quence than the facility of producing it instantaneously and at will : this would be the case even though the power should co t twenty times as much as the sama a nount furnished by a Cornish steam engine. To this must be added th ' important consideration of perfect safety and the entire freedom from the danger of explosion, 429. Electro-magnetic Clocks, Electro-magnets are often used as a motive power in clocks. The oscillation of the pendu- lum establishes and breaks the connection between an electro- magnet and a battery, in such a way as to give to the pendulum by the raising and dropping of an armature, sufficient impulse to maintain its motion. This interrupted connection may be com- municated by a wire to all the clocks in a large city, and cause them to move at exactly the same rate, and thus one central clock may become the motor and regulator of an unlimited number of time-pieces. Such clocks, however, steadily deterio- rate in consequence of the rapid combustion which takes plac^ at the points where contact with the battery is made and broken ; and for this reason a clock of ordinary construction moved by a weight and spring, is employed to furnish the standard time, and its pendulum as it oscillates is used to reg- ulate the current which turns the hands upon an indefinite number of electrical dials. Fig. 211 represents a dial of th ; s description, and Fig. 212, the mechanism by which its hands are turned. An electro-magnet, B, is used to attract an arma- ture of soft iron, p, turning on a pivot, a. This armature trans^ mits its motion to a lever, s, which by means of a ratchet turns the wheel A. This, by the pinion D, turns the wheel c, and 4?9 How miy a pendulum he made to oscillate by electro -m;i:netisni ? How may on4 clock bo made to indicate time on many dials in different places 7 Describe Ftsi. 2U ami 213 416 ELECTRO-MAGNETIC CLOCKS. Fig. 211. Fig. 212. Tlie Electro-magnetic Clock. this, by a series of wheels and pinions, moves the hands. The regular motion of the hands depends upon the regularity of the oscillations of the armature P, and this regularity is maintained by making and breaking the connection between the electro-mag- net B, and the battery, by the movement of the pendulum of the standard clock mentioned above. In this manner, all the clocks in a city, in a large hotel, or on the line of a railroad, may be made to indicate exactly the same time, for the electrical cur- icnt, travelling at the rate of 18,780 miles in a second, takes but an inappreciable time to traverse the who!e line. Mr. Bain has invented an electrical clock which is driven by the current derived from an earth-battery, consisting of one zinc and one carbon plate, imbedded in the ground, about four feet apart and three feet deep. 414, p. 385. The exact time when the sun or a star crosses the meridian at one observatory, can be telegraphed instantaneously to others, and to distant places: and it is thus that the exact time of noon is flashed from a central observatory to many distant points. Time at Hartford is telegraphed from New York, and this from the Dudley Observatory at Albany. Other applications have been made of electro-magnetism to the bells of hotels and hou.-es, and other minor conveniences of house-keeping. How can time be transmitted from one place to another ? THE ELECTRIC 417 430. The Slcctric Fire-Alarm. One of the most interesting and useful applications of galvanic electricity is to the construc- tion of the fire-alarm of cities. A central office is established, where a battery is placed which is always in aciion. From this a wire proceeds to every part of the town, and is carried at suit- able points, into the interior of iron boxes fixed at the corners of the streets : after entering each box the wire again emerges, and is carried to the next box, and so on in succession through them all, and is finally returned to the opposite pole of the battery from which it started. Thus an electrical current is constantly kept in circulation through every part of the entire city circuit. The internal arrangement of the box is repre- sented in Fig. 213. The current enters at o, by means of an The Electric Fire-Alarm, 430. Describe the Electric Fire-Alarm. Describe the arrangement of the wire. How IB tue cur.i'ut broken.' 418 FIRE insulated wire, taking the course indicated by the arrow?, de- scending in the space between the outer and inner boxes, as far as n, and then ascending and passing into the interior circular box until it reaches B : B is a lever of wood, having its upper surface covered by a thin strip of metal, which by means of a s;>r,ng is firm'y pressed aga'nst the brass wheel w. By the side of the lever B, is a second lever which is con ealed in the Fig., constructed of wood, of the same dimensions, and having its upper surface covered also with a thin metallic strip, which is in Ike manner pressed firmly upon the wheel w, by means of a spring. Although these levers are placed side by side, there is no direct metallic communication between them, except by means of the wheel w. The current, when it reaches the first lever, B, descends upon the brass Ftrip which covers its upper surface, to w, through which it passes to the second lever, behind B, and ascends by the brass strip which covers it, to the upper end, whence it pusses by the wire as indicated by the arrow, to the electro-magnet E. After circulating through both arms of the electro-magnet, it emerges and parses by the wire in front of the bell G, to the lower part of "the box, and thernce by the wire p, ascends in the space between the outer and the inner box to the po^nt o, where it again enters the iron tube through win -h it ha 1 descended, and pa-ses on to the nc xt adjoining box. It will be observed that so long as both levers, B, rest upon the wheel w, the electric current circulates uninter- ruptedly through the apparatus : and that when one or both the levers cease to press upon the wheel w, the current craves to circulate. When a lire occurs, the box must be opened and the lever, L, pushed down as for it can be made to go. This movement winds up a spring and sets in motion a train of wheels by which motion is communicated to the wheel w. This wheel is not continuous, but is broken by notches in its circumfer- ence As each notch comes successively beneath the levers B, their connection with the wheel w, is broken, and the current c -ases to flow: this immediately de-magnetizes the electro- magnet r, and allows its armature A, to drop : at the same instant the current cea?es to circulate through the entire city CTCuif, and by releasing an armature attached to an electro- magnet in a central tower, sets in motion a train of machinery by wlii. h a heavy blow is struck once by a powerful hammer upon the Fire Bell, and an alarm sounded. As the wheel w, What must be done when an alarm is to be sounded 1 ALARM. 419 revolves, and each notch passes on, the communication between the levers B, and the wheel w, is re-established, the entire city c'rcuit is again rendered complete, the armature of the electro- magnet is aga^n drawn up, and the machinery in the central tower is stopped, one blow only having been struck upon the bell. If, however, there be more than one notch in the wheel w, as it revolves the process is presently repeated, and a second blow is given upon the bell. These notches may be cut quite near each other, at regular intervals, or far apart and at unequal distances: thus many combinations may be effected, by which a variety of blows may be struck upon the bell, characteristic of each box, and determining the locality of the fire. Each box is distinguished by a number, and the notches are cut i;i such a manner as to strike this number upon the bell. Thu -, if two notches be cut quite close together, and then, at some dis- tance from them, four other notches at equal distances from each other, the effect will be to strike two strokes in rapid suc- cession, and then, after a brief interval, four others, denoting the number 24, and indicating that box 24 is the one neare4 tti3 fire. By pulling the lever L, down once, the machinery is wound up just enough to make the wheel \v, revolve five times, and thus the number 2 4, in the above case, will be repeated five time?. With every completion of the circuit, the armature of the electro-magnet in each box is drawn violently back to the mag- net, and a stroke given upo'i the bell G. The alarm is there- fore repeated in every iron box in the city, and may be made to indicate the locality of the fire in every engine-hojse. The box is kept securely locked, and the lever L, is moved by means of a projecting pin, L, upon the inside of the open door, repre -en f ed in the Fig. This pin extends through the door, and may be moved upon the opposite side while the door is closed : s s, are springs for the purpose of restoring the pin L, to its former po ition after being once thrust down. The whole box is closed by an external do:>r not represented in the Fig., the key of which is kept in ?ome neighboring house. In some case?, the alarm is first telegraphed to a central office, and from that transmitted to a number of Fire-bells distributed over the city. The advantage of making use of a circuit which is con- stantly closed, instead of bringing the battery into use only at the moment when the alarm is to be sounded, is, that it furnishes evidence of being constantly in working order, and makes the How is the number of tae box struck upon the bell f 422" IN ELECTRO-MAGNETISM. with the same amount of galvanic force, was increased several times, and it was found that a current transmitted through a long wire could be used to create a powerful electro-magnet at the distance of many miles, and make signals by striking a bell, especially if a battery of intensity, 341, con.-isting of ninny cells, was employed. This discovery made the (on.-truction of an electro-magnetic telegraph, which had been tried without success in EngUmd in 1825, a possibility, and served as the foundation for Morse's electro-magnetic instrument. Prof. Henry still further increased the power of the electro-magnet by using a number of separate coils, having independent connection with the battery, on the same horse-shoe, in place of one long single coil. In this manner the powerful electro-magnets capable of sustaining from five to ten thousand pounds were made, which have since been u ed in the construction of electro-motors. He also exhibited the first mechanical motion ever produced by magnetic attraction and repulsion, by means of a vibrating beam placed horizontally over two upright magnets : a fly-wheel was subsequently attached to this, and afterwards a rotatory motion given. An account of this instrument is contained in Silliman's Journal for 1831. Finally, the constant battery of Prof. Daniell was invented in 183G ; the possibility of using the earth as a part of the tele- graphic circuit, was discovered by Stcinhcil in 1837 ; and in the same year these principles were applied by our countryman, Prof. Morse, to the construction of the electro-magnetic telegraph. About the same time, Wheatsfone and Cooke's needle telegraph was introduced in England; Daniell's and Grove's batteries were perfected in 1843; and the first telegraph line in the U. S. A. erected between Baltimore and Washington in 1844. THE SECONDARY CURRENT 423 , IV. Galvanic Induced Electricity. 433. Volta-STestric Induction. An induced secondary electrical current produced by establishing- and breaking- the primary current of a Galvanic Dattsry. We have seen tlmt the frictional electricity of the machine induces electricity in all surrounding bodies, 310. The electricity of the battery acts in a similar manner, but only at the instant when the current begins, and at the instant when it ceases, to flow : during its continu- ous flow, no inductive influence whatever is exerted by it. This fact was discovered by Mr. Faraday, in 1831. He found that a wire transmitting a powerful current, induces a momentary current in a second wire parallel to the first, the two extremi- ties of which are brought together, and united so a; to form a closed circuit, whenever the connection of the original wire with the battery is made, or is broken. This he called Volta- Electric Induction. The effect is much increased, if instead of employ- in;; simple parallel wires, the wires of the two currents are coiled into two helices and arranged one within the other. The wire which conveys the primary current, or the primary coil, is placed in the axis of the coil for the secondary current, and the extremities of the secondary coil are joined together so a< to form a closed or continuous circuit. A galvanometer is connected with the extremities of the secondary co'l, in such a manner as to form a part of the closed circuit, for the purpose of demonstrating the actual passage of the current. The pro- duction of a secondary current under these circumstances, may be shown by the apparatus repre'sented in Fig. 214. Let r Volta Electric Induction. -. ... . .... ..Jlv on al! other' nor it ? Whnt is the eff.-c t of a wire e.-irr.injr a current upon n c'o e 1 i a allel wire?' TT " " " M " J <""/- .. i,,n,ooea^ Wluit is the effect of fin electrified ho ' e 1 i a ire e.-irr.injr . a current upon n f'o e 1 i a ;iHel wire? Ho.v c.-m this effect >e increased? ' ' > discover..; 1 t',ie;.-fa,ct.-i? Wait 11.1111 d.d iie.ji.'e to t.iis i.idactive action? ib 424 INDUCED BY THE BATTERY. > represent the inner primary helix, composed of a short piece of stout wire carefully wound with silk or cotton and varn'shed with gum-lac, so as to be thoroughly insulated, and having its two extremities connected with the binding cups d and c, through which a connection is established with the battery. Let s, represent the outer secondary helix, composed of a great length of very fine copper wire, also carefully insulated, and entirely separated from the primary helix, and having its ex- tremities connected with the binding cups a and b, through which a connection is established with the galvanometer o, thus forming a closed circuit, of which the galvanometer is a part. The connection of the primary helix with the battery is made or broken at pleasure by connecting or disconnecting the bat- tery wire, by means of the hand, with the binding cup c. It is found that the moment the connection is completed with the battery, and the galvanic current begins to circulate through the inner primary coil P, a secondary current of positive elec- tricity instantly circulates in an opposite direction throrgh the outer coil, shown by the violent oscillations of the needle of the galvanometer. This pecondary current continues only for a moment and almost immediately cea es. If the connection of the primary coil with the battery be kept up, the flow of the induced secondary current ceases, as is shown by the needle of the galvanometer returning to its position of rest. Again, the instant that the connection of the primary col r, with the bat- tery is broken by removing the battery wire from the binding cup c, arid the primary current cea?es to flow through P, a mo- mentary secondary current of positive electricity, flowing in the same direction with the primary current, circulates throughout the entire coil, shown by the powerful impulse which it imparts to the needle of the galvanometer. These currents are only momentary, but are characterized by great power and intensity. Though the current of positive electricity is only spoken of, ac- cord ' ny to the principle laid down, 033, p. 309, it must be under- stood, that a momentary current of secondary negative electricity is also produced at the same time, flowing in the opposite direc- tion to that of the secondary positive: when contact wi;h the battery is completed, it circulates in the Fame direction with the primary current : when contact with the battery is broken, it circulates in the opposite direction. The secondary electric current thus induced is not derived from the battery, nor from I)f><iat Is the effect of lengtheuing the secondary coil ? 434. Give the history of Mr. i'araday's discovery. 426 THE DISCOVERY. coppers, and well charged. When the contact was made, there was a sudden and very slight effect at the galvanometer, and there was also a slight similar effect when the contact with the Lattery was broken. But whilst the voltaic current was cont : n- tiing to pass through the one helix, no gulvanometrical appear- ances nur any effect like induction upon the other helix could La perceived, although the active power of the battery was p/oved to be great by its heating its own helix, and by the bril- liancy of the discharge when made through charcoal. Repeti- tion of the experiments with a battery of one hundred and twen y pairs of plates, produced no other effects : lut it was ascena ried, loth at this and the former time, that the slight deflection of the needle occurring at the momeitt of ccmpletii g the connection, was always in one direction, and that the equal y slig'it deflection produced when the contact was broken, was in the other direction ; and also that there effects occurred when the first helices were used. The results which I had by this time obtained with magnets led me to believe that the lattery current through one wire did in reality induce a similar current through the other wire, but that it continued for an instant cnly, and partook more of the nature of an electrical wave parsed thro igh from the shock of a common Leyden jar, than of the current from a voliaic battery, and therefore might magnetize a ste* j l needle, though it scarcely affected the galvanometer. This expectation was confirmed; for on substituting a small hollow helix, formed round a glass tube, for the galvanometer, introducing a steel needle, making contact as before between the battery and the inducing wiie, and then ronr.oving the needle be'ore the battery ( on' act was broken, it was fbur.d magnetized." In these experiments of Mr. Faraday, it will be observed that the secondary wire w r as no longer than the pri- mary wire, and consequently the results obtained were ex- tremely feeble; the cur.^nt obtained from the secondary wire had in fact less intensity than that obtained from the pr,mary % : no effect was produced upon the tongue, no sparks, no heat ng of fine wire or charcoal, no chemical effects ; the current was indicated on'y by the galvanometer and by its magnetic effects : no additional effect was produced by increasing the size of the battery from 1 cells to 1 20. If the coils had been unequal, the shorter used for the primary, and the longer for the secondary, >ery different results might have been obtained. This reversal What effect would have been produced had Mr. Faraday used a longer secondary coil? Who first iutioduced the use of tue kmg secondary coii ? INDUCTION TAKES PLACE 427 of the relative length of the coils was first made by our coun- tryman, Dr. Page : by making u-e of a short primary coll, and a secondary coil 320 feet in length he established the prin- ciple, that to obtain. induced currents of high intensity f.om a battery of a single or only a few pairs of plates, the induced or secondary circuit must be much longer th:m the induc'n* or battery circuit. By employing a short primary coil, and a secondary coil of copper ribbon 220 feet in length and one inch wide, powerful shocks were obtained, a Leyden jar charged, and water decomposed, by the action of the secondary current : with a coll 320 feet in length, a secondary current was obtained of sufficient intensity to pass between charcoal points before con- tact. The establishment of this principle led to the construction of several important instruments for the development of secon- dary electricity, and eventually to that of Ruhmkorff's coil. 35. The inductive elFect of the Primary current ta^ea place through a considerable distance. The inductive influ- ence of the primary current takes place even when the primary and secondary coils, are not placed one within the other, but are separated by a considerable distance. Thus in Fig. 215, let L, . 215. 9 L The Secondary Induced Current. represent one cell of a Daniell's battery ; A, the primary coil, composed of a short strip of copper ribbon, and having one of its extremities permanently connected with the positive pole of the battery, while the other is arranged in such a way that its connection with the negative pole may be made and broken at pleasure by drawing the negative wire over the ribbed piece of iron which terminates it : w, is the secondary coil, consisting of a great length of fine copper wire, separated 435. Will induction take place even if the coils are separated from each other ? How can tnis be proved ? 428 THROU&H A CONSIDERABLE DISTANCE. ^ to a considerable distance from the primary coil A, and having its two extremities connected with the handles. As the wire, connecting the primary coil with z, passes from one ridge of the piece of ribbed iron to another, the primary circuit is rap- idly completed and broken, and a succession of powerful induced momentary currents alternately in opposite directions, circulates through the secondary coil w, by which a torrent of sharp shocks are given to the moistened hands. It will be observed that the extremities of the coil \v, being connected with the handles, the body of the experimenter together with the secon- dary coil, constitutes a closed circu : t. This inductive action is * obtained even though a plate of glass be interposed between A and w, but if a plate of metal be interposed no inductive ac- tion takes place in the coil w, because it is transferred to the interposed conducting metallic plate. When the coil w contains several thousand feet of fine wire, the shocks are too intense to be endured. The intensity of the shocks, however, diminishes in a rapid ratio, as the distance between the coils is increased. With the arrangement represented in Fig. 215, shocks through the tongue are easily obtained when the wire coil is a foot or two above the ribbon toil, and the distance may be still further increased by using a larger ribbon co'l or a mo; e powerful battery. The shocks are made much more violent by wetting the hands with salt water. The intensity of the shock aLo diminishes rapidly as the secondary coil w is raised from a horizontal position into an inclined one, and when it is elevated into a vertical position, its edge resting on the primary co'l, they are no longer felt. These induced currents not only give powerful shocks, but also magnetize steel needles, and pro- duce chemical decomposition : the former may be shown by placing a sewing-needle in the centre of the coil w, when it w 11 instantly be made permanently magnetic ; and the latter by disconnecting the extremities of the coil w from the handles, and connecting them with platinum wires dipped into acidulated water, or into a solution of iodide of potassium. The charac- ter of the induced secondary current depends very much upon the arrangement of the secondary coil w: if it be primary current which actuates it being always accompanied by the production of a secondary current in the same direction with the primary, as will be more fully explained presently, 448. So great is this increased effect, that though a battery may be so weak as to be altogether unable to produce any shock or emit the ftiintcst spark when its extremities are connected by a short wire, the instant the conducting wire is lengthened and coiled into a helix, within which a rod of soft iron is placed, in consequence of the powerful induction which takes place, the Give an illustration. Explain the increased effect produced by coiling the connecting wire into a helix. Explain the increased effect on inserting a rod of soft iron iuto the helix. Give experiments in illustration. Is there any difference iu effect on making aud breaking connection? IN TIIS PRIMARY WIRE. 435 battery current on breaking contact acquires sufficient intensity to communicate powerful shocks and give vivid sparks. This is conclusively proved by the following experiments : a very small compound battery was formed of six pieces of copper bi'll-wire, each about 1J inches long, and six pieces of zinc of the same size, a battery altogether too small to give the slightest shock or the faintest spark when the poles were con- nected: the connection between the poles was then made by means of a fine copper wire one-sixteenth of an inch in diam- eter, thoroughly insulated by a cotton covering, five miles in length, and wound upon a small core of soft iron : the sho.-k on breaking connection between the poles, with this arrangement of the conducting wire, was- distinctly felt at the same moment by twenty-six persons, who had formed a circle by joining hands arid were placed in such a manner as to form a part of tlie gal- vanic circuit: the shock felt by the sam 3 persons 01 making contact with the battery, was hardly perceptible. A current is likewise produced when contact is made, but it is by no means as powerful, and is in a direction opposite to that of the ba'teiy. A thermo-electric battery which is ordinarily too weak to fur- nish sparks, can be made to do so on breaking contact, by means of a coil wound upon an iron axis. In the case of the largs magnetic helix constructed by Dr. Page, described in 426, the length of the terminal secondary or separation spark, when the battery current was broken was immense : when the bat- tery was allowed to attain its full power, the sudden separation of the wires produced sparks eight inches in leng h : when the separation was slow, the sparks were short and spread out more like flame. The effect is still further increased if the soft iron, instead of being solid, consists of a bundle of straight wires. To observe the effects of the induced extra current in the primary wire, suitable wires may be attached at A and c, Fig. 217, in place of the galvanometer: and thus it may be shown that this direct extra current gives violent shocks and bright sparks, decomposes water, melts platinum wire, and magnetizes steel needles. The brilliancy of the spark is much increased by employing a ribbon of sheet copper coiled into a spiral, in- stead of a helix of insulated wire. There is a difference in the character of the extra current when a coil of fine wire is employed, from that which is produced with a ribbon coil. In What was the length o f the spark produced by Dr. Page's large helix ? What is the effect of substituting iron wires for the solid iron rod ? IIosv may the effects of the in- duced ext-a current in the primary wire be displayed? What are tliese effects ? What is tue effect of substituting a coil of tine wire for a ribbon coil? 436 INDUCED TERTIARY CURRENTS. the former case, it is more intense, gives more violent shocks, and effects chemical decomposition more rapidly : in the latter, it is of greater quantity, gives more vivid sparks, and exerts greater heating power. These direct and inverse extra cur- rents, produced when the connection of the primary wire is broken or made, are not confined to the wire, but extend through the whole series of the battery, and increase in rower with the extent of the series. They are probably due to the sudden polarization and discharge, 312, of all the molecules in the secondary circuit, on completing connection, and to the sudden de-polarization and discharge in the opposite direction, on breaking connection. It will be remembered that they do not exist, so long as the primary current circulates continu- ously through the battery. They spring into action momen- tarily only, the instant this continuity is interrupted. 440. Induced Tertiary currents. Induced currents of higher orders. Henry's Coils. The secondary current which is induced by the primary current of the battery, may be used to induce a tertiary current, and this tertiary a quaternary current, and so on. Thus, in Fig. 218, let L, represent one cell of Daniell's battery, and A, a primary coil of copper ribbon carry- ing the battery current: let the secondary coil be placed imme- diately over it, and its two extremities be extended so as to connect with the extremities of a third coil, B : these two coils will in effect form a closed circuit, and constitute but one second- ary circuit : then immediately above B, let another ribbon coil be placed, whose extremities are extended so as to connect with the coil c : these two coils will in effect form but one closed circuit carrying the tertiary current : immediately above c, let another ribbon coil be placed whose extremities are ex- tended so as to connect with those of the coil D : these two coils will in effect ibrm but one closed circuit carrying the quaternary current : immediately above D, let another ribbon coil be placed the extremities of which are connected with the galvanometer G: these two coils will in effect form but one cir- cuit carrying the quinquenary current. When the connection of the primary coil A, with the battery is formed or broken, a current will be induced simultaneously in all the coils, but inversely in each pair. Thus, if the connection of the coil A, with the battery be completed, a secondary current of negative electricity will be induced in the coil B ; a tertiary current of pos- 440. Sho-^hovv induced tertiary currents may be produced : current of h-'^her orders. State tiio relations of these currents when the coui>ectiou with the batter/ u cstu.bli.hed : HENRY S COILS. 437 Fi S 218 - itive electricity, moving in the opposite direction, in c ; a quaternary current of negative electricity, moving in the same direction, in D ; and a quinquen- ary current of positive electricity, mov- ing in the opposite direction, in the last coil, as shown by the galvanometer. On breaking the connection of the pri- mary coil with the battery, currents will be induced simultaneously in all the coils, but in the inverse direction ; in the secondary coil they will be posi- tive, in the tertiary negative, in the quaternary positive, in the quinquenary negative. By an extension of the se- ries, currents even of the ninth order have been obtained, the successive cur- rents being alternately positive and negative, direct and inverse. These jji m coils are generally called Henry's coils, after Prof. Henry who first in- vestigated this subject. They can be made to give currents of quantity or intensity, according as they are com- posed of copper ribbon or a great length of fine insulated wire. The two currents, direct and inverse, through- out the whole series, are exactly equal in quantity. They can be induced even if the coils are con.-iderably sep- arated from each other, though the ef- fect is diminished by distance, and il even when glass plates are inter- posed, but they are destroyed by the interposition of a plate of metal in any part of the series. They progressively diminish in energy from the beginning to the end of the series. The tertiary currents may be very satisfactorily ex- hibited by introducing a second double helix, in Fiq. 214, between r, and the Henry's Coils. J when it is broken. By waom was the discovery made? Give the history of the discovery. 438 DISCOVERY OF THE EXTRA CURRENT. battery, and connecting the outer helix of the second pair, with the inner helix, p, of the first ; on every completion and break of the battery circuit, a secondary current will circulate in p, and a tertiary current in the opposite and in the same direc- t'ons alternately, will be induced in the outer coil, s, as shown by the galvanometer. Shocks may also be obtained, which may be increased by placing a bundle of iron wires within the helix, as shown in Fig. 222. In the following table the direc- tion of the successive induced currents, both at the establishment and break of the battery current are given : the sign + indi- ca:ing those which flow in the same direction as the battery cur- rent, and the sign those that flow in the opposite direction. Table of the directions of the induced currents^ up to the ninth order. At the beginning At the ending. Primary current, + -+- Secondary, + Tertiary, -f- Quaternary, + Quinquenary, -+- Sextenary, 4. Septenary, -|- Eighth order, 4- Ninth orderj + 441. History of the discovery. This induction of a second- ary current in the primary wire itself, the peculiar action of a long conducting wire, either straight or coiled into a helix, and the increase of effect obtained by a ribbon of sheet copper, were discovered in 1831, by our countryman, Prof. Henry, now of the Smithsonian Institute, and published in the 22d volume of Silliman's Journal. The investigation was continued by him in 1834, and the results were communicated to the American Philosophical Society of Philadelphia, January 16th, 1835, and were published in a circular of thai Society dated Feb. 1835, and reprinted in the Journal of the Franklin Institute, vol. XV. The same discovery was also made by Mr. Faraday, his atien- tion having been called to the primary fact of the increase of effect produced by using a long wire, and especially one wound round an electro-magnet, to connect the poles of a battery, by a young man named Willam Jenkin, and was communicated by him to the Royal Society in a paper received Dec. 18th, 1834, and read January 29th, 1835, entitled "On the influence by induct r on of the electric current upon itself." In this paper many new facts were given, but the credit of the original discov- ery in 1831, clearly belongs to Prof. Henry. MAGNETO-ELECTRIC V. Magneto-Electricity. 439 442. Blao-neto-electric Induction. The induction of a current of electricity is not limited to the primary current of the battery : a similar current is also induced by the action of a permanent magnet upon a closed wire, and also by the action of an electro-magnet actuated by a primary battery current. The former is called Magneto-electric induction ; the latter, Volta-magneto-electric induction. In the case of magneto-elec- tric induction, the conditions necessary to induce the secondary current, are as follows. There must be a closed circuit, with a galvanometer included for the purpose of indicating the exist- ence of the current, as in the case of volta-electric induction, 433, and then a strong magnet must be rapidly brought near, and removed from the closed wire. Thus, in Fig. 219, a contin- Fig. 219. Magneto-Electric Induction. uous wire, carefully insulated by silk, is wound into a helix, and i t ts two ends are connected wi f h a galvanometer in such a way as to form a closed circuit. On introducing a powerful magnet into the interior of the helix, which is made hollow for this pur- po-e, the needle experiences a violent deflection, showing the 442, What is Electro-magnetic induction ? What, is Volta-electric induction ? IIo\r can the induction of electricity by a magnet be proved ? Describe the experiments. Why must the magnet not be iutroduced more than half way ? 440 INDUCTION. production of a current of electricity in the inverse direction from that which is circulating around the magnet, according to the theory of M. Ampere, 404. The magnet beincr allowed to remain motionless in the helix, in a few moments the needle resumes a stable position; but if the magnet be rapidly with- drawn from the helix, the needle is immediately deflected, and indicates an electrical current in the wire the reverse of the previous one, but in the same direction as that in the mag- net. If the magnet, instead of being placed within the helix, be merely passed over it rapidly, the effect is the same. It is also found that in performing these experiments care must be taken not to introduce the magnet more than half way into the he!ix ; for if passed wholly through at one motion, the galvan- ometer needle is deflected, is then suddenly stopped as by a blow, and finally is deflected in the opposite direction : the move-' inent of the needle is reversed because as the magnet advances and appears at the opposite extremity of the coil, it comes at last to produce the same effect as withdrawing a magnet from a helix, when, as ha^ been stated, a current the reverse of the first is produced. It is abo found that the two poles of the magnet produce currents in opposite directions, i. e., if the north pole, on being introduced into the helix, produces a current from left to right as shown by the galvanometer, the south pole, on b^ing introduced into the same helix, will induce a current in the opposite direction, or from right to left. It is also found, that, the pole of the magnet remaining the same, the winding of the coil to the right or the left, reverses the direction of the current: thus, when the north pole of a magnet is introduced into a right-hand helix, the induced current as shown by the galvanometer, will be in the inverse direction to that which is induced when the same pole is introduced into a left-hand helix. 443. Electricity also Induced by Induced Magnetism. The same effect may be produced by the rapid making and unmaking of a magnet by means of induction. If a piece of soft iron be introduced into the helix, Fig. 219, instead of a permanent magnet, and a powerful bar magnet be brought near the piece of soft iron, so as to induce magnetism in it, we find the same result produced as would be if a perma* nent magnet, having similar poles, were introduced into the helix. In Fig. 220, if N, s, be a powerful horse-shoe magnet, and w, 5, be a piece of soft iron having a short piece of insulated What is the inductive effect of the opposite poles ? What is the effect of reversing the winding of the coil? 443. Hosv may electricity he induced by induced magnetism? How cau an electric spark be obtained from a magnet? Describe Figs. 22.0 aud 2i,l. ELECTRICITY INDUCED Fig. 220. 441 The Electric Spark obtained from a Magnet. wire wound around it, the two ends of which, a, 5, are brought together so as to nearly touch, then, whenever the piece of soft iron, w, s, is brought down on the magnet and becomes magnet- ized by induction, a current of electricity is generated in the coil, and a bright spark flashes between the extremities, a, b: a sim- ilar spark takes place whenever the soft iron bar is raised from the magnet and its induced magnetism disappears. Again, if c ill Fig. 221, be a bar of soft iron, curved and wound with wire, the two extremities of which are con- nected with a galvanometer, placed at some distance, and not seen in the figure, on bringing the powerful horse-shoe magnet, N, s, rapidly near the extremi- ties, A, B, of the > c oft iron, the bar C immediately becomes magnetized by in- duction, and at that instant a powerful deflection is made in the needle by the electrical current induced in the wire: the needle soon regains its equilibrium, but the instant that N, S, is removed, and Etectnr.it i/ 1 miitwi by induced c ceases to be magnetized by induction. Magnetism. J 442 BY INDUCED MAGNETISM. t there is a second violent deflection of the needle, showing the production of a current of electricity in the opposite direction. 444. History of the discovery of Magneto-electricity. The induction of electricity by magnetism was the discov- ery of Mr. Faraday, in 1831. His original experiment was arranged as follows. " A combination of helices like that al- ready described, 434, was constructed upon a hollow cylinder of pasteboard ; there were eight lengths of copper wire, contain- ing altogether 220 feet : all the similar ends of the compound ho low helix were bound together by copper wire, forming two terminations, and these were connected with the galvanometer. One end of a cylindrical magnet, three-quarters of an inch in diameter and eight inches and a half in length, was introduced into the axis of the helix, and then, the galvanometer needle having become stationary, the remainder of the magnet was suddenly thrust in ; the needle was immediately deflected in the manner in which it ought to be according to Ampere's the- ory : being left in, the needle resumed its former posit'on, and then, the magnet being withdrawn, the needle was deflected in the opposite direction : these effects were not great, but by intro- ducing and withdrawing the magnet so that the impulse each time should be added to those primarily communicated to the needle, the latter could be made to vibrate through an arc of 180 or more. In this experiment, the magnet must not be passed entirely through the helix, for then a second action occurs. When the magnet is introduced, the galvanometer needle is deflected in a certain direction ; but being in, whether pushed quite through or withdrawn, the needle is deflected in a direction the reverse of that previously produced. When the magnet is passed in and through at one continuous motion, the needle moves one way, is then suddenly stopped, and finally moves the other way." " Similar effects were then produced by the sudden induction of magnetism in soft iron. A soft iron cylinder was introduced info the axis of the hol'ow helix: a counle of bar magnets, each twenty-four inches long, were ar- ranged with their opposite poles in contact at one end, and then spread out ?o that their other poles might be put in contact with the extremities of the soft iron cylinder, one pole being at one extremity of the helix, and the other at the other extremity, so as to embrace the iron core, and convert it into a magnet by induction : on breaking contact, or reversing the poles, the mng- 444. Who discovered the induction of electricity by magnetism ? Describe his origi- nal experimeut. How were the helices arranged 1 ELECTRICITY INDUCED BY AN ELECTRO-MAGNET. 443 netism was destroyed or reversed at pleasure. On making contact, the needle was deflected ; continuing contact, the needle became indifferent, and resumed its first position : on breaking contact, it was again deflected, but in the opposite direction to the first effect, and then it became indifferent : when the mag- netic contacts were reversed, the deflections were reversed." 445. An Electro-magnet magnetized and de-magnetized, will induce Electricity in a closed Wire. Volta-magneto-elec- tric Induction. In like manner, if, in Fig. 214, intended to illustrate Volta-electric-induction, a bar of soft iron be intro- duced into the centre of the primary coil, then, on establishing connection with the battery, not only is there a secondary current produced in the outer coil, on completing and breaking the circuit in the primary coil, but also an additional secondary current in the same direction as the first, by the magnetization and de-magnetization of the bar of soft iron, which takes place, whenever the connection of the inner coil with the battery is made and broken. The strength of this induced current will be proportioned to the power of the battery, to the length and fineness of the secondary wire, and also to the size of the soft iron rod employed, and the power of the electro-magnet pro- duced. The power of an electro-magnet, other things being equal, depending upon the extent of surface which it presents, if the bar employed be very small, and introduced only a short distance, only a feeble electro-magnet will be produced, and a comparatively feeble secondary current generated. If the rod be large, and introduced to the extreme end of the coil, its elec- tro-magnetic power will be proportionately increased, and also the strength of the secondary current. A bundle of wires is found to produce much greater effect than a Folid iron ro;l, and this is proportioned to the number of the wires employed. This affords a very convenient mode of regulating the power of the secondary current ; commencing with one wire, the strength of the induced current will be increased by every suc- cessive wire that is added. Thus, in Fig. 222, if p represent the primary coil, s the secondary coil, and G the galvanometer, the strength of the secondary current induced by making and breaking contact with the battery, will be greatly increased with the addition of every wire that is introduced into P, indi- cated by the deflection of the needle and strength of the shocks. 445 What is the effect of making and unmaking an electro-magnet within a helix ? What is the effect of increasing the size of the soft-iron core? of using wires i ist-ad of an iron rod ? Describe Fig. 222 How can. the strength of the shocks be regulated '! 444 The strength of the Induced Current proportioned to the number of wires employed. If a bar of copper were introduced into the coil, instead of an iron bar, or wires, the current would not be stronger than if the two coils alone were employed. Thus we may make use of the electricity of the primary coil to induce both electricity and magnetism, and then employ the magnetism so induced to add to the force of the induced secondary current of electricity. 446. History of the discovery of the Induction of electric- ity by Electro-mag-netism. This was also the dis< overy of Mr. Faraday, in 1831. His original experiment was arranged as follows. "A welded ring, Fig. 223, was made of soft round bar- iron, metal being seven-eighth's of an inch in thickness, and the rinjr six inches in external diameter. Three helices were put round one part of this ring, each containing about twen- ty-four feet of copper wire, l-20th of an inch thick : they were insulated from the iron and from each other, and superimposed, occupying about nine inches in length upon the ring, or somewhat less than one-half of the circumference: they were arranged so as to be u?ed sepa- rately or conjointly. On the other half of the ring about sixty Fctraday^s Magneto-Electric Ring. 44 completed or broken, was so great MS to make the needle spin round rapidly four or five times, before What was the effect on forming connection with the battery ? on breaking connection ? on reversing the current? What was the second arrangement? Which was found to be the most powerful ? 446 ARAGO'S its motion was reduced to mere oscillation, by 1he operation of the air and terrestrial magnetism. Another arrangement was then employed, connecting our former experiments on Volta- electric induction with the present. A combination of helices like those already described, 434, was constructed upon a hollow cylinder of paste-board : there were eight lengths of copper wire, containing altogether about 220 feet ; four of these helices were then connected end to end, and then with the gal- vanometer : the other intervening four were also connected end to end, and the battery of one hundred pairs discharged through them. In this form, the effect on the galvanometer was hardly sensible, although magnets could be made by the induced current. But when a soft iron cylinder, seven-eighths of an inch thick and twelve inches long, was introduced into the paste-board tube, surrounded by the helices, then the induced current affected the galvanometer powerfully, and with all the phenomena just described : it possessed also the power of making magnets apparently with more energy than when no iron cylinder was present. When the iron cylinder was re- placed by an equal cylinder of copper, no effect beyond that of the helices alone was produced. The iron cylinder arrangement was not so powerful as the ring arrangement already described." 447. A Mag-net will induce Electricity in a body in mo- tion : and a IKEagnet in motion will induce Electricity in a body at rest. Arag-o's Rotations- If a circular disc of cop- per, M, Fig. 224, be made to revolve with great rapidity beneath Fig. 224. Arago's Rotations. a magnetic needle, w, s, supported upon a flat piece of gla^c and in the same horizontal plane, the needle will be deflected in the 447. What is the effect of a magnet upon a body in motion ? of a magnet in motion Upon a body at rest ? ROTATIONS. 447 direction of the motion, and stop from 20 to 30 out of the direction of the magnetic meridian, according to the veloc'ty of the motion. If the velocity be increased, the needle is ulti- mately deflected more than 90 : it is then carried beyond this point, describes an entire revolution, and finally follows the mo- tion, of the disc until this ceases. Conversely, if a horse-shoe magnet placed vertically be made to rotate below a copper disc suspended on untwisted silk threads, the disc will rotate in the same direction as the magnet. The effect decreases with the distance of the disc, and varies with the material : the great- est effect is produced by the metals ; with wood, glass and water, it disappears: if the action on copper be represented by 100, that on other metals is as follows: zinc 95, tin 46, lead 25, anti- mony 9, bismuth 2 : if the disc be slit in the direction of the radius, the effect is much reduced, but is restored if a connection be completed again by soldering. These rotations were first observed by M. Arago, in 1825, after whom they have been named. He also noticed that the presence of a mass of unmag- netic metal, like copper at re>t, diminishes the number of oscillations which a magnetic needle make^ in a given time : in the case of copper, the number is reduced from 3uO to 4. Mr. Faraday, in 1831, observed the converse of this, viz: that the presence of a magnet at rest diminishes the motion of a rotating mass of metal, and finally destroys it : if a cube of copper be suspended by a twisted thread, so as to rotate rapidly between the poles of an unactuated electro-magnet, it stops, the instant the electro-magnet is excited by the battery current. These facts were first explained by Mr. Faraday, in 183 1 . He showed that they are due to the secondary electrical currents which are induced in the discs of metal by the action of magnets, either the metal or the magnet being in motion. He found in all cases, that whenever a plate of conducting metal is made to pass either before a single pole, or the opposite poles, of a magnet, so as to cut the magnetic curves at right angles, electrical cur- rents are produced in the metal at right angles to the direction of the motion : in the case of the revolving disc, the direction of these currents is from the centre to the circumference, following the direction of the radii : it is to the operation of these induced currents, that the effects in question are due. The magnetic curves here spoken of, are curved lines of magnetic force which pass through the axis of a magnet, or the line joining the poles, Describe Arago's rotations. Give Mr. Faraday's explanation. What are the magnetic curves? 448 MAGNETO-ELECTHIC INDUCTION The Magnetic Curves. Fi S- - 25 - and in the same plane with this line, Fig. 225. Whenever these curved lines of magnetic force are cut by the move- ment across them of any mass of matter which is an electrical conductor, as a, b, in the Fig.) whether it be a disc, a mass of metal; or a wire, induced sec- ondary currents of electricity are produced. 448. The Magnetism of the Earth induces secondary currents of Electricity in metallic bodies in motion. Terres- trial magnetism, acting like an immense magnet placed in the earth, occupying the direction of the dipping needle, and according to Ampere's theory, 403, operating like a series of electrical currents, flowing from east to west parallel to the magnetic equator, will develop induced electrical currents in wires or metallic bodies that are moved across the magnetic axis of the earth parallel to the equator, and cutting the mag- netic curves. This was proved in 1831, by Mr. Faraday, by placing a long helix of copper wire covered with silk, in the p!ane of the magnetic meridian, directed towards the magnetic pole of the earth, and parallel to the dipping needle : by turning this helix 180 degrees around its longitudinal axis, so as to revolve the strands of the helix across the magnetic meridian, he observed that at each turn, a galvanometer connected with the two ends of the helix, was deflected, showing the passage of an electric current. The same effect is always produced by moving a wire, who-e ends are connected with a delicate galvan- ometer, at right angles across the magnetic meridian. This was beautifully demonstrated in laying the Atlantic cable at the bottom of the ocean, in a direction about due east and west : as the irregular motion of the steamship produced by the waves, drew the cable back and forth across the magnetic meridian, the secondary electrical current which it induced, inconceivably faint as it must have been, produced a perceptible deviation of the mirror and the spark of reflected light in the reflecting gal- vanometer, 418, at Valentia; so that it was literally true that Wlint effect has the magnetism of the earth upon metallic bodies in motion? How Was tuis illustrated iu la^iug tne Atlantic cable? - , CONFIRMS AMPERE'S THEORY. 449 they knew at Valentia every time the Great Eastern rolled. In this case, the ocean itself formed a part of the electrical cir- cuit, together with the cable wire, and rendered it complete. 49. lYIajncto-clectric Induction supports Ampere s the- ory. The induction of electricity by the magnet is exac:ly wh it might be expected if Ampere's theory be true, 403, 4J4, and confirms it. If, as is supposed by Ampere, magnetism is proluced by a series of electric currents perpetually circulating around a magnet in a direction at right angles to its ax's, the introduction of a magnet into the axis of a helix of insulated wire, must necessarily induce a secondary current of electricity, and its withdrawal another in the opposite direction, because the magnet corresponds to the internal helix of coarse wire car- rying the primary current, Figs. 214, 216, in the ca-eof Volta- electric induction, 433. The direction of the secondary current actually induced by the magnet, is also exactly what it should be if Ampere's theory be true. Magneto-electric induction is then, a r ter all, only a case of Volta-electric induction. It is obvious that the secondary electricity thus induced by the magnet, is not derived from the magnet, but is merely the natural electricity of the wire of the helix, which i> momenta- rily disturbed by the approach and withdrawal of the magnet. The effect is greater the longer and finer the wire, and the mare numerous the convolutions of the helix, on account of thi larger amount of natural electricity which can be oper- ated on by the magnet, and on account of the inductive action of the strands of the helix on each other, as already de-cnbed in the case of Volta-electric induction, 439. The electricity thus produced is possessed of greater intensity than that Wiiicii can be derived from any battery, however powerful, and very closely resembles the electricity of the machine in regard to giving shocks and producing light : if the circuit be broken at the moment when the magnetic induction takes place, spark; of extraordinary brilliancy will appear: it also possesses great power of effecting chemical decomposition, and may often be substituted with advantage, both for the common electrical machine and the galvanic battery. 459. Volta-magneto-electric Coils for inducing- Secondary Electric Currents. Advantage is taken of these principles in the construction of apparatus for the production of steady and apparently continuous currents of induced electricity. Thus, 449, How does Magneto-electric induction support Ampere's the >ry? What is the source of the induced electricity? Why is the effect increased by lengthening tao jire and multiplying the tiirus of the helix? 450 PAGE S in Fig. 222, if the primary coil be arranged in such a way that its connection with the battery is rapidly completed and broken, by a mechanical contrivance adapted to the purpose, at d, then so rapid a succession of secondary currents will be produced, as to have the effect of a continuous current, causing violent oscil- lations of the galvanometer needle, vivid sparks, and powerful shocks, the hands being previously moistened with salt water. The violence of these effects may be regulated by the number of wires introduced : with every successive wire, all the effects above described are proportionally increased, and when the coil is completely filled, the torrent of sparks becomes insupportable. Sometimes the regulation is accomplished by placing the coils in a horizontal position, and introducing a solid iron bar, or a bundle of wires, a shorter or longer distance. An instrument of this construction is often used by physicians for the adminis- tration of electricity to their patients. 451. Pag-c's Separable Helices. One of the niost perfect instruments for the exhibition and application of a secondary induced current, by the action of the primary current of the bat- combined with an electro-magnet, has been invented by our countryman, Dr. Page, and is represented in Fig. 226. It consists of an internal helix of coarse wire, p, of three strands, each about twenty- five feet long, and hollow in the axis, so as to admit of the introduction of a rod of soft iron, or of small iron wires. On the outside of the in- ner helix there is a second helix, s, con- sisting of from one to three thousand feet of fine wire. It is Page's Separable Helices, witk wires. made entirely sepa- rate from the interior helix, and can be removed from it. The extremities of this helix terminate in two binding cups connected with the wires, 450. How can F/'g-. 222 be altered so as to produce a nearly continuous current of electricity ? How can the violence of its action be regulated ? SEPARABLE HELICES. 451 />', n. The extremities of the inner helix are connected res, pectively with the binding cups, + and , through the iron rasp, or else through a break-piece, B, attached to the instrument. CXie of the battery wires is connected with the binding cup, , the other with the break-piece B, or applied to tlu iron rasp. The continual making and breaking the circuit in the inner coil, induces a momentary secondary current of electricity in the outer coil, alternately in opposite directions. If the two ends of the secondary coil, p and n , are brought near each other, a bright spark flashes at every break in the primary current, even when no iron wires are employed. If a rod of soft iron, or a bundle of wires, w, is introduced into the centre of the helix, the spark is very much increased, brilliant scintillations are thrown off, and the shock becomes intolerable. The iron, in acquiring and losing magnetism whenever the connection with the battery is made and broken, induces a secondary current in both the coils, which is shown in the inner coil, in the in- creased scintillations which flash from the rasp ; and in the outer coil, by the violent shocks which it imparts. Sometimes this instrument is provided with a mechanical contrivance moved by clockwork, for breaking the primary current, and in this case, none of the power being consumed in producing the me- chanical motion which breaks the circuit, a very small battery will answer the purpose. If a silver dollar and a piece of zinc of equal size be used simply for the battery, and the inner helix be filled with soft iron wires, the shock is quite severe. If the extremities of the secondary coil are separated at the same in- stant that the bat-ery current is broken, a spark will be seen, and a bright flash produced, provided these extremities are tipped with charcoal points, and held almost in contact. Water may be decomposed, if the wires are made of platinum, guarded by glass, and dipped into the liquid. The extremities of these wires shine in the dark, one constantly bright, the other inter- mi ttingly. Oxygen and hydrogen are given off in small quanti- ties at each wire, and rapid discharges are heard in the water. A Leyden jar, the knob of which is connected with the inside ccating by a continuous wire, may be feebly charged, and slight shocks rapidly received, by bringing the knob in contact with one of the cups of the outer helix, and grasping with the two hands respectively the outer coating of the jar, and a handle connected with the other cup. If a bundle of soft iron wires, w, 451. Describe Page's separable helices. How is the break-piece sometimes arranged ? Describe the eSfc3ts produced by this instrument. How may a Leydeu jar be charged! 452 THE OPERATION OF ^ be introduced into the inner coil in place of the iron rod, the effects described above are much increased. The sparks and shocks may be varied at pleasure by increasing or diminishing the number of the iron wires, the addition of only one wire producing a decided effect. If a glass tube be introduced around the iron wires, between them and the inner coil, their inductive action on the secondary coil is not d minished, but if a brass tube be introduced instead of the glass, their inductive influence upon the secondary coil will be destroyed, so far as sparks and shocks are concerned : if the tube be only partially introduced, their inductive effect will be proportionably reduced, but not entirely destroyed: the distance to which the brass tube is introduced constitutes a second mode of regulating the intensity of the shocks. The brass tube neutralizes the induc- tive action of the wires by destroying the secondary induced current, and inducing a tertiary current in both the coils, flow- ing in an opposite direction, both when the battery current is established and is broken, and these tertiary currents have the effect of reducing, if not destroying, the secondary currents, which would otherwise be induced in the coils : this is always the effect of any closed wire circuit in the immediate neighbor- hood of a helix or coil carrying the secondary induced current. As the two coils P and s, are separable, it' the outer coil s be removed, and the inner coil be so arranged as to constitute a "part of the battery circuit, which is broken at pleasure by the rasp or the revolving break-piece, the existence of the extra current, 438, shown by the increased vividness which it imparts to sparks and shocks when the battery current is broken, may be very satisfactorily exhibited; also the additional effects that, are produced by inserting a soft iron rod into the interior of the helix. This instrument has been very extensively employed by physicians for the administration of electricity to their patients, on account of the facility with which the strength of the current can be regulated, by the number of iron wires introduced, by the distance to which a brass tube enclosing the wires is pushed in, or by the distance to which the iron wires or a solid red is inserted : for greater convenience, it is usual in such experi- ments to mount the co.ls in a horizontal position. 452. The Circuit-Breaker. The effect of this instrument depends to a great degree upon the suddenness and complete- What is the effect of using iron wires instead of an iron rod ? of introducing a glass tube? a brass tube? Explain the latter effect. How i^ay the existence of the extra current be displayed by thin instrument ? What fc the arrangement of tn coils when, physicians ? THE CIRCUIT-BREAKER. 453 ness with which the primary current is broken. This is true in all cases of ihe induction of secondary currents by breaking the primary circuit. It' the primary current be not broken suddenly, b it g adually, there is a proportionate diminution in the power of the secondary current. In the ordinary modes of breaking the circuit, like the hammer break-piece of Ruhmkorff's coil, 4)3, the wires being slowly separated, there is an opportu- nity for th? primary current to pass after the connection is actually sundered, by leaping across the small interval which separates them, in consequence of the conducting power of the air, and especially for the extra secondary current flowing in the primary wire to do so, on account of its extreme intensity, as is shown by the vivid spark which appears under these cir- cuin >tances. The effect of this spark is to prolong the ex- istence of fie primary and extra currents in the inner coil, and consequently prolong the existence of the magnetism in the bundle of iron wires, and prevent them from being de-inagnet- ized as quickly as they otherwise would be. This tends to prevent that suddenness in the break of the primary current, and de-ma ^netiza ion of tli3 iron on which the intensity of the induced current depend', and greatly reduces its power : .the more sudden and com,;lc;te the stoppage of the primary current and the annihilation of the magnetism of the iron wires, the more vivid and intense the secondary current in the outer coil, and the sparks and sha?ks which it produces. To obviate this difficulty, and to promote the suddenness and completeness of t!ie break, the primary coil wire f/om one pole of the battery is made to terminate in a cup filled with mercury, whose surface is covered with a thin layer of spirits of turpentine : the wire from the other pole of the battery dips into the mercury, and is so arranged that when raised out of the mercury the current is broken, when depressed the current is established. The spirits of turpentine is an absolute non-conductor of electricity, and therefore the instant the wire leaves the surface of the mercury, its extremity being drawn up into a non-conducting medium instead of into the air, the flow of the current is instantane- ou one of similar construction was introduced in France in 1856, by Foucault, and attached to Ruhmkorffs coil. 453. Ruhmkorff's Coil for inducing 1 secondary electrical currents. One of the most interesting and extraordinary of the various machines for producing continuous secondary cur- rents of electricity, is the coil of RuhmkorfF, a philosophical instrument maker at Paris, of which a section is given in Fig. 227. The principle of this instrument is precisely the Fig. 227. Ruhmkorff '3 Coil dissected. same as the last It consists of two concentric coils of copper wire: the primary or inner coil, P, p, consisting of ten or twelve yards of copper wire, about 1-1 2th of an inch in diame- ter, coiled around two or three hundred times : and the outer or secondary coil, s, s, made of very long and thin wire, about 1-1 00; h of an inch in diameter, and from three to five miles in length, the coil being formed by 20,000 to 25,000 turns of wire, and terminating in the wire* t /* and e, which are directly con- nected with tlvj points y and x. The inner helix is coiled directly on a cylinder of card-board, forming the nucleus of the apparatus, and inclosed in an insulating cylinder of glass or caoutchouc. Great attention is paid to the insulation: the wires are not merely insulated by being wound with silk, but each individual layer is insulated from the others by a coating cf 453. Describe Ruhmkorff's Coil. How is the inner coil wound ? the outer coil? How Is insulation secured ? x DISSECTED. 455 shell-lac. The length of the secondary coil varies greatly ; in some of the larger sizes it is forty or fifty miles, and made of very thin wire : the thinner the wire the greater the tension of the secondary current . M, is a cylindrical bar composed of soft iron wires, firmly bound together, and is placed in the axis of the instrument. At p and /i, are binding screws, for establishing a connection between the primary coil and a battery composed of three or four of Grove's cells. The battery current enters at jo, passes on by the metallic band to the pillar c, thence to d ; then through , to the primary coil, p, p, and after traversing the whole length of that coil, finally rejoins the battery through n ; its course through the instrument being indicaied by the arrows. The circulation of the battery current through the primary coil admits of being broken at c and d. When rf, which is a small hammer suspended from a pivot at #, is raised, the current is broken ; when it is down, the current is contin- uous, parses on through the hammer, and after traversing the whole of the primary coil, eventually finds its way back to the battery, at n. As soon, however, as the current begins to circulate through p, p, the bundle of iron wires, M, becomes strongly magnetic, attracts d from the pillar c, and the primary current is interrupted ; the instant this takes place, M loses its magnetism, and the hammer, d, falls ; as soon as this occurs, the battery current immediately begins to circulate again, and M is again made magnetic, d is again attracted, the current is again broken, and is again renewed. The break in the current is made several times in a second, and by mechanical means may be made much more rapid. By each of these interrup- tions, a powerful secondary current is momentarily induced in the outer coil of fine wire, s, s, partly by the inductive influ- ence of the primary current itself, and partly by the influence of the magnetism momentarily induced and destroyed in the bar M, according to the principles stated in the preceding sec- tions : if there be a break in the secondary coil, as at y and x, Fig. 227, the electricity will leap across the interval with the production of vivid sparks. Every time the connection with the battery is broken, two direct secondary currents, one of positive and the other of negative electricity, are induced, moving in the same direction with the battery current. Two inverse secon- dary currents of positive and negative electricity, moving in the opposite direction from the battery current, are also induced at Describe the arrangement of the coils. How is the current broken ? IIow many cur- rents are induced at every break and completion of the circuit ? 456 THE EFFECT OF every completion of the battery current: consequently each of the po.es y and or, is alternately affected with positive and neg- ative electricity, and if equal in quantity and tension, would exactly neutralize each other. But the currents induced when the current is completed, are not equal to those induced when the connection is broken : on breaking, the current is of shorter duration and more tension; on completion, of longer duration and less tension. When the two extremities of the outer coil, y and x, are connected by- a continuous wire, the direct and inverse currents being nearly equal in aggregate power, the latter partially neutralize the former; but if the two extremities of the coil are separated at y and x, as in Fig. 227, the resistance of the air is then opposed to the passage of the currents, and only the current which has the superior ten- sion, i. e., the direct current produced by breaking connection, and moving in the same direction with that of the battery, is able to leap over the interval and effect a passage : the sepa- ration of the two currents is more complete the greater the interval, up to a certain point, when' neither pass, and there is then nothing induced at the poles y and x, but electrical tensions alternately in contrary directions. Consequently, in Fig. 227, as it is the direct current corresponding with the battery cur- rent only that passes between # and x, y must be taken as the positive pole, and x as the negative pole, because they discharge intermittent streams, the one of positive and the other of neg- ative electricity exclusively. These currents are of extreme intensity, and produce vivid sparks which succeed each other in continuous succession. The intensity of these sparks may be greatly increased by increasing the suddenness with which the continuity of the primary current is broken. 453.* The Condenser. Its effects explained. The power of the instrument may also be greatly increased by attaching to the primary co 1 a modification of the Ley den jar, called a Condenser. This consists of 150 sheets of tinfoil about 18 inches square, exposing a total surface of about 75 square yards. These sheets are pasted together so as to form two large sheets, and then attached to the two sides of a sheet of oiled silk, which completely insulates them, thus forming in effect a very large ]>yden jar. They are then coiled several times around each other, so that the whole can be packed beneath the base of the instrument. One of these sheets, the positive, is connected with the binding cup ri, Fig. 227, so as to communicate with Explain why the direct currents alone can force a passage. How may the vividness of the sparks be increased ? What is the arrangement of the condenser ? What ellect THE CON'OEXSER. 457 the primary current when it passes into the primary coil ; the other, the negative, is connected with the binding screw p whk'h communicates directly with the battery current : these correspond with the binding screws G and H, in Fig. 228. The operation of this instrument seems to be as follows. We have seen, 439, that, at each break of the battery current, an induced extra-current in the same direction is produced in the pri- mary coil itself; and it is this which produces the spark that passes at each moment between the hammer and the anvil: being in the same direction, and prolonging the existence of the direct current in the primary coil, it tends to prolong also the magnetic effect, and to prevent the bundle of soft iron wires from being de-magnetized as quickly as it would be otherwise. By attaching the condenser to the primary current, the extra current, instead of producing a strong spark, darts into the con- denser, the positive electricity into one sheet, and the negative into the other : they then combine quickly by the primary coil, by the baflery, and the circuit, H, L, Fig. '228, and in so doing give rise to a current in a direction opposite to that of the prima- ry current, wlrch instantly de-magnetizes the bundle of toft iron wires, and renders the break of the primary current much more sudd a n and complete. Tue peculiar action of the condenser u )on the coil by the absorption of the extra current, was discov- ered by Fizeau at Paris in 1853 : by connecting the plates of the coaden^er with each side of the circuit-breaker, he found that the sparks discharged at the hammer by the extra-current were diminished, while those of the outer coil at y and #, were dojble 1 in length. It was soon attached to the coil by Ruhm- koivf, and the intensity of the secondary current so exalted as to lengthen its spark fro'ii one-eighth to a little more than half an inch. This was the first great improvement made upon the coil as constructed by Dr. Page. Other improvements were added in 1856 and 1857, by means of which the power of the in- strument wa> gradually increased, until finally sparks of extreme intensity, from eighteen to twenty inches in length, were obtain- ed iron the secondary coil at y and x. The rapid de-inagnet- iz ition is also greatly accelerated by making usa of a bun-J * of iro i wire? instead of a solid bar of soft iron. This improve meat was made by Dr. Page in 1838, in the construction of hi.-, scparab'e helices, 451 : this effect seems to be produced in great part by the neutralizing influence of the similar poles of the lists it upon the extra current spark ? Upon the spark of the secondary coil 1 Explain it operation. Who discovered this fact I What effect is produced upon the suddenness of de magnetization by the use of iron wires 1 458 RUHMKORFF'S COIL COMPLETE. wires on each other. Thus it appears that by the coils of Page and Ruhmkorff, galvanic electricity of low tension may be u-ed to induce statical electricity as intense as that of the ordinary electrical machine, while its quantity is far greater; so th:it they may be substituted with great advantage for that machine in most cases, where a continuous discharge of sparks and shocks is required. 454. Ruhmkorff's Coil complete. The same instrument is represented in relief, in Fig. 228 : K, represents a milled handle Fig. 228. Coil complete. by which the cylinder L, called the Commutator, consisting of alternate pieces of copper and ivory, is turned so as to bring either piece into contact with the metallic spring o and re- verse the direction of the primary current through the coil, by connecting at pleasure with the positive or negative pole of the battery : A, is the binding screw through which the posi- tive current from the battery enters, and there is another on the opposite side of L, not seen in the Fig., for the passage of the negative current : from A, the positive current passes up the spring o, into the commutator L, by which it is transmitted to the commencement of the primary coil, making its exit at I : it then proceeds to the hammer D, through N, to the binding cup H, whence it returns to the negative pole of the battery: M, is the bundle of soft iron wires, occupying the core of the instrument: Y and x, are the binding screws connected with the extremities of liie outer or secondary coil, and which may Inscribe KuhmkorlT's Co:', as represented in Fig. 228. RITCHIE'S 459 be brought into connection with each other by wires, as at y and a:, in Fig 227 : the condenser is attached at G and II. On turning the handle K, so as to bring the metallic piece L into contact with the spring o. the primary current immediately circulates through the inner coil, and a shower of vivid sparks flashes continually from x to T, when the proper connections are made by wires nearly touching each other. With largo coils the hammer cannot be used, on account of the extreme violence of the spark produced by the extra-current; tin surfaces become so much headed as to melt : to obviate this difficulty, and to promote the suddenness and completeness of the break in the circuit, a mercury circuit -breaker, 452, has been invented, by which the power of the instrument has been greatly increased and the use of the hammer discontinued : more recently, mechanical means have been employed for breaking the circuit slowly or rapidly, at the pleasure of the operator : by these and other improvement-, this very interesting and re- markable instrument has been brought from a comparatively feeble state to a very high degree of efficiency, by our country- man, Mr. Ritchie, a philosophical instrument maker at Boston. 455. Ritchie's improved RuhmkorT Coil. The length of the secondary spark which Ruhmkorff obtained i:i his original coil, did not equal one inch: in 1857, Hoarder, in England, by more carefully insulating the coils, obtained sparks of three inches : it was found impossible to make larger and more pow- erful coils, in consequence of a discharge taking place within the coils, the current forcing a passage from strand to strand between the outer and inner portions and breaking down the insulation, the successive layers of wire being only separated by insulating media ; and the longer and finer the outer coil, the stronger is the tendency for the secondary current to force a passage laterally through the adjoining layers in preference to passing through the immense length of the secondary wire, amounting in some cases to eighty miles. In 1857, Mr. Ritclve devised a mode of winding the wire of the outer helix in sev- eral different sections, carefully insulated from each other : the first section commences near the axis just upon the outside of the primary coil, and gradually extends to the outer circum- ference, in a plane perpendicular to the axis, (in the m :um"i* that sailors coil ropes on the deck) ; then continues to the next section, which is carefully insulated from the first, and wound from the outer circumference to the inner, and so on altern- Describe Ritchie's improved Ruhmkorff Coil. 460 IMPROVED a'e'y from sec 'ion to section, until the coil is completed: in this manner, in consequence of the division of the outer coil in:o many section.?, and their very perfect insulation, it be- comes impossible for the secondary current to force a lateral pa ?age and break through the coil. The result was, that, in 1837, coils were ma le which gave sparks of twelve and event- ually sixteen inches, in place of three. The instrument con- sists of a primary coil of copper wire about 1-Gth of an inch in d'ameter and about 150 feet in length, wound in three courses, very carefully annealed, and mounted vertically," as in Fig. 229 : thio coil is completely covered externally with gutta- Fig. 229. Ritchie's Improved Ruhmkorff Coil. pcrchi ^Olhsof an inch in thickness, and passing entirely through the basement to a plate of the same substance, to will- h it is united: within this coil is placed the bundle of soft iron wires : over the primary coil and magnet a thick glass cyl- inder or bell is placed, closed at the top, and provided with a knob by which it 'can be raised from its position. On the out- RUHMKORFF COIL. 4^1 side of this glass bell is placed the secondary coil, consisting of very fine copper wire, about 1-1 00th of an inch in diameter, very carefully insulated by silk winding, from three to thirty, and even eighty miles in length, wound in the manner above described, upon a cylinder of gutta-percha : the extremities of this coil are enclosed in rubber tubes and carried to insulated glass pillars, from which the induced current is taken by plati- num wires in whatever direction it may be required : in Fig. 229, it is conveyed to the electric Egg, for the purpose of exhibiting its extraordinary illuminating power when discharged through a vacuum. The condenser is made of tin-foil pasted on tissue paper, of three thicknesses between each stratum : it is composed of three sections, of 50, 100, and 150 feet, which by means of screws can be used separately or in combination ; this is packed beneath the basement and directly connected with the binding screws of the circuit-breaker. The interrupter, or circuit- breaker, is raised by means of a small crank worked by hand, operating upon a ratchet wheel, whose teeth strike the extremity of a delicately adjusted lever, from the other end of which the hammer is suspended : the rapidity of the break in the circuit may be varied at pleasure by turning the crank slowly or rap- idly : the battery current is derived from two to four cells of Bun- sen's carbon battery. When the crank is turned very slowly, the connection of the primary coil with the battery is prolonged, and the bundle of iron wires becomes very highly magnetized : the break thenoccurs very suddenly, and instantaneously develops the entire force of the secondary current, producing sparks of freat length and density, the discharge being surrounded by a ind of burr : if the velocity of the rotation be gradually in- creased, the spark assumes the luminous appearance of the sparks of the electrical machine : if the velocity be still further increased, the luminous discharge will disappear, for there will not then be sufficient time, between the establishment and break of the connection with the battery, to magnetize the iron core on which the intensity of the induced secondary current chiefly depends. The power of this instrument is vastly greater than that of any electrical machine ; sparks of more than twelve inches in length can easily be obtained, discharges can be made so rapidly as to appear continuous, and a Leyden jar can be charged and discharged with so much rapidity as to exhibit hardly any perceptible interval, and with a noise almost stunning. -How is the circuit-breaker of Ritchie's machine arranged ? What is the effect upou the power of the instrument ? 462 THE CHARGING OP This machine of Ritchie's excited much attention in Europe. It wa> exhibited by Gassiot, before the Koyal Society, London, in 18-)8, arid by McCullough, at Paris, in Ic'sGO. Its mode of winding was almost immediately adopted by Ruhmkorff, and the secondary coil still further lengthened, amounting in some cases to 100,000 French metres, or even more, from sixty to eighty miles,^and projecting sparks two feet in length : this took place in 1860; and in 1864, he received as a reward the prize of 50,000 francs offered by the French Emperor in 1852, for the most important discovery connected with the develop- ment of electricity. 456. The management of Ruhmkor T's Coil. The charg- ing- of a Leyden jar. The principal steps in the improvement of induction coils, as first constructed, are the increased length and fineness of the secondary coil, the employment of soft iron wires instead of the iron bar in the inner coil, and the spark- arresting circuit-breaker, all inventions of Dr. Page : the discovery of the effect of the condenser by Fizeau, and its application by Ruhmkorff; and the peculiar mode of winding, combined with very perfect insulation, devised by Ritchie : to the combined effect of these various improvements, made through a series of many years, the extraordinary power of Ruhmkorff's coil, in its most perfect form, is due. Several coils may be combined so as to increase the quantity of elec- tricity which they will furnish, by placing them side by side and connecting them by wires in such a manner that the bat- tery current will circulate through the primary helix of each coil in succession, thereby forming in effect one long pri- mary coil: as only one hammer is required for the purpose of breaking the current, the remain'ng hammers should be removed : in like manner the secondary coils should all be connected by wires, so as to unite all the positive poles together into one pole, arid all the negative poles into the other : the extreme positive and negative poles may then be brought together for the purpose of displaying the effects of the instru- ment in the usual manner : by this arrangement the quantity of electricity will be greatly increased, but no increase in the tension of the current will be obtained. If an increase of ten- sion is required, each secondary circuit must be connected in a regular series, the positive pole of one to the negative pole of What improvement was made by Ruhmkorff? with what result? 456. State the suc- cessive improvements. How may coils be combined so as to increase the quantity of the current ? the tension ? ^ A LEYDEN JAR. the next, so as to form in effect but one secondary coil, each pri- mary coil being excited by a separate battery. A Leyden jar may be charged by connecting the outer coating, Fig. 230, with Fig. 230. Tlie charging of a Leyden jar by Ruhmkorff^s Coil. one of the poles of the coil, and the inner with one of the arms of a discharger, the other arm of which is in communication with the opposite pole of the coil : the extremities of the discharger should be placed two or three inches apart : after a few sparks have passed, the jar may be removed and discharged in the usual manner : with a large instrument an electrical battery containing several jars, and exposing ten square feet of surface, may be charged to saturation in a few seconds, and far more rapidly than by an ordinary electrical machine. If instead of the above arrangement, the outer coating of the jar be connected with one pole of the coil, and the inner with the other, the poles of the coil being at the same time connected by wires set about one inch apart, the Leyden jar will be constantly charged and discharged without cessation, the discharge taking place as a spark two or three inches in length, very bright, and produc- ing a'n explosive sound, which seems to be continuous. If a platinum wire be twisted around the knob of a Leyden jar, and its ends be brought near enough to the poles of the secon- dary coil to almost touch them without quite doing so, a noise- IIow can a Leyden jar be charged ? What experiment may be tried with the coil ami Leaden jar ? VVhat Is the effect of charging large electrical batteries by cascade ? 464 THE EFFECTS OF RUHMKORFF'S COIL. -"i less spark of feeble light will pass from each pole to the end of the platinum wire nearest it, at both interruptions ; if now the outer coating of the jar be connected with one of the secondary poles, the spark, at the interruption on that side, will suddenly become brilliant and noisy : the noiseless spark will kindle paper or other combustible objects, while the noisy flash from the Leyden jar will fail to kindle them. With Ruhmkorff's large coil, electrical batteries may be charged and discharged with a continuous and almost deafening noise. The most brilliant ef- fects are produced by charging a series of jars by cascade. When six jars, each containing about two square feet of coat< d glass, are employed, a continuous stream of dazzling light six inches in length, is produced, accompanied by a noise that speedily becomes almost intolerable. With one jar, the dis- charge spark is two and one-half inches long ; with two jars, three and a half inches ; with three jars, four and one-quarter inches ; with four jars, five inches ; and with five jars, five and a half inches. 457. The Mechanical effects of Ruhmkorff's Coil. The effects of Ruhmkorff's coil are vastly more intense than those of the battery, and may be classed under the heads, Mechani- cal, Physiological, Heating, Luminous, and Chemical. The mechanical effects of the secondary current produced by this coil are disruptive in their character, and resemble those of a flash of lightning. For this reason it should be passed through glass vessels with the greatest caution. With the largest appa- ratus, glass plates two inches thick have been perforated. It should not be used for firing Eudiometers, except with the greatest care and the employment of a very small battery. 458. The Physiological Effects. The physiological effects are extremely intense. The shocks are so powerful, that oftentimes careless experimenters have been prostrated by them. With two of Bunsen's cells attached to the primary coil, hares and rabbits have been killed, arid a somewhat lar- ger number would be sufficient to kill a man. 459. The Heating- Effects. The heating effects are intense. If a thin iron wire be stretched between the two points y and x, it is immediately melted and burned with a vivid light: if each of the poles y and x, be terminated with a fine iron wire, whose extremities are brought near enough together almost to touch, Fig. 231, the wire connected with the negative po-e will melt into a little globule of liquid iron, while the other will 457. What are the Mechanical effects of the coil? 458. What are the Physiological effects ? 459. What are the Heating effects ? Is there any difference in the temperature THE HEATING EFFECTS. 465 T/ie heating effects of the poles of Ruhmkorff's Coil. Fig. 232. 231< remain cold enough to be held in the fingers, Fig. 232, and if a re- flection of these points be thrown upon a screen by means of Duboscq's electric lamp, Fig. 1 60, a cone of vapor will appear to issue from the point of each wire, but that from the negative wire being the most powerful, apparently beats back the heated stream from the positive wire. These ef- fects are the reverse of those produced in the voltaic arc of the galvanic battery, in which the greatest dispersion of matter and the highest temperature, are observed to occur at the positive pole. The heat is sufficiently in- tense to inflame all combust- ible substances, and to fuse and burn metals. Great use is made of this in Spec- trum analysis, 285, 6, 7. Another very remarkable effect of Ruhmkorif 's coil, first noticed by Dr. Page, is the ignition of disintegrated conductors : shreds of metal and other conducting substances in a pulverulent condition, are ignited and fused : a very small machine will ignite a pencil mark of plumbago, even through many miles of wire, and shreds of iron over an inch in length. Advantage has been taken of this in the construction of fuses for firing gunpowder in blasting, and in the discharge of fire-arms. A fuse has been invented called from its inventor, Statham's fuse, which depends upon the ig- niting action of the current upon the sulphide of copper. It has been found that in a copper wire covered with vulcanized gutta-percha or india-rubber, a layer of sulphide of copper forms, after some months, at the point of contact of the metal and its coating, which is sufficient to conduct the current. If a por- of the poles ? Which is the hotter ? How do the poles appear, when seen by Dnhoscq's lamp ? How do these effects compare with those of the battery ? What is the degree of the heat ? What effect is produced upon shreds of metal ? One pole cold. 466 STATIIAM'S FUSE. tion of the coating be removed from a wire loop, Fig. 233, and Fig. 233. Statham^s Fuse. a quarter of an inch of the wire cut away, the current, inter- rupted at a and b, finds a passage by means of the sulphide of copper, which it ignites, and any inflammable substance like gunpowder or gun-cotton, placed in this cavity, takes fire. A very powerful battery would be required to ignite such a fuse, but with RuhmkorfPs coil, only one or two of Bunsen's ele- ments are required, the ends of the secondary helix being connected with A and B. This fuse has been very successfully employed in exploding mines in the works at Cherbourg, in France: six mines were simultaneously fired at" a distance of 1,500 feet from the apparatus. Recently a more sensitive priming material has been introduced, consisting of ten parts of sub-phosphide and forty -five of sub-sulphide of copper, and fif- teen of chlorate of potash, finely powdered in a mortar, with the addition of sufficient alcohol to moisten it throughout : the mix- ture is dried and preserved until required, in close vessels. The magneto-electric machine to be presently described, 467, is now generally employed for firing such fuses, and it is stated that one such machine contained in a box of a cubic foot in size, worked by hand, in a telegraph office in Washington, has exploded a cartridge of powder in an office in New York, over 200 miles distant. Another very common application of Ruhmkorff's coil, is to the simultaneous lighting of theatres and large halls, by the discharge of the current through platinum points placed in the gas-jets. 460. The Luminous Effects. The Luminous effects of Ruhmkorff's coil are also very extraordinary, and vary as they take place in air, in vacuo, or in very rarefied vapors. In the air, a very bright and loud spark is produced, which, with the coils of the largest size, has a length of eighteen or twenty Describe Statham's fuse. What applications are made of these fuses ? 460. Describe the Luminous effects of Ruhmkorff 'a coil in air : in vacuo. THE LUMINOUS 467 'inches. If the discharge be made to take place in vacuo, in an exhausted receiver, an extremely beautiful auroral light is pro- duced, extending through an interval of one or two yards. The experiment is made by connecting the two wires of the secon- dary coil with the extremities of the electrical egg, Fig. 229. This is screwed upon the plate of an air pump, and a vacuum, as complete as possible, produced. As soon as the sparks are allowed to pass, a beautiful luminous trail is observed to flow from one knob to the other, Fig. 234, No. 1, the negative ball The Luminous effects of Ruhmkorff'^s Coil. is surrounded by a quiet glow of light, whilst a pear-shaped luminous discharge takes place from the positive ball; between the two is a small interval, nearer to the negative than the pos- How is the experiment performed? Describe No 1, in Fig. 234. 468 EFFECTS IN VACUO itive ball which is not luminous. The discharge is constant, and as bright as that obtained from a powerful electrical ma- chine. When the exhaustion of the receiver is very perfect, the luminous portion is traversed by a series of dark bands or arches concentric with the positive ball, Fig. 234, No. 2 : the presence of a little vapor of phosphorus renders these dark bands much more distinct. If the finger be applied at the side of the egg, the connection of the lower knob with the negative pole of the coil being broken, the trail suffers a curious devia- tion, and is drawn towards the finger, Fig. 234, No. 3. The positive pole possesses the most brilliancy, and its light is red, like fire, while that of the negative pole is feeble, and of a violet color. If, instead of using an electric egg, the receiver of an air pump be employed, containing a tumbler made of Uranium glass, lined with tin-foil about half-way up the in ide, and a metallic rod be passed, air-tight, through the top of the jar, until it touches the metallic lining on the inside of the tumbler ; then, on connecting one pole of the coil with the plate of the air-pump, Fig- 235, and the other with the sliding rod, a beautiful and continuous cascade of Fig. 236. electric light will pour over the edge of the tumbler upon the metallic plate of the pump. The effect is heightened if the tumbler be placed upon a glass dish wash- ed over with sulphate of quinine : a blue fluorescence will be produced which will contrast well with the yellow glass. By introducing the vapors of different substances and different gases, the light of the electric egg is entirely changed, and a very curious stratified light produced, varying with the substance employed. The best method of procedure, is to seal The Uranium Glass. wires of platinum into the extremities of a glass tube, introduce the gases, and then exhaust the tube more or less completely. Thus, if a long wide glass tube, Fig. 236, containing sticks of caustic potash, at P, be filled with carbonic acid gas, and exhausted by the air-pump, the residual carbonic acid will then be absorbed by the potash, and the vacuum thus made very nearly perfect. The effects observed on connecting the wires + and , with Describe No. 2 : No. 3. What is the effect of using an Uranium glass ' effect of employing the vaeua of different gases? What is the OF DIFFERENT GASES. Fig. 236. 469 Luminous effects of Ruhmkorff's Coil in a vacuum of Carbonic Acid. the poles of the secondary coil of Ruhmkorflf, vary with the perfection of the vacuum. If it be merely that which can be produced by an ordinary air-pump, no stratification is obtained, and only a diffuse lambent light fills the tube ; if the rarefaction be carried a step further, narrow striae, like ruled lines, traverse the tube, Fig. 237, No. 1 : a further rarefaction increases the Fig. 237. + ? \'\ (>--">', . . . i i i i i &'/ KuJankorff : 4 interesting as showing that the ozone which is coil. Fig. 241. Fig. 242. Conversion of Air ints Nitrous Arid, by RukmkorJf'aUoil. How do electricity of intensity and quantity differ in decomposing power? What i* the effect of the coU on Air ? on Oxygen ? 47$ EFFECTS OF found to exist in the air, may also be due ta the action of electricity on the atmosphere. The passage of the . s pa:k through compound gases and vapurs, is attended by a par- tial separation of their component elements: in the case of steam, oxygen appears at the positive pole, and hydrogen at the negative ; and long sparks are found to be more effectual in producing decomposition, than short ones. Thus, in Fig. "243, Fte. 243. Decomposition of Steam by Rukmkorff's Coil. A, is a half-pint flask, with a cork in which three holes are bored; in one of these is inserted the glass tube B, which dips beneath the lower end of H, in the tough of water c; in the others, the gla^s tubes D and E, are inserted, enclosing platinum wires projecting about one inch into the flask, and appi cach- ing within 1-1 6th of an inch of each other, FO that the spark may readily pass between them: D and E, are connected by wires with the poles of Ruhmkorff's coil R. The water in the flask is boiled about fif een minutes, until all the air which it contains has been displaced by steam ; when this is the cafe, the bubbles of steam will condense in c, and no bubbles of air rise into the inverted tube H, filled with water : if at this mo- ment, the water still boiling, the commutator of the co'l be turned so as to establish a connection with the battery, spaiks will flash through the steam in A, decomposing it, and filling the tube H with a mixture of oxygen and hydrogen, which may be tested' by clo-ing the tube with the thumb and applying a lighted mntch ; a sharp detonation will take place. The power < ? the secondary induced current in effecting the combination or decomposition of gases and vapors, is much greater than that What is the effect on the vapor of Water ? Describe Fig. 243. THE COIL. 477 r of the ordinary cylinder or plate electrical machine. As the condenser simply increases the intensity of the electricity of the secondary wire, and not its quantity, no gain in the amount of the substance decomposed is effected by its use. 465. The conversion of Carbon into the Diamond by the long-continued action of the Coil. M. Despretz, who for a long time has been engaged in experiments upon the effect of heat on carbon, is said to have succeeded in converting carbon into diamonds by the action of the induced current of Ruhm- korff's coil. He fastened a small piece of sugar, which, as is well kno ,vn, contains a large amount of carbon in a state of ab- solute purity, to the lower positive ball in the electric egg, and to the upper ball a tuft of very fine platinum wire for the pur- pose of catching the sublimed carbon. A vacuum was then produced and the electric current allowed to traverse the appa- ratus for several months. At the end of this time the plati- num wires were found to be covered with fine black powder, in. which were discovered traces of crystallization. Among these crystals, ,<=ome were found of a black color, others were perfectly translucid, and were found* to be regular octoedra of a pyramidal form. When examined by a lapidary, they were found to be possessed of all the properties of the diamond. Rubies were very quickly polished with their powder, and the crystals burned in air without leaving any residue. 465. Magneto-Electric Machines. The principles on which they depend. These are machines for generating cur- rents of electricity by the revolution of coils, in front of the poles of powerful permanent or electro-magnets. In Page's and Ruhmkorff 's colls, the secondary current is produced partly by the inductive influence of the primary current, and partly by that of the electro-magnet. In the magneto-electric machine, the electric current is produced by the inductive influence of powerful permanent magnets. By bringing a magnet near a coil composed of fine covered wire and forming a closed cir- cuit, it has been shown, 442, Fig. 219, that a momenta 1 "" 1 current of electricity is induced ; and again, that when such magnet is removed from the coil, another momentary current, in the opposite direction, is induced. It has also been stated, that the two poles of the magnet induce currents in opposite di- 465. What is the effect of the coil on Carbon? Describe Despretz' experiments. 466. What are Magneto-Electric Machines ? How is the Electric current produced? 478 MAGNETO-ELECTRIC rections, i. e., if the north pole of the magnet be introduced into the coil, Fig. 219, and a current observed to flow from left to right, as shown by the galvanometer, and then the north pole be withdrawn and the south pole be introduced, a current of elec- tricity will be induced in the opposite direction, or from right to left : moreover, that these effects are reversed if the direction of the winding is changed ; i. e., if the north pole of the magnet be introduced into a right hand coil, the current will be in the inverse direction to that which is induced when the same pole is introduced into a left hand coil: if the south pole of the magnet be employed instead of the north pole, the same results follow ; so that if two coils are wound in the same direction, and placed side by side, and a north pole of a magnet be introduced into one coil, and a south pole into the other simultaneously, a current will be induced in each coil, in opposite directions : but if the coils are wound in opposite directions, and a north pole bo introduced into one, and a south pole in'o the other at the same moment, a current will be induced in each in the same direction. This is equally true, if instead of introducing permanent mag- nets into the coll-, these are wound upon soft iron cores, and then the cores are magnetized and de-magnetized by the inductive ac- tion of powerful permanent magnets suddenly brought near and removed from their extremities. Consequently, if a coil of fine insulated wiie be wound u|*>n a core of soft iron, and a powerful permanent magnet be presented to one extremity of the iron core, first by one pole, and then by the other, the soft iron will become magnetized and de-magnetized, upon every approach and removal of the magnet ; and a current Fig. 244. of electricity made to circulate through the coil, first in one direction and then in the other. If there are two such pieces of soft iron, with coils wound in opposite directions, and having the ends of the wires soldered together so as to form, in effect, but one closed circuit, and the north and south pole of a horse-shoe magnet be presented at the same moment to both, they will become oppositely magnetized, and a momentary current of electricity in the same direc- tion be induced in each coil at every ap- Why imist the coils be wound in opposite directions ? Describe the successive effects which take place when the wound armature, c, Fig. 244, is made to' revolve. MACHINES. 479 proach and removal of the magnet. If, then, in Fig. 244, N and s be the poles of a powerful magnet firmly fixed, and C, a horse- shoe armature, wound with two coils of fine wire in opposite directions, having 'their ends connected so as to form a closed circuit, and arranged to revolve about a vertical axis, so that A, after half a revolution, will be above s, and B above N, it is evident that so long as the armature is at rest, it is magnet- ized by the inductive influence of the permanent magnet, the po!es being reversed ; but the instant the armature beg'ns to revolve, it is de-magnetized, and a momentary current of elec- tricity is induced in the coils, which entirely ceases by the time it has made a quarter-revolution. Were the coils wound in the same direction, the momentary currents circulating in each, would move in opposite directions ; but as they are wound in opposite directions, momentary currents in the same direction arc induced in both. As the armature moves beyond the quar- ter-revolution, and its extremities approach the poles of the permanent magnet, they again become magnetized by induction, and it inii>-lit be supposed that an electrical current would be induced in each coil, in a contrary direction to what it was in the first quarter-revolution, because, as we have seen, the currents induced by removing the magnet from a coil and restoring it, are always in the opposite direction ; but as the extremities of the armature are now approaching reverse poles, this effect is neu- tralized, and the new currents of electricity induced in the coils in the second quarter-revolution, are in the same direction with those in the first quarter, so that in making half a revolution each coil experiences the induction of two currents of electricity in tho same direction, in consequence of receding from and approaching opposite poles, alternately in the two quarter- ro volutions, at the same moment. In the second half -revo- lution, two currents of electricity are induced in the same direction in each coil, but directly opposite to those induced in the same coils in the first half, because the coils are now receding from and approaching the reverse po!es, N and s hav- ing interchanged places in reference to A and B. Consequently, if c. were made to revolve continuously around N and s, a suc- cession of currents, in opposite directions, in each half -revolution alternately, would be made to circulate through both coils. In order that this effect may be produced, it is necessary, as has been stated, that the ends of the coils should be connected at How many currents are induced in every half-revolution ? Why may these be re- garded as only one current ? What is the final result ? 480 SAXTON'S both their extremities, so as to form a closed circuit ; and on introducing a galvanometer into this circuit, these effects may be traced by the oscillations which are imparted to the needle. The currents thus induced are primary currents, and are not sufficiently intense to produce powerful shocks. For this pur- pose it is necessary that the circuit be broken at the exact mo- ment in each half-revolution when the induction of the pri- mary current takes place. This break in the primary current produces in the coils a direct extra-current, 438, of extreme intensity, moving in the same direction as the primary, and greatly increasing its power. When this extra current thus induced, is transmitted through the body, the shocks become almost insupportable, and if directed through carbon points, the sparks acquire great brilliancy. For the production of chemi- cal decomposition, however, the primary current is sufficiently powerful, and no break in the circuit is required. These effects are manifested both at the removal and approach of the coils, but more vividly at the removal than at the approach, and their vividness is proportioned to the suddenness of the break in the circuit, and the rapidity of the revolution of the coils. 467. Saxton's Magneto-Electric Machine. The first mag- neto-electric machine for the production of continuous currents of electricity, was made by M. Pixii at Paris, in 1832 : it con- sisted of two coils of insulated wire wound upon iron cores, in front of which, the poles of a powerful magnet were made to revolve with great rapidity. In 1833, Mr. Saxton, of Phila- delphia, invented a machine of much greater power than that of Pixii, in which a curved armature with its coils, like that represented in Fig. 244, was rapidly revolved before the po'es of very powerful permanent magnets. It is represented in Fig. 245, and a section of the armature and its coils in Fig. 246. It consists of a powerful horse-shoe magnet, M, placed horizon- tally upon one of its sides : in front of its poles, and as clo-e to them as possible, without actual contact, an armature of soft iron is made to revolve upon a horizontal axis, which admits of being turned with great rapidity by means of a cord passing over a multiplying wheel, w. This armature consists of a curved piece of iron of such a shape that its two extremities, a and b, are at the same distance apart, as the two poles of the magnet, and each carries a coil of very fine wire, c and ?, careiully insulated. The two extremities of the wires which form the Why must the continuity of the circuit be interrupted in order to display the cur- tents 1 Is the effect more powerful on the approach or removal of the coila ? MAGNETO-ELECTRIC I Fig. 245. 481 Saxton's Magneto-Electric Machine, Fig. 246. Armature and Coils of Saxton's Machine. ^rminations of the coils, h and #, are united and soldered to a piece of copper passing through the axis' of the spindle on which the armature rests, but insulated from it, and termi- nating in the copper cross-piece, &, which, at every half-revolu- tion clips into the mercury cup, /, and immediately emerges from it again, thus breaking and completing the circuit once in every half-revolution; the other ends of the coils, eand/, are soldered to the spindle it?elf, and terminate in the circular disc of copper, t, which revolves in the mercury cup, m, thus maintaining a 437. Describe Saxton's Machine. How many currents are produced at every revolu- tion of the coils ? 482 MACHINE. constant connection between it and the extremities of the wires which form the commencement of the coils. The two mercury cups, I and m, are insulated from each other, but may be con- nected by a curved wire. This curved wire being inserted, it is evident that when either of the ends of k are immersed in the mercury cup, /, a closed circuit is formed, of which the coils and the two mercury cups form parts, and that whenever the cross- piece emerges from the mercury the continuity of the circuit is broken, and the extra-electric current has an opportunity to mani- fest itself. The cross-piece, k, is so arranged that its ends shall emerge from the mercury and break the circuit at the moment when the coils have just left the poles of the permanent mag- net to which they have been opposed. Under these circum- stances, if the wheel, w, in Fig. 245, be rapidly turned, four momentary currents of induced electricity, two negative and two positive, which may be regarded as, in effect, but two, one negative and the other positive, will flash through the wires in opposite directions, at every revolution ; and these will be made manifest by bright sparks of light whenever either arm of k emerges from the mercury cup, /. If the wire connecting the insulated mercury cups be removed, and wires inserted inio them, connected with the two metallic handles, H, H, which may be grasped by the hands, then these handles and the bystander become a part of the closed circuit, and at every revolution of the coils, four currents of electricity, in opposite directions, the first two in one direction, and the second two in the opposite, will flash through his body, producing an insup- portable torrent of shocks. If the wires leading from the two mercury cups be attached to a galvanometer, the needle will be violently deflected, twice in each revolution, first in one direction, and th'-n in the other, by the two opposite cur- rents. If they be tipped with platinum, and dipped in!o a solution of acidulated water, this will be decompo-ed, oxygen set free at the positive wire, and hydrogen at the negative, in each half-revolution ; but as the positive and negative cur- rents in each half-revolution are in opposite directions, each 9 polar wire becomes alternately positive and negative, and the oxygen in the second half-revolution appears at the same wire as the hydrogen in the first, and the hydrogen in the second at the same wire with the oxygen in the first ; these imme- diately re-combine, and thus the chemical effect of the first half- Why may these be regarded as in effect hut two? Explain why the poles are alter- nately affected with opposite kinds of electricity. What are the physiological effects? the effects upon the maguet? the chemical effects? PAGE S 483 revolution is neutralized by that of the second. In order to obviate this difficulty, it is necessary to turn up one of the arms of k t so that it will not touch the mercury, and thus suppress the current in every alternate half revolution. By this ar- rangement, only two momentary electrical currents are produced in every revolution ; but as they are both in the same direc- tion, and of the same kind, the poles are not alternately rev- ersed. The power of the machine is thus reduced one-half; but thus arranged, this current of induced electricity may be used to produce chemical decomposition, in the same man- ner as the current from an ordinary galvanic battery. 468. Pace's Magneto-Electric Machine. The mercurial cups in the instrument just described alternately receive a cur- rent of positive and negative electricity, but by the use of a pole-changer, their connection with the wires which terminate the coils may be changed twice in every revolution, and thus the electricity of each cup be made constantly the same, and a continuous flow of electricity of the same kind maintained from. each cup, that may be u.sed for any of the purposes for which the electrical current of the battery is generally employed. This object is best accomplished in Page's magneto-electric rna- Page's Magneto-Electric Machine. chine, Fly. 247 : M, M, are two powerful permanent magnets, arranged one above the other in such a manner that the north pole of the upper magnet is above the south pole of the lower, Why must the current in every alternate half -re volution be suppressed? What effect has this upon the power of the machine? 468. Describe Page's machine. How are the coils mounted ? 48 1 MAGNETO-ELECTRIC and the south pole of the upper ahove the north pole of the lower : A, A, are two armatures, each wound with a coil of fine wire in opposite directions, and mounted vertically between the magnets, so that their iron cores are exposed at both extrem- ities simultaneously to the inductive influence of the opposite poles of both magnets, instead of one extremity only, as in Saxton's machine, and become much more powerfully magnet- ized : these coils have their extremities connected with oppo- site sides of the pole-changer attached to the vertical shaft, on Avhich the coils are made to revolve by the wheel w ; P, N, are binding cups, filled with mercury, insulated from the magnets and each other, and connected with the pole-changer by wires which press tightly upon its surface. At every half-revolution the direction of the electrical current flowing through the coils is changed, and those extremities of the coils which, at the pre- ceding half-revolution, discharged a positive current, now dis- charge a negative one; at the instant that this change takes place, their connection with the cups is changed, and the ends which formerly gave off positive electricity, but now negative, become connected with the cup which then received the negative current, and the ends which formerly gave off negative electri- city, but now positive, become connected with the cup which rhen received the positive current ; consequently, each cup receives, and gives off, the same kind of electricity in the second half- revolution, as in the first. This change of the ends of the coils is effected by the pole changer, represented in Fig. 248 : s, rep- resents a cross sec- Fig. 248. tion of the vertical shaft on which the armatures revolve; A and B, are two pieces of brass, which encircle the shaft, but are sep- arated from it by some non-conduct- ing material; they are also insulated from each other by the bits of ivory, i, i; the wires which begin the coils are firmly fastened to A, and those which terminate them, to B : P and N represent wires connected How is the electricity of each cup kept constantly the same? Describe the Pole- changer. , MACHINE. 485 with the corresponding mercury cups, pressed tightly agamst the brass pieces, A and B. As the shaft revolves, A and B revolve with it and the coils ; the instant that the half-revo- lution is teiminated, the direction of the current reversed, and A begins to discharge negative electricity, instead of positive, the connection of A, with the positive wire and cup p, ceases, in consequence of the revolution, and is established with the negative wire and cup N ; at the same instant, B is ceasing to discharge negative electricity, and beginning to discharge positive, and its connection with the negative wire N is broken, and established with the positive wire P. By this simple ar- rangement, the two cups, P and N, are made to di-charge inter- mittent momentary currents of the same kind of electric ty, which approach more nearly a continuous flow, as the revolu- tion of the coils becomes more rapid, and by combining several of these machines whose armatures are so arranged that each shall in turn become mngiietized just before the preceding one has en- tirely lost its magnetism, magneto-electric machines have been constructed by which a continuous current in a uniform direction can be steadily maintained. The break required, p. 406, for giv- ing severe shocks is made by a wire pressing upon a toothed wheel, Fig. 247. This is removed when the instrument is used for chemical decomposition. See Expts., 160, 170, p. 541. 469. Magneto-lSlcctricity used in the Arts, in place of Voltaic Electricity, especially for the illumination of Lig-ht- houses. As the electrical current induced by magnetism possesses all the decomposing, heating and physiological pow- ers of the electricity of the battery, and is much more man- ageable, because produced by a definite amount of motion, it is often substituted for the electricity of the battery, in electro- plating. A single Saxton's machine, if kept in continuous revolution, will precipitate from 90 to 120 ounces of silver per week, from its solutions, and machines have been constructed by which 2J ounces of silver per hour, have .been deposited upon articles properly prepared. They are employed with great advantage by physicians, for the administration of elec- tricity to their patients, on account of the facility with which the rapidity of the shocks may be regulated by the motion of the wheel. They are also sometimes made use of for telegraphic purpo ;es, where an occasional message only is to be sent, as in the case of the fire-alarm of cities for transmitting the alarm fro.n the central office to every district of the city. 4^9. What apnli^ations have been made of Magneto-Electric machines? What results have bee.i attained in electro-plating? in Light-house illumiaation? 486 MAGNETO-ELECTRICITY APPLIED TO , These machines have also been employed for the production of a permanent electric light between two pieces of gas-coke, for Light-house illumination ; the light can be maintained with- out interruption, so long as the magnetic armatures are kept in rotation, and the charcoal remains unconsumed. Many attempts have been made to use the intense light produced by the carbon poles of a powerful Galvanic battery tor the same purpose. When these poles, as has been shown, 354, after having been brought into contact, are slightly separated, even in a vacuum, a light of extraordinary brilliancy is produced : Despretz has calculated that the light emitted by ninety-two of Bunsen's elements, arranged in two series of forty-six each, is equal to that of 1,144 candles, and is to the light of the sun as 1 to 2 ; and the light emitted by two hundred and fifty element?, in a grand experiment made by Profs. Cooke ai d Rogers, in the cupola of the State House, Boston, was calculated to be equal to that of ten thousand candles. Notwithstanding the intensity of this light, from the difficulty of maintaining a perfectly con- stant action in the battery, it is too irregular to admit of suc- cessful use for the illumination of Light-houses, and although tried under every conceivable circumstance, it has thus far proved, for these purposes, a complete failure. In the mag- neto-electric machine, in which the current is produced by a perfectly regular mechanical motion, much greater success has been attained. A machine for this purpose was first con- structed by Nollet, at Brussels, in 1850, and was afterwards improved by Van Malderen. .This machine is represented in Fig. 249. It consists of a cast iron frame, 5| feet high, on the outside of which eight series of five powerful horse-shoe mag- nets, A, A, A, are arranged on wooden cross-pieces. Upon a hori- zontal iron axis extending from one end to the other of the frame four bronze wheels are fastened, carrying 1C coils each, wound with 138 yards of insulated copper wire. These coils are made to revolve in front of the poles of the permanent magnets by an endless band, which receives its motion from a steam engine not seen in the Fig. To obtain the greatest de- gree of light, the most suitable velocity is 235 revolutions per minute. By this rapid revolution, magneto-electric currents of high intensity are induced, which, by the two binding screws a and 6, are conducted by means of long copper wires, to two carbon points attached to the sockets of one of Duboscq's elec- What advantage has this inodc of illumination over the Galvanic Battery? THE ILLUMINATION OF LIGHT-HOUSES. 487 i Fig. 249. The Illumination of Light-houses. trie lamps, 356, as shown in the Fig., mounted upon the top of the Light-hou-e Tower. In this machine, the current in each wire is not always in the same direction ; each carbon is alternately positive and negative, and they are consumed with ' Describe the machine of Nollet and Van Malderen. 488 HOLMES* ' nearly equal rapidity : for the production of the electric light, it is not necessary that the current should be uniformly in the same direction ; when used for electro-metallurgy, however, this is absolutely requisite. A machine of four wheels gives a light equal to 1 50 Carcel lamps ; a machine of six wheels, a light equal to 200 Carcel Inrrm^. 470. Holmes' Magneto-Electric Machine for use in Light- houses. Mr. Holmes has succeeded, by the use of a powerful magneto-electric machine, in producing a light of great power and intensity, for use in Light-houses. The general arrange- ment of the machine is the same as in that which has just been described. It consists of 48 pairs of permanent compound bar-magnets, arranged in six parallel planes, so as to form a large compound wheel, between which the armatures, 160 in number, are arranged in five sets, the tota! amount of wire with which they are wound being about half a mile in* length. The wires are insulated by cotton, and are so arranged as to maintain a continuous current in the same direction, vary- ing from a maximum to exactly one-half the amount of the maximum, in rapid succession. To facilitate the change in the poles, the soft iron cores of the coils are not solid pieces of iron, but are tubes, single, double or treble, as it is found by experi- ment that the same weight of iron, when divided in this man- ner, loses or takes magnetism in much less time than when in a solid form. The steel bars weigh about one ton, and the wheel is made to revolve by a steam engine of one or two horse-power, at the rate of 150 to 250 times per minute. There is a limit to the velocity to be employed when the maximum of electricity is required. This light was for several months in successful operation at the South Foreland Lrght-house, on the English Channel, and afterwards at Dungene s, the actual ex- pense of fuel in working the steam engine, being about the same as that of the oil formerly employed, and the light equal, pho- tometrically, to 14 of Fresnel's first-class Light-house lamps. The same light is also used in the noble Light-houses of La Here, near Havre. This light is nothing but the sparks first ob- tained from the magnet by Mr. Faraday, Fig. 220, made continu- ous by suitable machinery. It is said to possess extraordinary penetrative power for fogs, and that it shines so far at times, that even before it has arisen above the horizon, twenty -five miles off, it can be seen. This is jusjly regarded as one of the most Describe Holmes' machine. What is the Telocity of revolution ? In what Light- housed has it been employed ? How far can it be seen ? MACHINE. 489 interesting scientific applications of modern times, and with the additional improvements which are steadily making, will no doubt in time be adopted in all the most important Light- houses throughout the world. On the whole, however, up to this time, the preponderance of opinion is against the general introduction of magneto-electric machines into Light-hou-es, on account of their liability to get out of order, and the difficulty of securing the skilled labor required for their efficient man ige- nrjnt, there being, in the opinion of the Brethren of the Trinity House, the English Light-house Board, no advantages which can compensate for the want of certainty in Light-house illu- mination. In spite of all the care which the importance of the subject has rendered necessary, tli3 Dungeness electric Light entirely failed, or was inefficient, for upwards of 119.^- hours, between Aug. 1863, and (X-t. 1864; and referring to this, th o Brethren of the Trinity Hou^e say that it appears to them to be impossible to obtain entire immunity from such accidents, so long as human nature is subject to infirmity. These fallings off and cessations have frequently rendered it necessary that the ordinary oil Lamp should be re-lighted ; and notwithstand- ing the power of the magneto-electric light, instances have occurred of vessels being stranded near Dungeness. The ex- pense of maintaining an equal light from Colza oil, under the old oil-system, from wax-candles, Bunsen's battery, and the magneto-electric machine, being about the same, the question must be decided upon grounds of convenience and effi iency alone. The expenditure of a Light-house of the first-class is about 400 per annum, the light burning four thousand hours, at an expense of about two shillings per hour. 471. Wilde's Magneto-Electric Machine. A great im- provement has recently been made upon Holmes' machine by the substitution of powerful electro-magnets, in place of perma- nent steel magnets. It consists in the application of the current from a common magneto-electric machine, produced by the revo- lution of coils before the poles of a series of small permanent magnets, to the formation of a powerful electro -magnet. This is done by causing the current generated by the revolution of the coils to circulate through wires wound in the ordinary manner around a piece of soft iron, so as to convert it into a powerful horse-shoe eJectro-mngnet. This electro-magnet possesses much more power than the original permanent magnets, on account What are the objections to their u.e ? What is the comparative expense of the differ- ent modes of Ligiit-iiouse illumination ? ill. State the principle of Wilde's machine. 490 WILDE'S - of the intensity of the induced current, produced by the revo- lution of the first pair of coils. In front of the poles of the . electro-magnet thus formed, a second pair of coils is made to revolve with great rapidity, and a second induced current of still greater intensity than the first is obtained. This second induced current is then carried around a second horse-shoe of soft iron and a second electro-magnet formed, of still greater power than the first. In front of the poles of this second electro-magnet, a third pair of coils is made to revolve, and a third induced electrical currrent of still greater power than the preceding is obtained. Each electro-magnet and each in- duced current being more powerful than those which precede them, there is, theoretically, no limit to the power which may l,e thus induced. A small and weak permanent magnet may thus be made to actuate a series of electro-magnets of con- tinually increasing power. Wilde's machine is constructed on this principle, Fig. 250. An armature s A, wound with insu- lated wire, is made to revolve with great rapidity by means of a band from a steam-engine B, in front of the poles of six per- manent magnets, M M, each weighing one pound : from this armature the current is transmitted by the wires p n, through the cups c c, to an inverted electro-magnet E M, in front of whose poles a second armature, carrying coils, is made to re- volve by means of a band B p, from the same steam engine : from this second armature the current which is produced by its revolution is carried by the wires p' ri, to a second electro-mag- net, not seen in the Fig., in front of who e poles a third armature, carrying coils, is made to revolve by means of the same steam-engine, and from these coils the induced current is carried by wires to the carbon points of a Duboscq's electric lamp, as in Fig. 249. The armatures employed in this machine are not wound or mounted in the ordinary manner, but according to the method of Siemen. A cylindrical piece of iron whose opposite sides are cut away, represented in a side view at G, No. 1, Fig. 251, and in an end view at E, is wound from end to end, on each side with covered wire, until the grooves on both sides of the cylinder are completely filled : these longitudinal coils are then firmly bound with bands of brass H H, No. 2, Fig. 251, that they m;iy not be displaced by the centrifugal force of the' revolv- ing cylinder: K is the wheel for the application of the band from thii steam-engine : 1 1 are axles ; L L is the pole-changer. The How is the current induced by the permanent magnet made to create an electro-mag- ne* of much greater power, and this, one of still gi eater power, and this a third ? Is tuere any limit to this process theoretically ? 491 Wilde* s Magneto-Electric Machine. Fig. 251. 1 Sifmen's Armature. T)<- Ladd's Improved Wilde's Machine 498 FIRST IMPROVEMENT. article, to start the electric current in the coils of its revolving armature. Instead of one curved electro -magnet, two straight electro-magnets are placed in a horizontal position and parallel to each other, with poles reversed and having one revolving armature between each set of poles. The electric current pro- duced by the coils of one armature is used to increase the power of the electro-magnets, while that from the coils of the other is carried to the carbon points of the electric lamp and is used for the production of light. The apparatus is represented in Fig. 251*. B B' are the two electro-magnets corresponding with E M in Fig. 250, and placed horizontally. The coils are connected on the right so as to form but one circuit. Two armatures are provided, M and M', one at each end of the electro magnets B B'. The wires p and w, from one armature are carried, as shown in the figure, directly to the electro-magnets and are used to increase their force. The wires ^t/and n' from the other armature lead to the carbon points of the electric light, i, as in Fig. 251, or may be used for producing any of the other effects of the current, such as the decomposition of water, and the like. It is inter- e.sting to observe the continuance of the effects, for some time after the cessation of the revolutions, as is shown by the rise of bubbles of gas from the platinum poles of the decomposing cell in the case of the decomposition of water, Fig. 162. In order to carry off the great heat which is produced, when the revolu- tions are exceedingly rapid, the armatures are punctured and a stream of water is made to circulate through them ; by this arrangement they are kept nearly perfectly cool. 472.* Ladd's Second Improvement. A subsequent im- provement has recently been introduced in the arrangement of the armatures. Instead of being placed, as before, at the oppo- site extremities of two electro-magnets, as in Fig. 251, they are brought together end to end, and fastened very strongly, so as to constitute but one shaft, revolving in one cylindrical aperture, mounted between the poles of one curved electro- magnet, like E M Fig. 250, and driven by one band. The coils wound upon one armature of the shaft are used to actuate the electro-magnet, and increase its power; the coils of the other armature are used to produce the electric light, or for any other external work. The coils upon the two armatures are not placed upon a line with each other, but at right angles, so that one is exerting its utmost power, at the moment when the other is at its dead point ; or they maybe adjusted at any other angle which experience proves to be productive of the most powerful LADD'S 499 effects. By this arrangement the construction of the appara- tus is greatly simplified. The machine is represented in Fig. 252*. It will be observed that the permanent magnets M M have Fig. 252*. LadtPs Second Improvement. been discarded and that there is no primary electro-magnet ac- tuated by a battery, but simply the principal electro-magnet K M of Wilde's machine, and on the top of it, a shaft arranged with a crank and wheels for the purpose of imparting motion to the revolving Siemens' armature placed below. This armature is provided with two entirely distinct sets of coils insulated from each other. The terminal wires of one set, p and n, are car- ried to the electro-magnet, and their current is used to exalt its powfr. The terminal wires of the other set, p r and n f , corres- pond with the terminal wires of Wilde's machine, Fig. 25", and their current is used to produce the electric light, or for any other external work. These two sets of coils operate entirely independent of each other. The instant the armature is made to revolve by turning the crank of the machine, a f -eble cur- rent of electricity is generated in the coils by the slight amount 500 SECOND IMPROVEMENT. of magnetism retained by the electro-magnet since its previous excitation. If it should have entirely lost its magnetism this may be restored for the occasion by applying a powerful per- manent steel magnet to the poles of the electro-magnet, or by touching these poles for a moment by a movable electro-mag- net actuated for the time by a small battery. To this induced magnetism the current from that set of coils which is directly connected with the electro-magnet of the machine immediately adds its magnetic power and at the next revolution of the arma- ture the current of electricity in both coils is greatly iucreased : this in turn adds to the magnetic force of the electro-magnet, which at once reacts again upon the coils, and so the process goes on as the rapidity of revolution increases. There is no limit to the power of the machine but the rapidity with which the armature is made to rotate, and this is entirely dependent upon the amount of mechanical force derived from the steam- engine. The great improvement in this machine is the intro- duction of the second coil upon the Siemens' ai mature, which, although it gives off currents induced by tHe electro-magnet, does not at all detract from the intensity of the original coil ; and when the former is attached to a Duboscq's lamp, it is found to give a light equal to 40 elements of Grove and Bunsen, from the expenditure of an amount of steam engine force equiva- lent to one horse-power. One of these machines, at the Paris Exhibition of 1867, 24 inches in length, 12 in width, and 7 inches high, kept 50 inches of platinum wire 1-1 Oth of an inch in diameter, incandescent, and when a small voltameter was placed in the circuit of the double armature, gave off about 16 cubic inches of gas per minute, and in connection with an electric lamp, emitted a light equal to that of about thirty-five Grove's elements, the driving force being less than one horse-power. These electro-magnetic machines are all extremely interest- ing as illustrations of the theory of the Convertibility of Forces. 473. Points of difference between the electricity of the Electrical Machine and that of the Galvanic Battery. We have already noticed, 351, some of the points of difference between the electricity of the machine and that of the battery, viz : that the electricity of the machine possesses great inten- sity, but limited quantity ; that of the battery, feable intensity, but large quantity, that its influence upon electrometers and electroscopes, is extremely slight, that a Leyden jar can only be charged with difficulty, that when the polar wires are brought 470.* Describe Siemens' and Wheatstone's machines. 471.*-472.* Ladd's machines. THE ELECTRICITY OF THE MACHINE 501 near each oilier only a feeble spark will pass, and on establish- ing a communication between them by means of the hands, pre- viously moistened, a shock is felt, but only for a moment: we have also seen, 415, that its velocity is very much less, prob- ably not exceeding 18,000 miles per second, while the velocity of statical electricity is 288,000 miles per second. On thw other hand, galvanic electricity is developed in much larger quantity than statical, and in a steadily flowing current ; it pos- sesses also much greater heating, chemical and magnetic power, and exerts a peculiar effect upon the nervous system of animals. Notwithstanding these points of difference, it was believed from the earliest period in the history of galvanism, that it could bi> identified with statical electricity, and many attempts were made to establish the most conclusive test of identity, viz : the projec- tion of the electric spark between the poles before actual c in- tact, corresponding with the escape of vivid sparks from the h ghly excited prime conductor of an electrical machine. The electricity which is excited by rubbing a glass tube with a silk handkerchief, will pass without difficulty across half an inch of space, and give a bright and noisy spark, while the electri- cal current of a battery of several hundred pairs, will hardly force a passage through a stratum of air too thin to be appre- ciated, or produce a spark bright enough to be perceptib'e. Sir H. Davy asserted that 2,000 pairs of Wollaston plates, the most perfect form of the battery in his day, gave a spark l-20th to l-40th of an inch in air, and ^ an inch in vacua. Mr. Chil- dren stated that 1,250 pairs gave sparks through l-50th of an inch. Daniell asserted that he had often seen sparks playing between the cells of his battery when they were approximated too much. Faraday stated that a spark would pass before contact even with a single pair. On the the other hand, many experi- menters were inclined to deny the passage of any electrical spark at all before contact, even with the most powerful batteries. Jacoby found that the current from 12 pairs of plates in the most active operation, would not pass through l-20,000th of an inch. Gassiot asserted that a battery of loO pairs would not project a spark through 1 -5,000th of an inch before contact, though it would give a minute but not brilliant spark on sepa- rating the poles, if tipped with charcoal: also, that a water bat- tery of 1,024 pairs, would not project a spark through l-5,00()ih VThat is the influence of galvanic electricity upon electrometers and the T.eydenjar? What is the power of giving shocks an'i sparks? What is its velocity? How was the identity of the two attempted to be proved? Give the statements of Davy, Children, Daniell, Faraday, Jacoby and Gassiot, in regard to the projection of sparks by the battery. 502 AND BATTERY COMPARED. of an inch, although a Leyden battery could be charged by it, so as to project a s t jark through 6-5,OOOths of an inch. Walker proved that a constant battery of 99 cells would not project the spark through the thinnest measurable stratum of air. But it was finally determined by Crosse, in 1840, that a water-battery of 1,200 pairs, would give a constant small stream of sparks between the polar wires l-100th of an inch apart, before contact ; and Gassiot, suspecting that his previous battery series had not been sufficiently extended or insulated, constructed a water- battery of 3,000 pairs, and obtained sparks freely from its pole-. By these experiments it came to.be definitely settled that the galvanic battery would project a spark like a common electrical machine, and an actual identity was established . between gal- vanic and statical electricity. 471. Points of resemblance between the Electricity of the Electrical machine and the secondary currents of Electri- city induced by the primary current of the Battery and by Mag-nets. On the other hand, the secondary current of ele - tricity induced by the primary current of the battery, on mak- ing and breaking connection, not being derived from the bat- tery or from the primary current, but being simply the natural electricity of the secondary wire, disturbed and brought into activity by inductive influence, might be expected to exhibit a very close resemblance to that of the electrical machine, which is also nothing but the natural electricity of the glass plate of the machine thrown into a state of disturbance by means of friction. Thus, by the magneto-electric machine, the gold e:ive$ of the electroscope may be made to diverge directly without the aid of a condenser, and a Leyden jar may be charged at every touch, provided one terminal wire of the coll is in connection with the outer coating of the jar, and the other carried to the knob by an insulated handle, the knob being connected with the inner coating by a wire instead of a chain : the sparks which are emitted are of the most vivid character, of great power, and violence, and often times extend through a space of several inches, surpassing all electrical machines except those of the largest size : the shocks are al o extremely violent, and frequently danfrerous, and the noise almost deafening. 475. The quantity of Electricity produced by the Battery immense, and its magnetic effect far superior to that of the Machine. Notwithstanding the extremely feeble intensity 'of Give the experiment of Crosse, and the second experiment of Gassiot. What present opinion in regard to their identity ? 474. State the points of resemblance be- tween the electricity of the machine aud that of the secondary current induced by the primary current and by magnets. THE QUANTITY OF ELECTRICITY 503 the electricity of the battery, its quantity is enormous. Mr. Faraday estimated the quantity of electricity furnished by the decomposit'on of a single grain of water, as equal to eight hun- dred thousand discharges of a battery of Leyden jars exposing thirty-five hundred square inches of surface, and charged by thirty turns of a powerful electrical machine. The experiment was performed in the following manner. Two wires, one of zinc and one of platinum, each l-18th of an inch in diameter, were immersed during 4-30ths of a second, to the depth of 5-8ths of an inch, and 5-lCths of an inch apart, in acidulated water prepared by adding a single drop of sulphuric- acid to four ounces of water. The current produced by this exceed- ingly small battery, effected as great a de via! ion of the galvan- ometer needle, and decomposed the same amount of iodide of potassium, as thirty turns of a powerful plate electrical-machine: twenty-eight turns of the machine produced an effect, percepti- bly less than that produced by the two wires. The quantity of acidulated water decomposed within the battery in order to furnish this vast amount of electricity, was so small as to be incapable of measurement, and entirely inappreciable; but the electricity produced by it, if concentrated so as to be discharged in a single flash during a minute fraction of a second, from a Leyden battery having 3,500 square inches of surface, would kill a cat or a rat, and be intolerable to a man. From this ex- periment Mr. Faraday made the calculation that the electricity produced by the decomposition of a single grain of water in the battery by the action of the zinc plate, is equal to that fur- nished by eight hundred thousand discharges of an electrical machine, each equal to the one just described : or that the de- composition of one grain of water evolves a quantity of elec- tricity sufficient to charge a surface of 400 acres, an amount hardly exceeded in the most violent storms. It has been calculated, that if this amount of electricity, furnished by one grain of water, were spread upon a cloud two-thirds of a mile distant from the earth, it would exert an attractive force upon the earth beneath it, of 1,664 tons ! and that if the atoms of oxygen in this grain of water were attached to one thread l-25th of an inch long, and those of h}d:ogen to another, th0 tons! yet this amount of electricity is evolved, withou' 475. Describe Mr. Faraday's experiments upon the quantity of electricity producf ' by the buttery. Give his conclusion in regird to the amount set free in the derompo.',. tion of -i single grain of water. Describe the difference betweeu the electricity of t'- 1 \ machine and that of the battery in regard to magnetic effect. 504 PRODUCED BY THE BATTERY IMMENSE. noise, shock, or visible appearance of flame, in every case when rather less than six cubic inches of hydrogen and three cubic inches of oxygen, are set free by the action of four grains of zinc upon one grain of water. This, if concentrated into a single discharge, would be equal to a very vivid flash of lightning, whence it follows that the electricity set free in the decomposition of one grain of water by the four grains of zinc which are required, yields an amount of electricity equal to that of a powerful thunder-storm. Such is the differ- ence between the electricity of the battery and the e^ctricity of the machine, in regard to quantity. Their difference in regard to magnetic effect is equally remarkable. A piece of copper and a piece of zinc, the size of a cent, will produce a magnetic -effect far superior to that exerted by the most pow- erful discharge of the electricity of the machine ever obtained. In experiments made upon the Atlantic cable, an electric cur- rent was sent through one thousand miles of it submerged in the water and a sufficient magnetic effect exerted upon the reflecting galvanometer, 418, to communicate a message, by a battery consisting of a silver wire and a zinc wire of the size of a pin, excited by a drop of acid supported between them by capillary action. 475. The action of Electricity and Magnetism on Lig-ht. Electricity, whether produced by the machine, by the battery, or by magnetism, has not only the power of produc'ng light, but a'so a very singular effect on light after it is produced. Sir H. Davy ascertained, 359, that the light produced by the approach of two poles of a powerful battery, is influenced by the magnet, and is acted upon in the same way as any moveable m3tallic conductor traversed by the galvanic current: it is at- tracted and repelled by the mug- Fig. 253. Fig. 2 r >4. net, and a rotary mot r on imparted manifesting itself by a change in the form of the arc. By holding the magnet in a certain position, the flame may be made to re- volve, accompanied by a louJ sound ; and the form of the arc may even become broken by too great an attraction or repul ion. The arc of Voltaic. Light. Fig. 253 represents the ordinary 473 State the effect of the magnet on the electric light. How has it been shown that light is strongly diamaguetic J THE EFFECT OF MAGNETISM! 5C5 Fig. 255. form of the voltaic arc between two cylinders of plumbago, and Fig. 254 the curved form which it exhibits under the in- fluence of a magnetic pole. It has also been ascertained that light is strongly dia-magnetic, and assumes an equatorial position in the magnetic field. Bancalari observed that the name of a candle placed between the poles of an electro-magnet, was re- pelled into a position at right angles to a line joining the poles, Fig. 255, as if blown by a current of air. M. Quet obtained a similar result by submitting the voltaic arc to the influence of powerful electro-magnetic poles, Fig. 256. It has been shown that the auroral light produced by Ruhmkorff's coil in the electric egg, Fig. 234, is made to revolve around an electro-magnet as eoon as the connection is formed with the battery, tnat the stratified bands and luminous discharges of Geissler's tubes, 461, are powerfully affected by the magnet, and that the light from the negative pole is specially affected by the magnetic force. Finally Mr. Faraday has as< ertained that a ray of light may be electrified and the electric forces illuminated., He observed that if a ray of polarized light were transmitted through a piece of glass placed between the poles of a powerful electro-magnet, on the line joining the two poles, on actuating the electro-mngnet by connection with the battery, the ray of polarized light experienced a rotation, to the right or the left, according to the direction of the current. A polarized ray of light is one which by reflection, or by refraction through certain substances, has acquired cer- tain peculiar proper! ies different from those of ordinary light, which are summed up in the term polarization. Thus, when a ray of light falls upon a glass mirror at an angle The effect of a powerful El'c'ro- Magnet on the flame of a Candle. Fig. 256. The (ffert of Magnft- jsm on the Voltaic Light. What is the effect of the magnet on the voltaic arc? on the aureraj light of Ruhrn* korff's coil and Geissler's tubes? What is the effect of Maguetisru on polarized Light? "What is polarized Light ? 506 ON LIGHT. of 35 25', it acquires the singular property of incapability of reflection from a second mirror of glass at the same angle, if the plane of incidence of the second mirror be perpendic- ular to the plane of incidence of the first : in other words, the ray becomes extinguished; it is partially reflected and re-appears, for every other inclination of the two planes, and the intensity of the ray reflected from the second mirror in- creases as the angle of the two planes of reflection diminishes. If, at the moment of extinction, a thin plate of quartz crystal, whose faces are perpendicular to its axis, be interposed be- tween the two mirrors, the extinguished ray re-appears upon the second mirror, and in order to re-extinguish it the quartz must be turned by a certain angle to the right or the left. The quartz is said to exercise thus a rotary power, and to deviate the plane of polarization to the right or to the left, according to the direction in which it must be turned in order to re-ex- tinguish the reflected ray. Several other substances besides quartz, such as oil of turpentine, solution of sugar, &c., possess the power of rotating the plane of polarization. The apparatus far showing that a similar rotating power is possessed by mag- netism, is represented in Fig. 257. It consists of two very Fig, 257. The effect of Magnetism on Polarized Light, What is the effect of quartz and some oth^r substances upon the extinguished ray? Describe the apparatus, Fig. 2o7. by which it is shown that magnetism possesses a simi- lar power of deviating a polarized ray of light. THE PROGRESS OF DISCOVERY 507 powerful electro-magnets, M and N, mounted horizontally on two iron supports, o, o', which can be moved on a support K, The current from 10 or 11 Bunsen's cells, is transmitted by the wire A, to the commutator H, by which it may be sent in either direction through the coil M, thence by the wire g to the coil N, and then back again by the wire , to the commutator H, fina-Iy emerging at B. The two cylinders of soft iron on which the coils M and N are wound, are perforated through their entire length by a cylindrical hole so as to allow a ray of light to pass com- pletely through them both. At b and a, there are two of Nicol's prisms, each consisting of sections of rhombohedral crystals of Iceland spar, which have been cut diagonally, and then re-united by Canada balsam. These prisms serve instead of the two mir- rors spoken of a' ove, and exert a similar polarizing effect upon a ray of light. When the lamp is placed opposite b, and the eye at a, the ray of light is completely extinguished. If at this moment there be placed at c, a plate of ordinary or flint glass with parallel faces, the ray of light is still extinguished to the eye at , so !ongas the electro-magnets remain unexcited, but the in- stant the current begins to flow and the electro-magnets become excited, the ray of light will reappear and cease to be extin- guished by the prism a, and to extinguish it again it will be necessary to turn the index attached to a, to the right or le t through a certain angle. If the current be broken the light re- appears ; if the current be reversed, and the poles of the electro- magnets changed, the direction in which the index must be turned in order to extinguish the ray, must also be reversed. Ileive it appears that the electric current, or the magnetic power which it generates, possesses the power of rotating the ray of polarized light which pas es through the core of the magnets, or else imparts this power to the piece of glass placed at c, and that this rotating power is to the right or to the left, according to the direction of the electric current, and is acquired and lo t instantaneously, following the connection with the battery. " Iu this experiment," says Mr. Faraday, "we may justly say, that a ray of light is electrified and the electric forces illuminated," The general conclusion is, that the connection between Elec- tricity, MagnetUm, and Light, whether the light emanates from an electrical source, or from ordinary sources, is extremely intimate, and closely connected with the doctrine of the con- vertibility of Forces, What is rhe general conclusion in regard to the connection between Electricity, Mag- netism and Light? 508 IN REGARD TO VOLTA-ELE-CTRIC 477. Progress of discovery in the induction of Electricity by the Galvanic current, and the construction of Induction Coils and Mag-neto-Electric Machines. The successive dis- coveries which led to the construction of the powerful Induc- tion Coils and Magneto-Electric machines now in use, are as follows. The primary fact of induction, viz : the induction of a secondary current in the primary wire connecting the poles of a battery, and the increased effect obtained by using a long wire, and especially one coiled into a helix, was discovered by Prof. Henry in 1831. In the same year Mr. Faraday made the discovery of the induction of electricity by the battery cur- rent in a neighboring wire, distinct from it, and forming a closed circuit, whenever the battery circuit is completed or broken ; also, whenever the battery circuit is brought near or removed from the closed secondary current. He also di > covered at the same time, the induction of electricity by a mag- net, whenever brought near or removed from a closed circuit consisting of a great length of wire coiled into a helix ; al o, the induction of electricity in a similar coil by the magnetiza- tion and de-magnetization of an electro-magnet by a battery current, and by the magnetization and de-magnetization of a piece of soft iron by the inductive influence of a permanent magnet brought near and removed from it. In 1833, Dal Negro, an Italian philosopher, discovered that the inductive influence of the current of the primary wire connecting the poles of a battery, was more intense if the wire were wound into a coil surrounding a piece of soft iron. In 1834, Mr. Far- aday made the announcement of the same fact, communicated to him by a young man named William Jenkin, of London, viz : " that if an ordinary wire of short length be used as a medium of communication between the poles of a battery of a single pair of metals, no management will enable the experimenter to obtain an electric shock from this wire ; but if the wire which surrounds an electro-magnet be used, a shock is felt each time the contact with the electromotor is broken, provided the ends of the wire be grasped, one in each hand." This fact Faraday confirmed by his own experiments. In 1836, Dr. Page discov- ered the principle that the intensity of the induced current in the secondary wire might be greatly increased by lengthening the secondary coil and making it many times longer than the pri- 477. Who discovered the fact of induction in the primary wire coiled into a helix? Who discovered the inductive action of the primary wire upon a neighboring wire ? Who discovered the increase of effect produced by winding the primary coil arouad a piece, of soft iron ? What was the discovery made by Jeukiu '! AND MAGNETO-ELECTRIC INDUCTIOi.. 509 "v nary coil ; constructed his compound-coil and spark-arresting circuit-breaker, and, in 1838, discovered the advantage of mak- ing use of a number of soft iron wires in place of a bar of solid iron in the axis of the inner coil. In 1853, Fizeau discovered the peculiar effect of the condenser, or Leyden jar, in absorbing the extra-current and increasing the intensity of the induced current in the secondary coil. In 1857, Ritchie invented his improved mode of winding and insulating the secondary coil and breaking the circuit, by which the length of the spark was increased to fifteen inches. And finally, in 1860, by adopting this improved mode of winding, and by greatly lengthening the secondary coil, Ruhmkorff succeeded in bringing his induc- tion coil to its present state of perfection. In the development of Magneto-Electric machines, the origi- nal discovery of the induction of electricity by the magnet, and the production of a current in a wire wound upon soft iron, by the approach and removal of a strong permanent magnet, was made by Mr. Faraday in 1831. In 1832, Pixii constructed his machine, in which a magnet was made to revolve in front of fixed coils. In 1833, Saxton constructed his improved ma- chine, in which the magnets were fixed, and the coils made to revolve ; and in 1 833, Page made still further improvements by increasing the number of the magnets and inducing magnet- ism at both extremities of the iron cores within the coils, and invented his pole-changer, by which each pole always received the same kind of electricity, and one-half the electric current previously lost, was saved. In 1861, Holmes invented thfj combination of magneto-electric machines, which resulted in the production of the permanent magneto electric light, and its introduction for Light-house illumination. This was followed by Wilde's machine in 1866, and by Ladd's in 1867, by which the Magneto-Electric machine has been advanced to its most perfect state, and brought to supersede the light of the sun for photographic pictures. All these wonderful inventions and their applications, directly connected with fome of the greatest improvements in modern civilization, derive their origin from the discovery by Mr. Faraday, in 1831, of the induction of elec- tricity by magnetism, and the production of the electric spark by a fixed magnet ; and therefore, with justice might he say, in the latter part of his life, in speaking of the attempts by Mr. Who discovered the advantage of lengthening the secondary coil? Who first made use of the Condenser? What was Ritchie's improvement? Ruhmkorff ; s? Trace the order of progression in the construction of Magneto-Electric Machines. Jo whose dis- covery is the Magneto-electric light of Light-houses strictly due? 510 THERMO-ELECTRICITY. Holmes at introducing the magneto-electric light into the Light- house at the South Foreland, a subject in which he was much interested, " I will not tell you that the problem of employing the magneto-electric spark for Light-house illumination, is quite solved yet, although I desire it should be established most earne ?tly, for I regard this magnetic spark as one of my own offspring." V2. Thermo-Blectricity. 478. Heat producss Electricity. We have seen that Elec- tricity pro luces Heat : it is found that the reverse is also true, arid that Heat under certain circum tances produces Electricity. If metallic bars of unequal conducting power for heat be soldered together at one extremity, and heat applied at the point of junction, the other extremity of the bars being con- ne^tel wiih the galvanometer, an electric current will be at once produced, flowing irom the hotter to the colder metal. Tiius, in Fig. 25,8, let m n, be a bar of copper, whose ends are bent down Fig- 258. and soldered to a plate of bismuth, p o, and let a mag- netic needle be mounted upon a pivot in the space between the plates, and the apparatus be pLicerl in the magnetic me- ridian ; on applying- the heat of a lamp at o, the needle will be at once detieL-ted in such a mann T as to show the passage of a current of elec- tricity from n to m, in the direction indicated by the arrow. If instead of applying heat at 0, a piece of ica be placed at that point, or cotton-wool moistened with ether, while the juuc- Electricity produced by Heat. 478 Prove that Heat produces Electricity. Describe F/ 6 -. 258- THE THERMO-ELECTRIC 511 tion at m retains its natural temperature, there will be a cur- rent in the opposite direction, from m towards n, and the energy of the current will be proportioned to the difference of temperature between the two junctions. The current is always from the hotter to the colder metal : it has been found that the currents are produced equally well in vacua and in hydrogen, and therefore are not due to chemical action. The true cause is the unequal propagation of heat from the heated junction. Any obstruction to the equal distribution of heat in a metallic conductor, generates a current of electricity, i.i t'.ie same way that any obstruction to the flow of the electric current in a metallic wire produces a rise of temperature. T>vo metals are not necessary to the evolution of the cur- rent: any disturbance of the molecular arrangement so a> to interfere with the equal propagation of the heat from the hot to the cold portions of a bar composed of a single metal, is sufficient to produce an electrical current. Thus a straight platinu:n wire stretched between the binding screws of a g ilvanometer, may be heated at any point without de- veloping the slightest current in the instrument : but if the platinum wire be twisted into a loop so that its molecular ar- rangement is slightly altered at this point, and heat be applied close to the loop and to the right of it, a current will circulate through the galvanometer from right to left, owing to the un- equal conduction of the heat. These facts were ascertained by Seebeck at Berlin, in 1821, and are of great interest as show- ing the intimate connection between Heat and Electricity. It may be stated in general that when two metals, of unequal con- ducting power for heat, are connected in any way so as to form a closed circuit, an electrical current is established flowing from the hotter to the colder, whenever a different temperature is produced between them, and the current is maintained as long as any difference of temperature continues. The metal from which the current proceeds is exactly analogous in situation to the zinc plate in the battery ; the metal to which the current proceeds is analogous to the platinum plate. The different metals do not all possess this power when associated ; and the direc- tion of the current depends upon the rnetals which compose the circu't. When bars of a itimo ly and bismuth are soldered to- gether and heated at th;i junction, the current flows from the Does the cat rent flow from the hot to the cold metal or the reverse? What is the effect if there be any obstruction to th<> equal proposition of hent in a metall'o con- d'lot/n-? VFhat always takes place when two metal* of unequal conducting power are connected so as to form a closed circuit and heated ? 512 BATTERY. cold end of the bismuth to the cold end of the antimony, as represented in Fig. 258. The following series represents the thermo-electric order of the metals, each metal being positive in reference to the metals which come after it, Bismuth, Mer- cury, Lead, Tin, Platinum, Copper, Silver, Zinc, Iron, Antimony. When heated together, the current proceeds from the cold extremities of those which are first on the list to the cold ex- tremities of those which are last. The thermo-electric order is very different from the voltaic order. Other substances besides the metals will also produce electrical currents when soldered together and heated. Gas-carbon may be used in connection with German-silver, with silver, and with iron, and it has even been found that the point of a heated cone of porcelain, if brought into contact with a cold cylinder of the same material, will gen- erate a thermo-electric current passing from the hot cone to the cold cylinder, each being connected with the galvanometer by cotton soaked in some conducting liquid. When the process is reversed, and a weak galvanic current is transmitted through a thermo-electric series, heat i* produced if the current be sent in the same direction as the thermo-elec- tric current, and cold if in the reverse direction. 479. The Thermo-electric Battery. By connecting the col< I bismuth end of a thermo-electric pair- Fig. 259. composed of antimony and bismuth, with the cold antimony end of a second pair, as shown in Fig. 259, the bismuth being repre- Tiiermo-dectric Pile, sented by the white bar, and the antimony by the black, and so through a long series, a battery may be constructed, the power of which increases with every additional pair. While the ends of the pairs on one side must be heated, those on the other side must be kept cool, in order to obtain the most pow- erful effects. When arranged as in Fig. 260, the extremities of the se- ries being connected with a galvan- ometer by means of wires, upon the application of heat at the upper ends, the needle is powerfully deflected, and iodide of potassium and acidulated water may be decomposed. The legs of a fro" 1 may conyulsions even be thrown into the curren t proceed, NOBILl's THERMO-ELECTRIC BATTERY. 513 ing from a single pair. If the lower ends of the pairs be heated while the upper are kept cool, the direction of the current will be reversed. The intensity of the current is feeble, but in quantity it closely resembles a weak galvanic circuit: its chief effect is therefore magnetic, and a battery composed of sixty pairs of bismuth and antimony bars, three inches long, three -fourths of an inch wide, and one-fourth of an inch thick, whose extremities on one sida are heated by a hot plate of iron, and on the other cooled by immersion in snow mixed with half its weight of salt, will produce an electro- magnetic current sufficient to raise a weight of fifty pounds. 430. The Thermo-electric Battery of Nobili. The first thermo-electric battery was constructed by Oersted and Fourier, but Nobili was the inventor of the arrangement now generally used ; he united bars of bismuth and antimony in such a way as to form a series of five pairs, the bar of bismuth b, being con- nected with the lower an- Fig. 262. Fig. 261. timony bar of a second similar series placed ver- a + tically by the side of the g-^^ fi rst? Ffg m 261, then the &" ." ;'' ^'^-g last bismuth of this series ;';/ r ' ' "'ZjJ with the first antimony of ~~ ZZZI~> a third, and so on for four If'"- vertical series containing 20 couples, the whole se- ries commencing with a NobiWs Thermo-electric Battery. bar of bismuth and end- ing with one of antimony. The pairs were insulated by means of bands of paper covered with varnish, and then enclosed in a brass case, in such a manner that the junctions of the bars appeared at the opposite ends of the case, Fig. 262. Two binding screws, x and y, insu- lated by ivory and communicating, the one with the first anti- mony, and the other with the last bismuth bnr, constitute the poles of the battery, and admit of the attachment of wires connecting with a galvanometer, as represented in Pi?. 263. When thus connected, the slightest difference of temperature between the two ends of the battery is sufficient to excite a What is the thermo-electric order of the metals? Will any but metillic substances answer ? What is the effect of transmitting an electric current through a thermo-elec- tric series? 479. Describe the thermo el ctric battery. What are its effects? Wliat is its magnetic power? 480. Describe the therino electric battery of Nobili. 514 MEL L ONI* S TIIEllMO MULTIPLIER. current of electric- ity, and produce a very sensible de- flection of the nee- dle of the galvan- ometer. 481. TheTher- mo-IVXurtiplicr of melloni. Nobili's battery thus ar- ranged and con- nected with a galvanometer, is the instrument with which Mello- ni made his cele- brated researches in regard to the transmission of heat through screens, 88, and proved the existence of a calorific. tint for heat in thin plates similar to the colorifc tint for light. It was named by him the Thermo-Multiplier, Fig. 2G3. The Fig. 264. Tke Tiitrnw-eUctric Multiplier for measuring heat. MeUoni's apparatus for measuring thf transmission of radiant heat by the Thermo- Multiplier. arrangement of his apparatus was as follows, Fig. 2G4. Upon a FARMER'S THERMO-ELECTRIC 515 tablet of wood, a brass rule was mounted, about a yard in length, and carefully graduated. This rule supported at varying d s- tances the different pieces of which the apparatus was composed ; on a stand a, was mounted the locatelli lamp, or other source of heat ; then the screens F and E ; then a second support c, on which were placed the substances whose diathermic power was to be determined; and finally the thermo-electric pile m, who^e poles A and B, were connected with the galvanometer D, by short and thick wires. The diathermic power of the substances in ques- tion was determined by the degree of deflection in the galvan- ometer. A thermo-electric pile, with galvanometer attached, wa? also the instrument used by Tyndall in his experiments upon the absorption and transmission of radiant heat by gases, described in his work entitled, ''Heat a Mode of Motion'' and it constitutes the most delicate known Fig. 265. instrument for measuring slight degrees of heat. The heat of the hand at the distance of several feet, warm air breathed from the mouth, or even the heat produced by the impinging of compressed air upon one end of the battery, the temperature of insects, Fig. 265, and, on the other hand, The temperate ejects measured e V ll 7 sli g ht depressions of tem- by the Tker mo-Multiplier, perature at the OppO-lte CJld of the battery, all produce a re- markable deflection of the needle, and are capable of being measured by it. 482. Farmer's Thermo-Electric Battery. A thermo-elec- tric battery has recently been constructed by Mr. Farmer, the inventor of the Electric fire-alarm, 430, which may be substituted with great advantage for the. galvanic batteries and magneto- electric machines in common use. A series of pairs of German- silver and bismuth, are arranged with their soldered extremities pointing towards a common centre, in such a manner as to make a perfect circle, 1, Fig. 26t>; the electric current circu- lates from pair to pair, and finally appears at the polar binding screws ; by means of these screws the current may be transmitted to the binding screws of a second series, 2, entirely 4 Q 1. Describe Melloni's Thermo-multiplier. Describe the arrangement O f Melloni'g apparatus for measuring t'.ie transmission of radiant heat. What sligat degrees o/ tem- perature can be uie.i3ureJ. by tais iuitruaieut? 516 BATTERY. Farmer' 's Thermo- Electric Battery. insulated from the first, and pro- ducing a similar current, and thence to a third, finally emerging at the poles. p and n. In order to actuate this bat- tery, it is only necessary to ap- ply heat within the internal cylin- der to which the pairs point. This may be done by means of charcoal, gas, or an alcohol lamp. In Fig. 266, G is a tube connecting with a ga burner, B is the ga^-burner of the battery, c is a deflector to keep the h j at down in the centre. All that is required to put the battery in operation, is to turn on the gas and light the burner B ; it ac- quires its maximum of activity in a few moments, and works con'inuously and constantly as long as it receives heat, pro- ducing a steady and perfectly uniform current of electricity for an indefinite period, without any perceptible variation in strength. It may be employed for any of the purposes for which a common galvanic battery is used, for working the telegraph, precipitating metals from their solutions, exciting electro-magnets, operating fire-alarms, producing the electric light, or actuating Page's or Ruhmkorff's coils for medical use, and is particularly adapted to electrotyping, plating and gilding, because no acids, mercury, or liquids of any kind are required. There is no waste of the metallic pairs, as they re- main as good at the end of the year as when first used. It requires no attention after being first lighted, and will run day and night without any change, as long as heat is applied. It is also very economical, as five or six pounds of coal will evolve as much electricity as one and a half pounds of zinc, five or six pounds of sulphuric acid, and one ounce of mercury. Ten pairs are estimated to be equal to one Smee's cell ; twenty -four pairs to one Daniell's cell, and forty-four to 482. Describe Farmer's Thermo-electric battery. What is required to put this bat- te'-v into operation ? For wliat purposes may it be employed ? Wiiat are its ad vantages ? ANIMAL 517 P one Grove's cell. The cost of working such a ba'tery possessing half the power of a G/ove cell, and five times that of a Daniell, is one-third of a cent per hour with gas, and two cents per hour with an alcohol lamp.. It has been estimated that a light equal to that of 5,000 can:lles, can be produced, By a Grove's battery, at a cost of, per candle, per hour, of 5^ mills. / By Illuminating Gas, 1 u By S:nee's battery, 1 , By the Magneto-electric machine, . . . 0.10 " Also, that from one pound of coal used in the steam-engine to drive the magneto-electric machine, or in the thermo-electric battery, a light equal to that of about 144 candies can be ob- tained : also that the total electrical energy contained in one pound of pure carbon, completely burned into carbonic acid, and its heat used to produce electricity, and through electricity converted into Light, will furnish an amount equal to that of a candle burning 1 year and 5 months ; and that if all the energy in a pound of carbon could be converted into Light by means of the electricity which it is capable of generating, it would be equivalent to the burning of acindle for 12,410 hours. This will give soma idea of th'3 tremendous amount of energy capable of being furnished by the electricity derived from Heat. VIZ. Animal Electricity. 483. Animal Life produces Electricity. The vital prin- ciple of the Animal economy in all animals produces Elec- tricity, and in soni3 animals is capable of generating very powerful electrical currents. The torpedo, a flat fish, found in the Mediterranean, is provided with two electrical organs, situated one on eac;h side of the spine, near the head, and a powerful shock is received on simultaneously touching the back and the belly of the fish at any part; but the strongest shock is obtained immediately over the two organs. The gymnotus, a fresh water fish, abundant in the waters of the Orinoco, has four electrical organs, running from the head to the tail of the animal. So great is the electrical energy State the comparative expeise of producing a light equal to that of 5030 candles from Grove's battery, Smco's, Illuminating Gas, and the Magneto-electric machine. State the total electrical energy contained in one pound of coal. State the jllumiuatiug power of one pouud of Carbon, if converted into light. 518 ELECTRICITY. of the animal that a fish 40 inches in length, has given a shoek which, it has been calculated, is equal to that emitted from a Leyden battery of 15 jars, exposing 3500 square inches of coated surface. The shocks from the gymnotus are sufficient to stun, and even kill, large fish ; and give rise to electric cur- rents of enough power to deflect the galvanometer, mag- netize a needle, decompose iodide of potassium, and even pro- duce sparks. It has been shown, also, that in all living ani- mals an electrical current is perpetually circulating between the interior of the muscles and their external surface, probably due to the vital changes which are continually going on in the organic tissue. In warm-blooded animals, this current ceases in a very few minutes after death ; but in cold-blooded animals, it continues for a much longer period. If five or six frogs be killed by dividing the spinal column just below the head, the lower limbs removed, and the skin stripped from them, the thighs separated from the lower legs at the knee joint, and then cut across transversely, a battery can be constructed from the pieces. Thus, let the lower half of the thighs be placed upon a varnished board, and arranged so that the knee joint of one limb shall be in contact with the transverse section of the next, and a muscular pile can be formed, consisting of ten or twelve pairs ; the terminal pieces should be made to dip i:i*to small cavities, in which distilled water is placed. If the wires of a galvanometer be introduced into these cavities, by means of two thin platinum- plates, a deviation in the needle will be observed ia such a direction as to show the existence of a current passing from the centre, or cut transverse end of the muscle, towards its exterior. This muscular pile acts equally well in highly rarefied air, in carbonic acid gas, and in hydrogen ; in the last gas the needle of the galvanometer, after being moved, remains stationary for several hours. This nullity of the action of the several gases is thought to prove that the oxygen of the air is not necessary, and that the origin of the current is in the muscle itself, and depends rather on the organization of the muscular fibre and the chemical actions going on within its structure. If a prepared frog be placed with its lumbar nerves plunged into one capsule filled with water, and its legs placed in another, th3 circuit being completed through the galvanometer, the ins:ru- ment gives indications of an electrical current passing from the foet towards the head of the animal. The effect is very much 4S3. Can the vital principle of animals produce electricity ? Describe the torpedo. What effaot? are produce i b 7 it ? Is t icre an electrical current circulating in all a:ii- mab ? D3^.?ib3 1 13 fro^ battery. Ho,r is it sho,rn that thz current ia not produced by the action of the air ? THE PHYSIOLOGICAL 519 Fig. 252. increased when several frogs are arranged on an insulated sur- face in the manner shown in Fiy. 252, the spinal cord of each frog touching the legs of the following; every time the circuit is completed, the needle of the galvanometer moves, and the limbs of the frogs contract. It is probable that further inves- tigation will develop a still closer relation between electricity and the vital force of the Animal economy. 484. The Physiological ejects of the Galvanic Current. On the other hand the physiological effects of the galvanic cur- rent upon the animal economy are equally remarkable. The convulsive movements i.i the leg of the frog, noticed by Galvani, led to the invention of the voltaic pile, and the formation of a new scien> e. When the wire from one pole of the battery is put in communication with the nerve of any 1 \\f\fllJ limb of an animal recently killed, Fig. 2.">3, I \ I IM and the wire from the other pole with the outside of the muscles, the limb will 1 e contracted with great violence, the musdes of the face will be made to di play the va- rious emotions and passions of the mind, and many of the vital processes of secretion and digestion will be recommenced, so that there is good reason for supposing a close connec- tion between the galvanic current and the nervous energy by which all the vital func- tions are maintained. By means of a powerful galvanic current, small animals, such as rabbits and hares, which have been suffocated half an hour, have been brought to life. The face of a prisoner, who had been exe- cuted by hanging, exhibited such dreadful muscular contortions when exf'ited by the galvanic current, as to horrify the spectators : the trunk partially raised itself, the Innds were agitated and the arm-< swung wildly, the chest rose and fell as though respira- ti-m had recommenced, and nearly all the vital processes were set in motion ; but the whole effect ceased as soon as the current Battery c tiie legs of Frogs. Describe the arrangement of the frog battery. 484 State the physiological of k'ie curroi*-. What is the effect upon small animals that have been suffocated? Pe- ecribe the effect upon an executed prisoner. 520 EFFECTS OF THE > was withdrawn. If the fingers be moistened and applied to the poles of the battery, a smart shock \rill be obtained, the strength of which will depend upon the number of plates or cells em- ployed ; if two metallic handles be connected with the two poles, and grasped by the moistened hands, the strength of the con- tinued succession of shocks will be greatly increased. The Fig. 253. Tht effect of the Galvanic current on the Animal economy. most severe shocks are given, however, not by the direct cur- rent of the battery, but by the induced currents of Page's and Ruhmkorff s coils, and the various Magneto-electric machines. Shocks of great violence can thus be given, and so firm a mus- cular contraction of the hands produced, that it Avill be impos- sible to relax the grasp. It has also been found that these in- duced currents exert a different effect upon the system, from tlio direct current of the battery, and do not produce the same chem- ical disturbance of the functions of the body. Various instru- ments have been invented for the application of these currents to medical purposes. Of these the most efficient is Page's sep- How can shocks be taken from the battery ? What is the effect of using metallic bandies ? By what instruments can the most severe shocks be obtained ? GALVANIC CURRENT. 521 arable helices 451, with the coils arranged horizontaHy, on ac- count of the facility with which the shocks may be regulated. With this apparatus, there are some peculiarities in the shock depending upon the motion of the battery wire over the rasp : if it is moved slowly, distinct and powerful shocks are expe- rienced ; if the motion be more rapid, the arras are much con- vulsed : and if it be drawn very rapidly, the succession or' shocks becomes intensely painful. The violence of the shocks can be easily regulated by the number of iron wires employed, and by varying the distance to which they are inserted. The power of the shock depends very much upon the extent of the contact surface between the hands and the metallic conductors ; if two wires only are used, and held lightly in the fingers, the effect is much less than when metallic handles are employed especially if the hands are moistened with salt water. Shocks of a peculiar character may be given by placing the polar wires in two ba- sins of water, and then dipping a hand into each basin ; in this ca>e the strongest sensation is experienced when the ends of the fingers only are immersed; if a large surface be exposed the shock will be felt strongly through the arm?. The-e shocks will pass without much diminution of intensity through a circle formed of several persons, although different individuals are very differently affected, the shock which is felt by some only in the fingers or hands, in the case of others extending to the arms and breast. There is a difference in tho strength of the shocks in the two arms ; if the positive handle be held in the right hand and the negative in the left, the left hand and arm will experience the strongest sensations, and be the most con- vulsed. This remarkable difference of inten-ity is believed to be a purely physiological peculiarity, a greater effect being pro- duced by the current, in the arm in which it flows in the same direction as the ramification of the nerves, than in the one in which it flows in an opposite direction. If both wires are put into the same trough at some distance apart, and a finger of each hand be placed in the water in a line between the two wires, a shock will be felt, because the current finds a passage through the body more readily than through the water, which intervenes between the fingers ; but if the fingers be put in at right angles to the line between the wires no shock will be felt : if the conducting power of the water be made better than that How can the violence of the shocks he regulated 1 What is the effect of taking: the shocks through water? Is there any difference in the effect upon the two arms ? How may the effect of the shock from water be increased ? 522 THE VARIOUS SOURCES OF ELECTRICITY. of the body, by dissolving in it a little common salt, little or no shock can be perceived. It -has also been ascertained that in- duced currents of different orders produce different effects upon the body. An induced current of the first order, produces strong muscular contractions, but has little effect upon the sen- sibility of the skin, while an induced current of the second or- der increases the cutaneous sensibility to such a degree, that it often cannot be applied to persons of great nervous susceptibility. 485. The various sources of Electricity, and its Relations to the other two Chemical Agents, Heat and Lig-ht. The study of Static and Galvanic Electricity has shown, that this wonderful agent can be produced by a great variety of sources: by Friction; by Chemical action; by Magnetism; by Heat ; and by Vital action. It has also shown that it is capable of producing, or of being converted into, all the Forces, which act on matter, except Gravity, viz, Motion ; Heat ; Light ; Chemical action ; and Magnetism ; and that it can imitate the effects, if riot actually produce several of the properties of the Vital Force. It is distinguished from the other Forces by producing more intense and powerful effects. The heat which it generates is the most intense heat known ; the light, which it evolves is su- perior to the light of the Sun ; the motion which it causes is infinitely more rapid and prompt than any which can be brought about by the more tardy operation of either Heat or Light : the physiological sensations which it exerts are more decided, and evident than those of the other forces. It is especially re- markable for the extraordinary influence which it exerts over chemical affinity. It is able to break up and destroy some of the mo-t powerful combinations existing in Nature, and has dis- closed the existence of a very large number of the chemical elements known to the chemist. It stands out, therefore, as in some respects superior to the forces of Heat and Light. Con- sequently it is a more prominent and valuable agent for the mod- ification and control of Chemical affinity than either Heat or Light, and is emphatically the chief instrument which the chemist has at command in his investigations into the constitu- tion of matter for the purpose of determining its composition and the nature of the elements which enter into it. What different effects do induced currents of different orders produce? 4S5. Wh"t are the various sources of electricity? How is it distinguished from other forces? "Why more valuable to the Chemist ? 22 THE RELATIONS SUBSISTING 523 VIII. Conclusion of the Chemical Forces. 486. The Relations subsisting- among- the three Chemical Forces, Heat, Lijht and Elasticity. They are convertible, ail probably di3 to ths notion of the molecules of bodies. It is evident fro.n what has been already said, that the three Chemical forces, Heat, Light and Electricity, are not mde- pendent of each other, but very closely related, and mutually convertible. Tans Heat, when accumulated to a sufficient de- gree in bodies, is capable of producing both Light and P^lectric- ity without the intervention of any other force. Lig'.it is capa- ble of producing both Heat and Electricity not directly, but by the intervention of the force of Chemical affinity. Electricity is capable % of producing Heat and Light directly, and by the rapid magnetization and de-magnetization of an iron bar, 398, can also produce both Molecular motion and Heat. These Forces are all capable of being produced by the force of Mechanical mo- tion ; and it is thought by so.ne can always be traced ba -k to their origin, in Motion. If this be so, they are all due to one cause, viz Motion of the molecules of bodies. Thus Heat, it is well known, can be produced by Motion, and every kind of Heat, as we have seen, 238, p. 230, even the Heat of combus- tion, is susceptible of explanation on this principle. Light can also be produced directly by Motion, as is proved by the flash which accompanies the collision between projectiles and the target, 243, p. 216. Electricity can also be produced directly by Motion, as is proved by the operation of the ordinary elec- trical machine and the revolution of colls in front of the poles of a magnet. The derivation of the three Chemical Forces from Motion, and their mutual convertibility are elegantly shown by the magneto-electric machines of Saxton and Page, Figs. 245, 247. In these machines coils of wound wire are made to revolve by means of mechanical motion in front of the poles of powerful magnets ; by this revolution, the magnets are made to generate momentary currents of Electricity ; by this electricity, when transmitted through carbon points, intense Heat and Light are produced, and chemical decomposition effected, as is shown by the use of the light for the illumination of Light-houses, and by the precipitation of the metals from their solution^ in the various processes of electrotyping and plating. Thus Mo- 4Si. How can it he shown that tho chemical Forces are convertible? H"w can they be traced back to Mechanic 1 Motion? Bv whit machines c.iu the derivation of the chemical forces aud their convertibility be shown? 524 AMONG THE CHEMICAL FORCES. tion may be converted successively into all the Forces and be made to appear as Heat, Light, or Electricity. The do eness of this relation is conclusively shown by the following elegant experiment of Mr. Grove. A prepared daguerreotype plate of silver coated with Iodine is enclosed in a box filled with wa- ter, having a glass front with a shutter over it. Between this glass and the plate is a gridiron of silver wire. The silver plate is connected with one extremity of the coil of a dedicate galvanometer. The gridiron of silver wire is connected w!th one end of the helix of Breguet's metallic thermometer, Fig. 50. The other extremities of the galvanometer and the ther- mometer, are connected by a wire, and the galvanometer needles are brought to zero. Thus a complete galvanic circuit is con- structed: the prepared daguerreotype plate is the battery gene- rating plate ; the silver gridiron, the conducting plate ; the wa- ter in the box, the exciting liquid, and the wire which runs to the galvanometer, thence to the thermometer, and then back to the silver gridiron, is the conducting wire. As soon as the shut- ter which covers the glass front of the box is raided and a beam of day-light, or of the electric light or of the oxy-hydrogen blow- p : pe, is permitted to fall upon the silver plate, the needle of the galvanometer begins to move, and the index of the metal- lic thermometer to turn, showing the circulation of electric- ity, with the production of magnetism, and the evolution of heat. Thus Light being the initiating force, we get chemi- cal action on the plate, electricity circulating through the wires, magnetism in the galvanometer, heat in the thermometer, and motion in the needles. This proce-s sometimes goes on upon a great scale in the ope- rations of nature. Thus by the action of the Light of the Sim upon the leaves of plants, the carbonic acid which they inspire from the air is decomposed, and the Carbon, which constitutes a large part of the substance of plants, set free. It is by this process that the Carbon which now constitutes the vast depots of coal buried beneath the soil has been withdrawn from the ancient atmosphere of the earth. By this action of Light, in virtue of which this Carbon is withdrawn from chemical com- bination, an equivalent amount of chemical force is created, and the liberated carbon, recornbining with the oxygon of the air, will produce an equivalent amount of Heat. The Heat thus set free produces by its effect on water, an equivalent amount of Describe Mr. Grove 1 * experiment. W!i-\f. is the initiating Force in this experiment ? In what operation of nature is this process carried on upon a large scale ? jDescribe this process. THE EQUIVALENCY . 525 molecular motion resulting in the formation of steam, an-1 this in turn produces a definite amount of mechanical motion in tli3 Steam-Engine, which if applied to the revolution of the coils of a Magneto-electric machine, would evolve a sufficient amount of electricity to set free, by means of carbon points, an amount of Heat and Light, provided nothing were lost in these repeated transfers, exactly equivalent to the Heat and Light of the original sunbeams whose active agency enabled the leave? to decompose the carbonic acid of the atmosphere. It wa*, therefore, not without reason that Mr. Geo. Stephenson, th;3 inventor of the Locomotive, ascribed the power that drove it to the light of the sun. " Can you tell me," he said to Dr. Buck- land, " what is the power that is driving that train ? " "I sup- pose it is one of your big engines." " What do you say to the light of the sun ? " " How can that be ? " " It is nothing else ; it is light bottled up in the earth for tens of thousands of years, light absorbed by plants and vegetables being necessary for the condensation of carbon during the process of their growth and now after being buried in the earth for long ages in fields of coal, that latent light is again brought forth and liberated, nwle to work as in that locomotive for great human purposes.'* From the mutual convertibility of these three Forces, it is evident that, when any one of them disappears, and seems to be destroyed, it may in fact only be undergoing a process of con- version into one of the other two, and presently re-appear in an- other form. The motion of a rapidly moving ball seems to be annihilated by strikfng against the target, but in reality it is only converted into another force, viz., that of heat, as is proved by the rise of temperature both in the ball and target. Force, there- fora, disappears in one form to re-appear in another. And not only is this true, but, the new Fore - thus produced by de-volu- tion out of another, is exactly equivalent in amount to that of the Force which has disappeared. 487. In every case of the convertibility of the Chemical Forces, there is an expenditure of the original Force, and a re- duction of its strength exactly equivalent to that of the new Farce produced, into which it has been changed. In all cases where a given amount of force is in action, if the result be the production of a second force, the original force is reduced in State Mr. Stephenson "s opinion of the origin of the power driving the Locomotive. What becomes of the original Force in all cases of apparent disappearance? 487. Is there any proportion between the original Force and the new one into which it is con- verted ? 526 OF THE CHEMICAL strength to a degree exactly proportioned to that of the new force called into being. Thus when the movement of a defi- nite amount of galvanic electricity produces a development of heat in a conducting wire, the amount of electricity in circula- tion is diminished to a degree exactly equal to the amount of heat brought into action. When the rapid motion of a wheel results in producing great heat in the axle, there is a retarda- tion in the motion of the wheel, exactly equivalent to the de- gree of heat excited in the axle. This is very beautifully and conclusively proved by the ex- periment of M. Favre, referred to in 360. A voltaic bat- tery, and an electro-magnet actuated by it, were placed in two adjacent calorimeters somewhat similar to that of Lavoisier and Laplace, 232, and the heat produced in a given time within the battery, when the connection with the electro-mag- net was established, ascertained : the electro-magnet was then made to raise a weight, or in other words a portion of the pow- er of the battery was converted into motion, and the amount of heat in circulation during a space of time exactly equal to the former again noted. It was found that the heat within the batte- ry was diminished in exact proportion to the amount of mechan- ical effect exerted, and the amount of heat which disappeared was found by calcu- Fig. 269. lation to be exactly equal to the amount of heat which this mechanical power thus produced, was capable of evolving, according to Joule's Law, 25 4, i.e, a de- finite amount of Heat had been resolved in- to a definite amount of mechanical mo- tion, exactly equal to the mechanical mo- tion required for the production of an equal amount of heat, the process being reversed. Motion Converted into Heat. Describe M. Favre's experiment by which the equivalence of the new Force to the original Force is proved. What was the result ? \ FORCES. 527 The same fact is shown with equal conclusiveness by an ex- periment of M. Foucault ; if a thin circular disc of copper c, Fig. 269, be mounted on a shaft between the poles of a powerful elec- tro-magnet in the equatorial axis, it can be made to revolve with great rapidity by means of the multiplying wheel M, so long as there is no connection between the electro-magnet and the battery, and this movement will continue for some time after the propelling force is withdrawn, from the momentum it has acquired. If, at this moment, the connection with the battery be established so that the electro-magnet becomes powerfully magnetized, the motion of the disc is checked by the dia-mag- netic action, 39 2, exerted upon it, and by the secondary electrical currents 447, induced within it by the action of the electro- magnet, and it becomes exceedingly difficult to turn it ; at the same time the temperature of the disc instantly rises ; in other words, the force applied to the wheel remaining the same as before, and not being able to expend itself in the production of motion, is converted in part into heat, and the disc at once becomes very hot ; in one experiment the temperature ro.-e from almost 55 F. to 165. It has been stated, 470* p. 497, that when an armature carrying a coil is made to revolve between the poles of an electro-magnet it beco:nes much more difficult to turn it, and its speed is greatly reduced the instant the battery current is made to circulate through the electro-magnet : by en- closing such an armature in a glass tube filled with water, and causing the whole to revolve between the poles of the electro- magnet, Mr. Joule has endeavored to estimate the amount of heat into which a portion of the mechanical force has been con- verted, by the rise of a thermometer placed in the water. In like manner, if the poles of a galvanic battery be joined by a thin platinum wire, the wire will be ignited and a certain amount of chemical action will take place in the battery, a defi- nite quantity of zinc being dissolved, and of Hydrogen set free in a given time, resulting in the production of a definite amount of electricity circulating through the wire, of which a portion is converted into heat. If now, the platinum wire be placed in water, its conducting power will be increased in consequence of the diminution of resistance by the reduction of temperature, a larger amount of the electrical force will be converted into heat than before, and the chemical action on the generating plates within the battery will be found, on examination, to have been correspondingly augmented. If the experiment be re- Describe M Foucault's experiment. If a portion of the power of the battery be ex- pended in the production of Hf" t what effect is produced upon its chemical power? 528 THE INDESTRUCTIBILITY wV versed and the wire be placed in the flame of a spirit lamp, by which its conducting power for heat is diminished, 333, the chemical action is correspondingly reduced. These instances might be multiplied indefinitely, and it is now a generally received truth that when one Force is convert- ed into another, the strength of the original Force is propor- tionably reduced, and that the strength of the new Force is ex- actly equivalent to the diminution in the strength of the Force from which it has been derived. 488. The Convertibility and Equivalency of Force, true of all the Forces which act on Matter. Not only is the converti- bility and equivalency of Force true of the Forces, Heat, Light and Electricity, but also, it is thought, of the other Forces which act on Matter, viz : the attraction of Gravitation and the attraction of Chemical Affinity. This seems to be pretty con- clusively proved in the case of Chemical Affinity fi om the in- stances cited above, in which the amount of Chemical Force in action in the battery is increased or diminished in proportion to the increase and diminution of the strength of the Forces to which it gives rise. But the convertibility of Gravity into new Forces, and of other Forces into Gravity, has not as yet been so conclusively shown. This is a step w r hich yet remains to be taken. At present we may be justified, perhaps, in regarding Gravity and Chemical attraction, i. e.,the Force of attraction which masses of inert matter exert reciprocally upon each other, by which they are drawn together; and the Force of attraction which the atoms of different elements and the more simple chemical compounds exert upon each other, by which they are bound together, and united into the various compound substances which we see around us, as Primary Forces impressed upon all kinds of matter, no portion being exempt, and the latter made capable of modification ?nd control, from the action of the Sec- ond ry Forces, Heat, Light and Electricity, which have just been described. 489. The Indestructibility and Conservation of Force; the Correlation of the Forces. It results as a consequence, from this principle, that, when a new force seems to be devel- oped by the action of one formerly existing, there is no crea- tion of Force on the one hand, and no destruction of Force on the other, but merely a conversion of one Force into another. 488. Is the convertibility and equivalency of Force true of all the Forces ? What is sal! in regard to th attraction of gravitation, and of chemical affinity ? 489. What consequence results from this principle ? AND CONSERVATION OF FORCE 529 Force is therefore believed to be as indestructible as Matter. By this expression it is not meant that either Force or Matter are absolutely incapable of destruction, but simply that in fact, neither of them are destroyed in the various transmutalioris which they undergo, but are merely changed from on^ foi'm to another. The sum total of Force in the U.iiver=e, as well as the sum total of Matter always remains the same, but both may be transmuted from one form into many others. There is never any fresh creation of either. This is what is signified by the Term, now very generally in- troduced into Science, the Conservation of Force, i. e., no Force is ever destroyed ; and the convertibility of the various kinds of Force into each other, in virtue of which this Conservation of Force is maintained, is of;en designated by the term, Co-relation, or Correlation of the Forces. These terms were first intro- duced, and the truths wlnVh they were designed to express, were first advoca!ed in England by Mr. Grove, the distin- guished inventor of the Nitric acid Ba:tery, in 1842. The same general doL-trine of the mutual relations of the Forces, was put forth about the same time by Mr. Joule, in England, no:ed for his determination of the mechanical equivalent of Heat; by Mayer, in Germany, and Colding, in Denmark. The idea that Heat and Motion are two different forms of tha same Force, and mutually convertible, wa* first advanced by the celebrated Montgolh'er about 1800. The same idea was set forth independently by M. Carnot, in 1824, and worked out more elaborately in his bouk upon " Tne Motive Power of Heat." Mr. Grove conceived the same idea at a some- what later period, independent of both the former, and was the first to treat the subject in a systematic manner, and give it a scientific form. It is one of ihe most important advances made in Physical Philo ; ophy in the present century, and is the line upon which research is now rapidly progressing. Tne mo-t important works upon the subject are, Grove, on the "Correla- tion of the Physical Forces" and Tyndall, on "Heat Considered as a Mode of Motion" 90. Heat and Electricity the chief Ag-ents used by the Cheraist, in his investigations. Tha Isamp and the Galvanic Uaitevy his chief Instruments. Or' the three Chemir-al Forces, Heat and Electricity are the most important to the chem- ist in canying on his researches into the composition of What is meant by the terms Indestructibility and Conservation of Force? How te this Conservation maintained ? What is meant by the term Correlation of th Who introduced these terms ? Give the history of the progress of these ideas. 530 ^CONCLUSION. Matter, and in making the modifications which he desires, in the attraction of Cliemical Affinity. While Light is extensively employed by Nature in carrying on some of her most remark- able chemical transmutations especially in the de-oxida'ion of Carbonic acid by the leaves of Plants, and generally in the chemistry of the vegetable kingdom, by the Chemist Light is hardly used in any process except that of taking Photographic pictures, and occasionally for effecting a few remarkable com- binations, such as that of Chlorine and Hydrogen for the pro- duction of Chloro-Hydric acid. The chief instruments which the chemist employs for the de- velopment and application of his two Principal Forces, are, for Heat, the Lamp, the Wind Furnace, the Gas-jet, the Oxy-IIy- drogen Blow-pipe, the common Blow pipe, all depending upon the process of Combustion, and the carbon points of the Bat- tery: for Electricity, the Galvanic Battery, the. Magneto-elec- tric machine, the Thermo-electric Battery, and Ruhinkorffs coil. He also employs the carbon points of the battery, and the terminals of Iluhmkorff's coil, for the production of the most intense heat known to man, in his researches into the composi- tion of matter by Spectrum analysis. The Lamp and the Fur- nace were known to the Alchemists ; all the others, from the Galvanic battery down, have been the fruit of the scientific and inventive genius of the present century. 491. The Conclusion of the Chemical Forces. Thus we have briefly con-idered the nature and principal properties of the three active Agents or Forces, by which the attraction of Chemical Affinity is controlled and modified, and described the most important instruments employed in their application. We are now prepared to make this application and to enter upon the examination of the chemical character of the elements of which the various kinds of matter are composed, and the nature and laws of the Force of Affinity by which they are bound together. This constitives the subject matter of Chemistry proper, and will be reserved for a subsequent volume devoted to the consideration qf the chemical properties and relations of the various k : nds of Matter, Inorganic and Organic, of which the Universe con-i ts. 49*. What are the chief Agents used by the Ch*W*t? What use does he make of Light? What use is made of Light in Natuve? What are the chief instruments em- plo.ed by the Chemist for heat ? for elecrricitv ? Which of them were ki.own to the Alchemists? 401, Wbea were toe others introduced ? State the conclusion of the EXPERIMENTS ON GALVANISM. 531 Experiments: Galvanic Electricity, Electro-Magnetism, and .Magneto-Electricity. 1. The Battery. A battery of 12 elements of Grove or 6 of Bunsen, will be large enough to exhibit nearly all the effects of Galvanic Electricity, The zinc plates should be well amalgamated by dipping them first in dilute chloro-hydric acid, until they are thoroughly cleansed, and then into a cup of mercury, 2. The charge for this battery is 1 measure of sulphuric acid to 6 or 8 of water, mixed, and allowed to cool. In case any of the zincs effervesce in the acid, they must be taken out and dipped anew in the mercury. The porous clay cups should be filled with the strongest Nitric acid which can be procured. 3. Bi-Chromate of Potash in solution, is often used in place of Nitric acid in Grove's and Bunsen's batteries, for the purpose of escaping the nitrous acid fumes, which are evolved in large quantity when Nitric acid is decomposed, 1'our parts of Bj- Chromate of Potash are dissolved in eighteen parts of water, and mixed with four p irta of Sulphuric acid. The Hydrogen which penetrates into the porous cup, unites with a part of the Oxygen of the Chromic acid, and reduces it to the state of Oxide of Chro- mium, which remains dissolved in the Nitric acid ; the strength of the battery however is much less than when Nitric acid is employed, owing to the increased resistance. 4. The Connections. The poles may be connected by means of copper wires, well an- nealed, so as to be readily twisted and bent, The ends pf these wires should be bright- ened with a file, or amalgamated by acid and mercury. The tips of the screws connect- ing them with the battery, should also be brightened with a file. This is a precaution of greit importance, as the full power of a battery can not be brought out if the connec- tions be oxidated- The battery should, if possible, be so constructed as to admit of the zinc plates being all connected together by binding cups, so as to form pne zinc plate, and the platinum plates so as to form one platinum plate, as in Fig. 158 ; or, of being arranged alternately, as in Fig. 157. The former arrangement should be adopted for ex- periineuts upon the heating and magnetic effects of the battery, and the latter for expert- meats upon its chemical effect. 5. Position. The battery must be placed in a draught of air, so that the noxious nitrous acid fumes may not be permitted to escape into the room. 6. The Slip hate of Copper Battery. The charge for this battery is a solu- tion of the Sulphate of Copper in water ; a saturated solution of this salt must first be made, and to this added an equal quantity of water. A pint of water at the ordinary teinperature is capable of dissolving one-fourth of a pound of the salt, so that the half- satur ited solution will contain about two ounces of the salt to the pint. The coating of oxide of copper which is formed upon the zinc plate, should always be removed imme- diately after using, by means of the card brush and plenty of water ; if this is neglected tlie zino becomes covered with a hard coating which can only be removed by scraping or fi'ing. The deposit of copper must also be removed from time to time. The zinc plate must always be taken out of the solution when the battery is not in action, but the solution itself may remain in the copper cylinder, as it has no chemical action upon it, but tends to keep its surface in good condition. When the solution in exhausted, it is best not to attempt to renew its power by adding a fresh quantity of the salt ; it should be thrown away, and a new solution prepared. 7. Diaiell's Battery. The charge for this battery is a saturated solution of Sul- phate of Copper acidulated with an eighth of its bulk of Sulphuric Acid, and placed in the outer cup: the solution is kept saturated by crystals of the same salt placed in the colander c, Fig. 151, The inner porous cup is charged with a mixture of one measure of Sulphuric Acid, and seven measures of water. 8. Smsa's Battery. The charge for this battery is one measure of Sulphnria Acid to six measures of water : the strength of the charge may be increased by the addi- tion of bulphunc Acid, until the proportion is reached of one of Acid to four of Water. 9. Tiia Qis Battery. The usual charge for Grove's gas battery, Pis*. 144, is Oxygen and Hydrogen m the two tubes, dipping into a vessel of water acidulated with SulpHime acid. Jther gases however may be employed. Chlorine may he placed in one tube, fi'id Hydrogen in the other, and connected bv acidulated water : the Chlorine nth-arts the H/drogen of the water, forming Chloro-hvdric acid in the Chlorine tube, find the Ox/gea which is set fn>e unite* with the Hvdrogen to form water in the Hvdro-ren tube. Oxygen may be placed in one tube, and Nitrogen containing a piece of Phosphorus in th other: the Phosphorus attracts the Oxygen of the water and forms Phosphoric ^cid in one tube, while the Hvdrogen which is s=<>t free wnites with the Oxvgen of the other tube to form water. With 50 pairs a decidedlv painfnl shock ran be given to a Bjngle person : the wedle of a galvanometer will be powerfully affected ; a brilliant 532 HEATING AND ILLUMINATING EFFECTS.' spark projected between carbon points : Iodide of Potassium and acidulated water may be decomposed, and gas enough set free i the last case to be collected and detonated. Twenty-six pairs were found to be the smallest number that would decompose wa- ter, but four pairs will decompose Iodide of Potassium. A gold leaf electroscope will be sensibly affected. 1 0. That chemical action is the source of the electrical current, may be shown by dip- p'ng an unamalgamated zinc plate into a mixture of sulphuric aci be made to revolve accompanied at the same time by a loud sound, Figs. 253, 254. 255, 256. 23. Observe that the positive pole wears away, while the negative increases in length. 30. With Duboscq's electric lamp, Fig. 161), the image of tiie points may be thrown upon a screen, and the process of transport very plainly seen. 31. If the carbon poles be arranged vertically, as in Fig. 159, and the negative point be replaced by a carbon cup, on which small bits of the different metals are placed, they will burn with great brilliancy, and the emission of their characteristic colors. 32. If the negative carbon cup be filled with mercury, and a piece of moistened pot- ash be placed upon it, the potash will be decomposed, and the metal potassium set free, forming an amalgam with the mercury, from which it may be obtained by distillation. 33. If mercury be placed in a small iron cup connected with the positive po e of the battery, and be allowed to trickle in a very fine stream, through a minute aperture into a lower iron vessel connected with the negative pole, at the moment of contact between the globules of mercury falling from the upper cistern and the lower cup, the mercury is heated to a white heat, and produces a dazzling white light. This is a splendid experi- ment. 34. Chemusal Effects. Decomposition of Water. The poles, in this case, should be made of platinum, and inserted from belo-.v into inverted glass tubes, closed at the up- per end Fig. 162. The water should be acidulated with sulphuric acid, 1 part of acid to 15 parM of water, in order to increase its conducting po .vcr. The hvdrogen will collect in the negative tube, the oxygen in the positive tube ; the former in double the quantity of the Latter. This experiment may be performed with the U tube, Fig. 164, which must be filled with acidulated water; the poles mast be thrust far down into the tubes, so as nearly to touch, passing through corks at tieir mouths : a bent glass tube may be used to convey the gas from the oxygen end; and the hydrogen may be burned as it is formed, from the extremity of another glass tube, drawn down to a very fine bore This makes a very beautiful experiment. 35. Pass the galvanic current, in an apparatus similar to the last, through ch'oro-hy- dric acid. Hydrogen will be discharged in the negitive tube, and may be burned from a fine orifice; chlorine will be discharged in fie positive tube, and may be recognized bv its olor, and its bleaching effect upon solution of sulphate of indigo, whe.i poured into the tube ; also, by its green color. 35. Repeat the same experiment, substituting tincture of litmus, of violets, or purple cabbage, for the indigo; tne/ will at first be turnel red by the acid, and then will be quickly bleached as the chlorine is disengaged, lor the preparation of tincture of pur- ple cabbage, see Expt 16. p. 77. 37. Pass the current through a stron* solution of common salt chloride of sodium, colored blue in both tubes by tiuf ture of cabbage ; chlorine will be discharged in the positive tube, and almost immediately destroy the blue co or. and sodium will be set free in the negative tube; this will be at once converted into soda by decomposing the water, and change the blue color to a brig'it green. 33. Pass the current throug'i aqua :>mmonia, in a similar apparatus. Hydrogen will be discharged in the negative tube, and may te ,'et on fire, as in Expt. 4, and nitiopcn will be set free in the positive tub, as may be shown by its extirguifbJng a lighted t;;j>er. 39. Pass the current through ni ric acid, in a similar tube. Oxygen will be discharged in the positive tube, as may be shown by its effect on a lighted taper, and ret', nitrous acid fumes in the negative tube If a candle, having its wirk glowing red-hot, but not ligited, be introduced into the oxygen tube, it will I e re-lighted : a'uo paper. 40. Pass the current through a strong solution of iodide of potassium : into the posi- tive tube introduce a few drops of solution of starch, and into the negative some tireture of cabbage ; iodine will be set free at the positive pole, and its presence shown by tinging the starch a deep blue, and potassium set free at the negative pole, which will at once be converted into potash by abstracting ox_ygen from the water, and its presence indica- ted by turning the vegetable blue to green. 41. Pass the current through a solution of sulphate of soda, in the U tube, tinged by tincture of cabbage ; the salt wil be decomposed into sulph'uric acid and soda ; the acid appearing at the positive pole, and turning the blue to red, and the soda at the negative pole, changing the blue to green ; if the platinum wires be removed, and the contents of the two branches of the tube shaken together, the acid and the soda will again unite, the red will neutralize the green, and the blue color will be restored. 534 CHEMICAL EFFECTS. s 42. Pass the current through a solution of nitrate of potash, colored blue by the tine* ture of cabbage ; ni'ric acid will be set free at the positive pole, shown by the red color, and potash at the negative pole, shown by the change of blue to green. 43. Pass the current through a solution of chloio hydrate of ammonia (sal ammo- niac ) in the U tube, colored blue by tincture of cabbr.ge ; chlorine will be set free at the positive po'e, discharging the blue color altogether, and ammonia at the negative pole, changing the blue to green. 4*. Pass the current through a solution of carbonate of potash, colored blue by tinc- ture of cabbage ; carbonic acid will be discharged at the positive pole, with effervescence, slightly reddening the blue tincture, and potash at the negative pole, turning (he blue to a deep green. *D. Try the same experiment with a solution of carbonate of soda: carbonic acid will be set free at the positive pole, and soda ut the negative. 46. Try the same experiment with solution of nitrate of lime; nitric acid will appear at the positive pole, and lime at the negative. 47. Kepeat the same experiment with the solution of acetate of lead ; acetic acid will be set free at the positive pole, reddening a vegetable blue, and pure lead at the negative pole. 48. Repeat the same experiment with the solution of nitrate of silver; nitric acid will be set tree at the positive pole, and metallic silver at the negative. 49. Repeat the same experiment with the solution of chloro -hydrate of tin ; the acid will be set free at the positive pole, and tin deposited at the negative pole. 60. Repeat the same experiment with the solution of nitrate ol mercury ; the acid will be set free at the positive pole, and the mercury at the negative. 61. Pass the current through a solution of chloride of calcium, colored blue by tinc- ture of cabbage ; chlorine will be set free at the positive pole, and discharge the bh e color, while calcium will be set free at the negative, which will be at once converted into oxide of calcium or lime, and change the vegetable blue to gre*>n. 52. Repeat the same exper ment with chloride of calcium, colored by the blue solu- tion of litmus ; the color will be removed in the positive tube, but no change produced upon it in the negative. 53. Repeat the same experiment with chloride of calcium, colored blue by sulphate of indigo: the color will be discharged in the positive- tube, but remain unchanged in the negative. 54. Repeat the same experiment with chloride of calcium, colored by black ink ; the black will be discharged in the positive tube, but remain unchanged in the negative. 55. Pass the current through a strong solution of corrosive sublimate (chloride of mercury ) having a little blue tincture of cabbage in the positive tube ; chlorine will be set free at the positive pole, discharging the blue color, and mercury at the negative pole, which should be made of gold foil ; this will be at once whitened by the deposit of the mercury ; a small gold coin will answer very well for the negative pole. 56. Pass the current through a solution of sulphate of topper; sulphuric acid will fee set free at the positive pole, and copper deposited at the negative pole; eon.etimes the oxide of copper is deposited instead of the pure metal ; but if the solution be of moderate strength, the hjdrcgen which is set free at the same pole will decompose the oxide, and set free metallic copper. This is a case of secondary decomposition (see 371 ) and illustrates the art of electrotyping. 57. To decompose potash, pour a strong solution of caustic potash, which has been carefully protected from the ir. upon the surface of mercury in a small iron cup ; con- nect this cup with the negative pole of the battery, then apply to the surface of the solu- tion a platinum wire connected with the positive pole ; oxygen gas will be set free at the positive pole, and metallic potassium at the negative pole, which will immediately form an amalgam with the mercury, giving it a puffy appearance. The potassium may be ex- tracted from the mercury, and obtained in a pure state, by distillation in an atmosphere of nitrogen. BB. Place a piece of solid caustic potash, slightly moistened, upon a flat piece of gas- carbon, hollowed into a cup, and attached to the negative pole of the battery in the in- strument represented in Fig. 159, or in Duboscq's electric lamp, Fig. 160, and then bring down upon it a piece of platinum wire, or gas carbon, attached to the positive pole : oxygen will be set free upon the wire, and the metal potassium in the carbon cup, burning, as it forme, with a beautiful red flame. 59 Another mode of performing the same experiment, is to excavate a small cavity in a piece of caustic potash, introduce into it a globule of mercury, and place the potash upon a plate of platinum ; the positive pole is then to be connected with the platinum plate, and the negative with the mercury ; the potarh is slowly decomposed, oxvgen ?et free at the positive pole, and potassium at the negative, which, as frst as formed amalgamates with the mercury ; it may be obtained in a pure state by distilla- tion in nitrogen, as described in experiment 57. 60. The decomposition of soda, and the formation of metallic sodium, may be accom- EXPERIMENTS ON GALVANISM. 535 plished by subjecting a piece of caustte soda, slightly moistened, to the same treatment ; oxygen will be set free at the positive pole, and metallic sodium at the negative pole, which may be obtained, by distillation, from the mercury. If the experiment be per- formed with charcoal poles, the sodium, as it burns, will emit a yellowish light, and may thus be distinguished from potassium. 61. If some of the potassium or sodium amalgam, obtained in these experiments, be thrown into water, the potassium and sodium will quit the mercury, and decompose the water, on account of their strong affinity for oxygen, uniting with it to form potash and eoda, and setting free the hydrogen, which will at once take lire and burn, with red flame for the potassium, and yellow for the sodium. 62. Kepeat experiment 57, substituting for the solution of potash, a strong solution of chloro-hydrate of ammonia (sal ammoniac) ; the mercury will greatly increase in bulk, and an amalgam be formed with the so-called metal ammonium at the negative pole, while oxygen will be set free at th positive pole. This metal ammonium is supposed to be a compound of hydrogen and ammonia, and to have for its symbol, N H*. This experiment may be varied by placing a piece of solid sal-ammoniac upon a platinum plate, and a globule of mercury in a small excavation made in its upper surface, witii which the negative pole should be connected ; the positive pole should be connected with the platinum plate ; the ammonium amalgam will be formed as before. 63. Pass the current through 4 cups of acidulated water, connected by platinum wires, and arranged 'as in Fig. 168, and observe that two poles are formed in each cup, one of which discharges oxygen, and the other hydrogen, and always in the same order; on inverting a tube, closed at one end, and filled with water, over each pole, an equal quantity of hydrogen will be collected in all the hydrogen tubes, and an equal quantity of oxygen in all the oxygen tubes. 64. Arrange the apparatus as in the preceding experiment; at the same time intro- duce a voltameter into the circuit, (see Fig. 170,) having two tubes, closed at the top, inverted in it, and filled with water ; the same amount of hydrogen and oxygen will be collected in these tubes as in those placed in any of the 4 cups. This shows the equality of the circulating force in every part of the circuit. 65. Arrange the 4 cups as before, except that instead of water, in the 1st cup let a solution of iodide of potassium be placed, mixed with starch ; in the 2d, a strong solution of chloride of sodium common salt, colored blue by sulphate of indigo ; in the 3d, a solution of nitrate of ammonia, colored blue by purple cabbage ; in the 4th, a solution of sulphate of copper ; let the poles in each cup be separated by pieces of thick paper ; connect with the battery, and observe the formation of two poles in each cup, as before, and that the iodine, chlorine, nitric acid, and sulphuric acid, on the one hand, and on the other, the potassium, sodium, ammonia, and copper, are set free at corresponding poles. 66. This experiment may be better performed with U tubes. Take 5 U tubes, fix them in supports, so that they may be placed in a line, and connect them by slips of pla- tinum. Into the 1st, pour a solution of iodide of potassium, having starch mixed wit i it in the left hand leg, and purple cabbage in the right ; in the 2d, a solution of chloride of sodium, colored blue in both legs by purple cabbage ; in the 3d, a solution of nitrate of ammonia, also colored blue in both legs, by purple cabbage ; in the 4th, a solution of sulphate of copper, colored blue in the left hand leg only, with purple cabbage ; and in the 5th, acidulated water. Then connect the starch end of U tube 1 with the positive pole of the battery, and U tube 5 with the negative ; observe that the iodine, chlorine, nitric acid, sulphuric acid, and oxygen, on the one hand, and the potassium, sodium, ammonia, copper, and hydrogen, on the other, are discharged at corresponding poles, showing the similarity of their electrical relations; the iodine may be known by the blue it imparts to starch; the chlorine by its bleaching ; nitric acid, and sulphuric acid, by reddenirg purple cabbage ; the oxygen by its effect on a taper ; the potassium, sodium, and amn o- nia, by turning the purple cabbage green; the copper by its metallic lustre; the hydro- gen by its quantity and inflammability. 67. Arrange three cups in the manner described in 372, filling the three cups with solution of sulphate of soda, tinged blue by tincture of cabbage, and connecting them bv shreds of asbestus, or syphons of glass tube filled with the same solution ; on passing the current, the soda will collect in the negative cup, turning it green, and the acid in the positive cup turning it red, without producing the slightest change in the color of the intermediate cup, though both have passed through it. 68. Repeat this experiment, filling the cup A, on the left, with sulphate of soda, tinged blue ; the cup c, on the right, with pure water, also tinged blue ; and the middle cup B, with strong potash ; on passing the current, the acid will collect in the right hand cup, turning the blue to red. and in so doing, pass directly through the potash in the cup, B, without any hindrance, though the affinity between them is intense ; the soda will collect in the cup A, and turn it green, as before. If the sulphate of soda be placed in the right hand cup, the middle cup be filled with strong sulphuric ac'd, and the left hand cup with pure water, tinged blue, the soda will pass straight through the acid without affect- 61 6 ELECTHOTYPINGr AND ELECTRO-MAGNETISM. Ing it, notwithstanding the strong affinity between them, into the cup A, audits pres- ence there may be detected by its turning the vegetable blue to green. 69. Arrange the three cups as before, and into the middle eup introduce a strong so- lution of caustic baryta, or strontia ; in the left hand cup, sulphate of soda tinged blue ; in the right hand cup, pure water colored blue ; on passing the current, the sulphate of soda will be decomposed, the soda will collect in the left hand cup, turning it green, but the acid, in passing through the middle cup, will be caught by the baryta, and precipi- tated to the bottom, in the form of sulphate of baryta, while no effect at all will be pro- duced upon the right hand cup. In like manner, if a solution of nitrate of baryta be placed in the right hand cup, strong sulphuric acid in the middle, and pure water col- ored blue, in the left hand cup, the nitrate of baryta will be decomposed, the nitric acid will remain in the right hand cup, but the baryta, on its way to the left hand cup, will be caught by the sulphuric acid, and precipitated to the bottom, in the form of sulphate of baryta : the left hand cup will remain unchanged. 1'or an explanation of this, see 374. 70. Electrotyping, Plating, and Gilding'. Place a small silver coin, having a platinum wire attached to it, in a solution of sulphate of copper, and into the ttn e solution introduce a small piece of zinc ; no change will be produced in either metal so long as both are kept apart, but as soon as a connection is formed between them by means of the wire, copper will be deposited upon the silver ; this shows the tendency of the me- tals to be deposited upon the conducting plate of the battery, which is always negative within the liquid, and positive without, Fig. 139, 140, 166. 71. Let two slips of platinum be connected with the poles of the battery, and intro- duced into a solution of sulphate of copper, the negative pole will at once be coated with copper, while oxygen will be discharged upon the positive. Repeat the same experiment with nitrate of silver ; metallic silver will be deposited upon the negative pole. If acetate of lead be employed, a deposit of metallic lead will be obtained ; and so with other metal- lic solutions. 72. To copy a coin, take an impression from it in beeswax ; then blow over its surface some fine plumbago, in order to give it a conducting surface ; then attach it by a wire to the negative pole of the battery, taking care that the wire actually touches the plumbago, and introduce it into a sulphate of copper solution ; then bring the positive pole of the battery, which may be a slip of clean copper, into the same solution, and the wax mould will at once receive a deposit of copper, which will steadily increase in thickness ; it may easily be separated from the wax and an exact reproduction of the coin obtained. The solution for depositing copper is best prepared by making a saturated solution of sulphate of copper, and then diluting it to one-half, or one-third, of its bulk, with a mixture of one measure of sulphuric acid with eight of water. 73. If the article to be copied be made of plaster, it should be dipped in melted stea- rine, and then coated witb plumbago, as above described, before being placed in the bath ; or, if it be a medallion, it may be wetted by holding it in water, with the face upward, until the liquid has thoroughly penetrated it ; then tie a slip of paper around the rim, and pour melted white wax into the cup thus formed ; the wax impression is then to be coated with plumbago, as above described ; gutta-percha may also be used to take im- pressions. 74. In order to plate with silver, the articles must be well cleaned, and attached to the negative pole, in a solution consisting of two parts of cyanide of potassium, dissolved in 250 parts of water ; to the positive pole, a silver plate must be attached, in order to keep up the strer.gth of the solution. 75. For gilding, articles must be very carefully cleansed and attached to the negative pole, in a bath consisting of one grain of chloride of gold, and ten grains of cyanide of po- tassium, dissolved in 200 grains of water ; a piece of gold must be suspended from the pos- itive pole, in order to keep up the strength of the solution. In performing these experi- ments upon the deposition of metals, many points of detail connected with the strength of the solution, the power of the battery, and the degree of temperature can only be learned by practice. See Davis' Manual of Magnetism. 76. Magnetism, and Electro-Magnetism. The attractive power of the magnet may be shown by applying either extremity of a magnet to a mass of iron filings, or to any collection of small bits of iron ; the filings and iron pieces will attach themselves strongly to each end of the bar. 77. That a. magnet possesses two poles of opposite properties, may be shown by sus- pending a delicate magnetic needle by a thread, ns in Fig. 174, and observing that its north pole is repelled and its south pole attracted by the north pole of a second mag- netic needle held near each pole successively. 78. The repulsive power of the same poles, and the attractive power of the opposite poles of two different magnetic needles may be shown, by trying the effect of each mag- netic pole of a bar magnet successively upon the poles of a delicate magnetic needle, sus- pended by a fine thread. Fig. 174. 79. The directive action of the earth upon a magnet may be shown by mounting a EXPERIMENTS ON GALVANISM. 537 . magnetic needle upon a pivot, as in Fig. 175, and observing that it immediately takes a north and sonth position, and that the magnetic poles very nearly coincide with t~e ex- tremities of its axis. 80. The effect of neutralizing the directive action of the earth upon a magnetic nee- dle may be shown by fastening a second needle, with poles reversed, directly beneath the first, as in the astatic needle, Fig. 176, and observing that the earth no longer compels the needle to assume a north and south position. 81. The non-directive tendency of the astatic needle may be shown by observing that, when moved from the magnetic meridian, it does not tend to return to it again. That it has not lost its magnetic power, may be proved by the action of a bar magnet, when brought near it. 84. The induction of magnetism in a piece of soft iron may be shown by taking up a common nail by the end of a bar magnet, and observing that the extremity of the nail is itself possessed of attractive power, has become magnetic, and will attract a second small piece of iron, when applied to it. and this another, and so on in succession so long as the connection with the original magnet is maintained, Fig. 177. 8 *. To show the dia-magnetic effect of the magnet upon certain substances, suspend a delicate needle of bismuth or antimony by a thread between the poles of a powerful horse shoe magnet, and it will at once assume an equatorial position, Fig. 1(9. Try the same experiment with a stick of Phosphorus. 84, The same dia magnetic power may also be shown by suspending a small cube of copper between the poies of a powerful electro-magnet by a thread of twisted silk, which causes it to turn round with great rapidity ; the instant, however, that the elec- trical current circulates, and the electro-magnet becomes excited, the motion of the cube is completely arrested ; this is not owing to any attractive action exerted by the poles, for it is well known that no such attraction is exerted upon copper, but to a powerful dia-magnetic action, which acts at right angles to the magnetic axis. 8 5. The dia-magaetism of liquids may be shown by enclosing different solutions in small tubes of very thin glass ; if the liquids are magnetic, like the solutions of iron, nickel, and cobalt, the tubes take up their position in the magnetic axis ; if dia-magnetic, like water, alcohol, ether, spirits of turpentine, &c., they occupy the equatorial axis. 88. The dia-magnetism of gases may be shown by the apparatus indicated in Fig. 183 ; also, by placing a lighted candle between the poles of the electro-magnet. Fig. 255, the pillar of gas rising from the wick will cease to ascend, and be turned off at right angles upon a line corresponding with the magnetic equator. 87. To show that the wire carrying the bitter/ current itself becomes magnetic, con- nect the poles of a series of several p lirs of Grove's battery, by means of a short copper wire, and apply iron filings ; they will adhere equally all around the circumference of the wire, forming circular bands ; when the circuit is broken the iron filings will fall off; but if steel filing* be employed, a part of them will remain attached. 83. To show the effect of the gilvanic current upon the magnet, arrange the wire connecting the pole^ of a battery, and carrying the current, on a line running north and south, the direction of the current being from the south to north, and place a delicate magnetic needle, supported upon a fine point, directly beneath ir,, as in Fig. 172 ; the north pole will move to the west, and the south to the east ; place the nee lie above the wire, and on either side, and observe the effect; finally, reverse the current, and observe the reversion of all the movements. 89. The effect of the wire carrving the current, upon the magnetic needle, maybe best seea by making use of a magnetic needle half brass. In this instrument, the steel nee- dle is wholly upon one side of the poiot of support, and is counterpoised by a brass weight on the other side. By this arrangement, the action of the electrical current upon the pole which points to the pivot (let it be the south pole ) can have no influence in turning the mignet, and its motion will be determined solely by the action of the cur- rent upon the north pole. The effect of this arrangement will be, to make the tendency of the magaet to rotate around the pole more apparent, but no actual rotation can be obtained. 90. That the gvlvanic current induces magnetism, may be shown by winding a picre of soft copper wire spirally around a glass tube, in a right hand direction, and connecting' the two extremities of the coil with the poles of the battery ; then introduce into the ' tube a rod of soft iron, and bring a magnetic needle near either end : it will be found that the iron rod has become strongly magnetic, the rorth pole being at the extremity at which the current leives the coil; apply iron filings, or any small pieces of iron, to fie rod, and they will be found to be strongly attracted ; break the connection, and the mng- nerism will be destroyed, and the .'irticles will fall ; re establish the connection, and the magnetism will be restored ; Fig. 182. 91. Reverse the current, and the position of the pole'' will be reversed. 9*?. Wind a wire around a second similar tube, in the left hand direction, and the position of the poles will be reversed, the nortii pole being at the extremity at which the current enters the wire ; Fig. 183. YOLT A ELECTRIC INDUCTION. 9"*. Connect a mounted helix, Fig. 184, with the battery: the helix itself becomes magnetic, before the introduction of the iron rod. as shown by its effect on the magnetic needle, and upon iron filings ; then introduce the iron rod, and observe that the poles of the rod are the reverse of those of the helix, the rod being magnetized by indue ion. 94. To show the de.icacy of the current, measured by the common galvanometer. Fig. 185, provide a piece of zinc, and another of copper, one inch square, and immerse them in a small quantity of acidulated water, taking care that they do not touch each other, then transmit the current through the galvanometer. 95. To show the extreme delicacy of the a&tatic galvanometer, immerse a piece of zinc, and another of copper, about |th of an inch square, in acidulated water, and connect with the astatic galvanometer ; Figs. 188 and 187. 9S. To show tne magnetic influence of the liquid part of the circuit, suspend a mag- netic needle, as in Fig. 188. 97. To show the truth of Ampere's theory, mount a helix of wire, as in Fig. 190, and observe that one extremity is affected with north polarity, and the other with south, as shown by the magnetic needle, when brought near it. 93. Arrange two helices, as in Fig. 191, and observe that they act exactly as two mag- nets would, under similar circumstances. 99. To show that the wire carrying the current, and the magnetic needle, tend to re- volve around each other, and that their action is mutual, try the experiment with De la Rive's ring, Fig. 192, first with one pole of the magnet, then with the other. ) 00. To show the confirmation of Ampere's theory, provide a ring, mounted as in Fig. 193, through which the current is passing, and observe that it arranges itself at right angles to the magnetic meridian. 1 Ol. Transmit the current through the magic circle, Fig. 197, and observe the heavy weights which it will support. 1 021. Suspend a heavy weight from a powerful electro-magnet, and observe the effect of breaking and forming the battery connection ; Fig. 196. 1O3. To illustrate the principle of the telegraph, send the galvanic current through a wire, around a room, by connecting one extremity with the positive, and the other witli the negative j>oJe of a battery, and cause it to circulate through an electro-magnet, having a movable armature suspended over it, at the other end of the apartment, and ob- serve the effect upon this electro magnet of breaking and establishing the battery con- nection ; or use Aiorse's indicator, Fig. 199. 1O*. To show the application of electro-magnetism to the production of motion, make use of the instrument represented in Fig. 208: also any of the electro-magnetic engines sold by the philosophical instrument-makers. 1O5. Volta-Electric Induction. The induction of a secondary current of elec- tricity, by a primary current, may be shown by the apparatus represented in Fig. 214. A delicate galvanometer must be attached by wires to the extremities of the outer, or the secondary coil ; then, on forming the connection between the piimary coil and the bat- tery, the needle of the galvanometer will be deflected in such a way as to indira'e the passage of a secondary current in a reverse direction to that of the primary current ; the instant the connection with the batfc-ry is broken, the needle will be deflected in the opposite direction, indicating the induction of a current in the same direction as the primary current. 10S. That this effect takes place through a considerable distance may be shown by the apparatus represented in Fig. 215. 1 7. That a secondary current is induced by the approach and removal of Ihe pri- mary current may be shown by the apparatus represented in Fig. 216. 103. The induction of a secondary current, in the primary wire itself, or the extra- current, may be shown by the apparatus represented in Fig. 217. 109. The character of the induced extra-current may be shown by the apparatus in- dicated in Figs. 215, 226 ; vivid sparks are produced by drawing the wire of the battery over the piece of ribbed iron, and violent shocks are given. 110. The tertiary and quaternary currents may be shown by Henry's coils. Fig 218. 111. Miene*.o-T31lectrictty. That a secondary electrical current is induced by magnetism, may be shown by the apparatus represented in Fig. 219 On introducing the permanent 'magnet into the interior of the coil, the needle of the galvanometer is deflected powerfully, showing the induction of an electrical current in the ii-verse direc- tion from the currents flowing around the magnet, according to the theory of M. Am- pere. On reversing the magnet, the needle is deflected in the opposite direction. 112. Remove the magnet altogether, and introduce in its place a br of soft Iron: this will become magnetized by induction as soon as a magnet is brought r.eur its free extremity ; at the instant this takes place, the needle of the grxlvanorretor will be ieflectcd as before ; when the magnet is removed, the iron bar will lose its magnetism tod be deflected in the opposite direction. : 113. The same effects may also be shown by the apparatus represented in Fie. 1^4. 1. 14. The production of sparks by the current thus induced, may be shown by the ap EXPERIMENTS OX GALVANISM. 539 paratus represented in Fig. 220. On touching the mounted permanent magnet A B, with the rod of soft iron, N s, wound with a coil of copper wire, tae two ends of whica nearly meet, the iron rod will be magnetized by induction, and at the same instant a bright spark Hash between the wires. Ho. If an electro-magnet, while actuated by the battery current, be brought near a coil of wire connected witn a delicate galvanometer, a secondary current of electricity will be induced. 116. That an electrc-magnet, magnetized and de-magnetized, will induce an electrical current in a closed wire may be conclusively shown by attaching a battery to one pair of the wires of Faraday's ring; Fig. 223. 117. The same fact may also be shown by introducing a bar of soft iron into the cen- tre of the primary coil represented in Fig. 214, on completing and breaking connection with the battery the iron bar is magnetized, and de-magnetized, and a muca more de- cided effect exerted upon the galvanometer than when the coils are used alone. This is a case of Volta-Magneto-electric Induction. 113. The same fact may be shown by the apparatus represented in Fig 2?2, and also that the strength of the induced current of electricity as shown by the galvanometer is proportioned to the number of soft iron wires introduced, or in other words to the size and power of the electro-magnet. 119. Arago's rotations may be shown by the apparatus represented in Fig. 224. 120. Pace's Separable Halicas. The properties of the induced secondary currents may be exhibited by Page's separable helices, Fig. 226 If the handles con- nected with the extremities of the secondary coil be tightly grasped, shocks will be expe- rienced, when the connection with the battery is rapidly completed and broken, either by drawing one polar wire over the rasp, or by the break-piece, even when there are no wires in the interior of the inner coil; introduce the wires one by one, and taesnocks \vi,l gradually increase in intensity till they become intolerable, and the hands become so tightly fastened to the handles that it will be impossible to open them, and the sciutia.i- tions upon the rasp and break-piece will become very brilliant. 121. Instead of the bundle of wires substitute a rod of soft iron, the shocks and sparks will be considerably diminished. 122. If the bundle of wires or the iron rod be introduced gradually, the spark and shock increase as it enters; in this manner the intensity of the shock may be regulated. 123. Pass a glass tube over the iron wires in the helix, and the eifect will remain un- diminished, but if a brass tube be employed, the shocks and sparks will cease alto- gether 124. If the battery wire be moved slowly over the rasp, distinct, powerful single shocks are obtained ; if moved more rapidly, the arms are convulsed violently. 125. The strength of the shock depends much upon the extent of contact surface between the hands and the metallic conductors ; the shocks will be much lessened if two wires be used instead of handles, and still more if t ic wires are held lightly in tae fingers. The shocks are greatly increased if the hands are moistened with salt water. 125. If the handle connected with the positive cup of the secondary helix be held ii the right hand, and the one connected with the negative cup in the left hand, the left hand and arm will experience the most powerful shocks, and be the most violently con- vulse 1. In determining the positive cup, the terminal secondary produced by breaking contact, should be alone taken into account ; the initial secondary may be disregarded 127. If the ends of the secondary wire be put into water,-a peculiar shock mav be taken by putting the fingers or h inds into the w.iter, so as to make the current p is* through them. Th^ current prefers a piss ige through the body to that through the water, between the fingers ; if the conducting power of the water be made superior to that of the human body by the addition of a small quantity of common salt, little or no shock will be perceived. 128. If a delicate galvanometer be connected with the extremities of the secondary coil, the needle will be deflected in opposite directions, and equally far, whenever the battery circuit is completed or broken. 129. When the circuit is broken, over the surface of mercury by Page's circuit breaker, 452, an intensely brilliant spark is seen in both cups, if the quantity of mer- cury is properly regulated, and the mercury is deflagrated in white vapor. 130. If water or oil be poured upon the surface of the mercury the sparks will be- come less intense, but the shocks more severe. 131. If prepared charcoal points (Expt. 25,) are attached to the ends of the secon- dary wires, and held almost in contact, a beautiful light will be produced. 132. If the ends of the secondary coil be connected with two fine platinum wires which have been inserted into glass tubes, that have been melted on the wires so as to cover the ends completely, and then filed away so as to expose the tips of the wires and then these are immersed in acidulated water, (Expt. 34,) not very for apart, the water vill be decompose 1, and Oxygen and Hydrogen set free, both on completing and break- ing the circuit. As the platinum wires are alternately positive and negative, each ga 540 PAGE'S SEPARABLE HELICES, RUHMKORFF'S COIL. will be given off alternately by both wires. The platinum wires may be coated with seal- ing wax instead of glass. The purpose of covering them is to confine the passage of the electrical current to one small and direct path from tip to tip, instead of allowing it to pass between tne wires along the whole length of the portions immersed in tae water. 13^. In performing tne above experiment, rapid discharges are heard in the water, with sharp tickiug sounds audii le at tne distance of one hundred feet, and the extiemi- ties of tne wires appear in the dark, one constantly, and the other in term ittingly, lumin- ous : this ticking noise and the sparks are produced only by the terminal current on breakiug connection with the battery. 13*. A Leyden jar whose iu.-ide coating is connected with the knob by a continuous wire may be slightly charged, and feeble sparks be obtained from it, by grasping the jar with one hand, and bringing its knob into contact with one of the cups of the sec- ondary helix, and then establishing a connection between the other cup of the heiix and. the outside coating of the jar, by means of a wire well insulated from the hiind. 13d. A gold-leaf electroscope, Fig 115, will exhibit a considerable divergence of its leaves, if its cap be touched by a wire connected with either cup of the helix, provided the contact be made at the moment of breaking the battery circuit. 13o. If the instrument be arranged horizontally, and a bar of soft iron enclosed in a brass tube be introduced ioto the helix, and a small key be applied to one end of the bar, although the magnetism of the bar is intermitted with every break in the battery circuit, yet being almost immediately renewed, the key will not fall. This experiment conclusively proves that a sensible time is required for a bar to lose its magnetic power. 137. Ruhmkorii s Coil. To display the action of this instrument advanta- geously, from four to eight cells of Grove's battery are generally quite sufficient. The wires leading from the battery are to be attached to the binding i-crews connected with the primary coil, and great care must be taken to avoid accidental shocks, by breaking counection with the battery, by means of the commutator, until the adjustment of the ar- rangements for the proposed experiment is complete. For the successful exhibition of the capabilities of the coil, the experiments must be performed in a darkened room. Care must be takeu that the condenser is attached underneath the instrument, as de- scribed in 453, pp 442, 443. 138. The great power of the secondary current induced, can be shown by connecting two delicate steel needles with the binding screws of the secondary coil, and bringing them within a few inches of each other ; on establishing the connection with the batte- ry, a secondary current of great intensity will Hash through the wires with vivid sparks ; the distance may be incieased, under favorable circumstances, to twenty inches, or even more. 1 39. The wire from which the current passes remains old enough to be held in the fingers, Fig 232; the other, the negative wire, becomes ?o hot that it melts into a giO- bule of liquid iron, and if paper is held between the -.vires, it rapidly takes fire 140. If a reflection of these points be thrown upon a screen by means of Pubosrq's electric lamp. Fig. 160, a cone of vapor will appear to issue from the point if each wire, but that from the negative wire being the mo.-t powerful, seems to beat back the stream from the positive wire 141. In place of the steel wires, substitute wires of copper, of zinc, of soft iron, of brass, &c.; in all ca^es combustion will take k lace with the j loduction of the charac- teristic liirht of the metal. 142. O'i directing the discharge through balls of the different metals, Fig. 240, the ppectrum lines peculiar to each metal may be seen to great advantage by means of the spectroscope. 14^. On passing the discharge through an exhausted Electric Eg-, Fg. 284, a beau- tiful luminous trail will flash from one ball to the other. Exhaust the receiver more per- fectly and the luminous port on will be traversed by a series of dark bands comentrio with the positive ball. Fig 234, No. 2; the presence of a little vapor of phosphorus renders these bands much more distinct. Apply the finger at the side of the Egtr. at the same time cutting off the connection of the lower knob with tV.e negative pole of the coil, and the trail will suffer a curious deviation towards the finger. Fig- 234, No 3 144. Instead of the Electric Egg. place a tumbler r-f Uranium glass, Fig. 235, lined with tin foil, upon the plate of an air pump beneath a receiver, and brintr down a sliding rol until it touches the metallic lining, then, on establishing a connection with the coil, a beautiful cascade of light will pour over the edge of the tumbler. 145. Pass the discharge from the coil through Geissler's tubes, filled with different gates which have been more or loss exhausted, Figs. 236, 237, and observe the curious stratification which ensufg. 1 4S. Submit the light of Geissler's tubes to observation by the spectroscope, Fig . 240, and observe the beautiful spectra of the gases which are thus brought out. 147. A Levden jar may be charged by connecting the outer coating. Fig. 230, wi'h one of the poles of the coil, and 'he inner with one of the arms of a discharger, the .ether arm of which is in communkatioo. with the opposite pole of the coil, the extremi- EXPERIMENTS ON GALVANISM. -. 541 .ties being two or three inches apart ; allow a few sparks from the coil to pass, and then remove and discharge the jar in the usual manner. . 143. Attach one of the secondary wires to the ball, or rod, of a self-discharging Ley den jar, and tie other to the outside surface, so arranged that the discharger may be brought within half an inch of the ball ; then, on turning on the battery current, the jar will be charged and discharged with great rapidity, and the snapping noise become continuous ; if a piece of paper be held between the knob of the jar and the wire, it id instantly per- forated, but not set on fire. 143. Twist a platinum wire around the knob of a Leyden jar, and bring its end near enough to the poles of the coil to almost touch them without quite doing so, and a noiseless spark of feeble light will pass from each pole to the extremities of tne platinum wire ; if at this moment the outer coating of the jar be connected with one of the poles of the secondary coil, the spark, at the interruption on that side will suddenly become noisy and brilliant ; what is very singular, the noiseless spark will kindle paper and other combustibles, while the noisy flash will fail to kindle them. 1 50. Charge a large electrical battery by cascade, the jars being arranged hori- zontally and in succession, the knob of the first nearly touching the outside coating of the second, and so in regular series. 151. If the Leyden jir be coated with spangles, a spark will appear at each break, and the whole jar be li t up with hundreds of brilliant sparks each time it is charged and dis- charged. 1 o2. When the continuous discharges from the Leyden jar are made to pass through the centre of a large lump of crystals of alum, sulphate of copper, or ferro-cyanate of pot- ash, the whole of the crystal is beautifully lighted up during the passage of the electri- city from one wire of the discharger to the other. 153. The chemical effects of the coil may be shown by causing the secondary current to pass through a tube of air hermetically sealed, Fig. 241 : the Oxygen and ^Nitrogen combine to form Nitrous acid, with the production of red fumes. 1 5 *. Enclose Oxygen in a tube with solution of starch and Iodide of Potassium, Fig. 242, r.nlpas as iccession of sparks fiom the coil, one by one ; the Iodide of l'otas.-ium wiil S3oa bj decomposed, and tae characteristic blue color resulting from t;ie action of starch on free loline be produced, showing the conversion of Oxygen into Ozone. 155. Water may be decomposed by connecting the poles of the coil with two of \Vol- laston's dischargers, consisting of platinum wires covered with glass, the tubes being filled with mercury : Oxygen and Hydrogen will be set free at each pole alternately, and a mixture of tiie two gooses may be collected iu an inverted glass test tube filled with water. 156. The vapor of water may be decomposed by passing a continuous charge from the coil through steam in a glass flask, and a mixture of the two gases collected in an inverted tube, Fig. 243. 157. If the ste*4 wires from the poles be applied to any small animal, such as a rat, or a rabbit, life will instantly be destroyed ; t*'o of Bunsen's cells are quite sufficient. With twelve of Bun.sen's cells a man could probably bo struck dead. A very feeble spark from one small Grove or Bunsen cell may be transmitted through a large circle of persons joining hands. These experiments, however, should be performed with the greatest caution. 158. Mi?n3to-Electric Machines. The best machine for exhibiting the effects of Magneto-electricity is Page's, Fig. 247. On turning the wheel w, by mr.-ms of the ivory handle attached to it, the coils A A, are made to revolve with great r.ipid- ity, and continuous currents of positive and negative e ectricity are discharged from the cups p and N, which, by means of wires, may be used for experiments ia electro- inagnetism, decomposition of chemical compounds, the production of lighf, and the giv- ing of shocks, in the same manner as the wires proceeding from the poles of a galvanic battery. 1 59- This instrument may be made to produce an electricnl current of high or feeble intensity, by making use of coils, consisting of very lo 'g and fine wire, for the former, and of coils composed of short and coarse wire for the latter ; the former is more useful for shocks md chemical decomposition, the latter for heating and magnetic effects. 1 1O. By suddenly breaking tho magnetic current, a secondary current in the same direction of much greater intensity can be induce! ; the breaking of the circuit is ac- complished by me ins of a steel wire, thrust through the cup x, and bearing upon the toothed wheel mounted above the pole changer. For giving shocks, this steel wire should be inserted and firmly fastened in its place ; but for all other experiments it should be removed, and the primary current used alone. 161. Connect the wires proceeding from the poles p and N, with the extremities of a galvanometer, Fi%. 185, and the needle will at once be violently oscillated. 1 32. Connect the polar wires with the extremities of an electro-magnet. F/>s. 1W>, 196, 208, and a very considerable degree of magnetic po.ver will be produced, quito MAGNETO-ELECTRICITY, TH2HMO-2LECTRICITY. k sufficient to raise weights, and produce motion in some of the most simple electro-mag- netic machines. 163. Connect the polar wires with a telegraphic line, and it will be found that mes- sages may be communicated by Morse's Indicator. Fig. 199. 164. By connecting the polar wires with the apparatus represented in Fig. 1G2, wa- ter may easily be decomposed, and the Oxygen and Hydrogen collected in separate tubes or in one ; in the laWer case one cubic inch of the mixed gases will be liberated in five to ten minutes ; it is found that platinum terminal wires answer better with the mag- neto-electric current thin strips of platinum foil for thn experiment. 165. By placing a piece of unsized paper iu the curved part of the u tube, Fig. 1G4, BO as to separate the substances that are Set free at the two poles, most of the experi- ments upon the decomposition of saline solutions described under Expt. 34, of the chem- ical effects of the Battery, may be performed. Sulphate of Soda, Nitrate of Potash, Iodide of Potassium, Sulphate of Copper, Acetate of Le d, Nitrate of Silver, Chloride of Gold, may be decomposed, and these medals, or their oxides, be obtained at the nt g- ative pole. The etherial solution of Gold prepared by dissolving a strong solution of tae Chloride of Gold in Ether, may be substituted for the Chloride of Gold pure. 166. If the polar wires be connected with fine carbon points, Figs. 159, 249, a con- tinuous light of great brilliancy will be evolved. 167. If the polar wires of the magneto-electric machine be attached to the primary coil of Page's separable helices, or lluhmkorCFs coil, all the effects of these instruments may be obtained in the same way as when a galvanic battery i.s employed. 138. The primary magneto-electric current has too low an intensity to afford strong shocks, but these may be increased by making use of armatures wound with a greut length of very fine wire. Secondary currents, however, may be obtained by interrupt- ing the primary circuit, as in the case of Page's separable helices : these have a much higher intensity, and give powerful shocks. The primary current is broken by means of a wire running from N, and pressing upon fie pins rising from the circumference of a wheel mounted on the axle of the coils. Fig. 247. Sec Expt. 1 30. 169. To show that shocks may be obtained from the primary current, the wire that 'plays upon the pins must be removed, so that tiie circuit may not be broken ; tho springs pressing on the pole-changer must neither of them leave the segment which it touches before it comes in contact with the oppo ite segment ; otherwise the circuit will be broken at the pole-changer, an 1 strong secondary shocks obtuiued. Metallic hrmd.cs are then to be connected by means of wires with the cups p and N, and the coils set i.i motion : slight shocks will immediately be exper.enced. These may be partially reg- ulated by varying the speed. 170. To exhibit the shocks produced by the secondary current, the wire leading from 'N, and pressing upon the pins of the horizontal wheel must be inserted, and tue coils set in motion. Whenever the wire is in contact with the pins, the primary current passes from r, through the magnets and axis of the instrument, by the pins and con- necting wire to the cup N, in preference to passing through the body of the subject. But iis soon as the wire ceases to press upon the pins, the primary current is broken, and the same instant a secondary current of great intensity is induced, which is in the same direction with the primary current, and not being able to traverse the instrument, is compelled to pass through the body of the operator, giving a sho< k of extreme inten- sity, increasing with the velocity of revolution ; the hands cannot be unclo? ed, and with a powerful machine, the person through whom it is discharged is prostrated, rolls on the ground, and is at the mercy of the operator. At the same time bright sparks of light sometimes a i inch in length, will flash between the pins and the wires. 171. The shocks may be regulated by varying the speed of revolution ; also by placing an iron armat.jre across the steel magnets, neutralizing their power ; also by passing the primary current through a piece of wet cotton wickjng, one end of which is connected with one of the poles, p or N, and the other attached by a wire to one of the metallic handles. The handles are sometimes one-half of wood ; no shock is felt when either one handle or both'is held by the wooden portion. Sometimes the handle is made of glass or porcelain, tipped'with moistened sponge ; in this case no shock is felt when the handle is held by the glass. The arm connected with the negative cup will be most affected by the shocks. 1 72, Thsrmo-Electricity. Place a bar of copper Upon a bar of bismuth, in the 'manner represented, Fig. 258, and npply a lamp at the point of junction a current of electricity will be produced circulating as represented in the figure. 173. Instead of heat apply cold at the point, o, and an electric current in the oppo- site direction will be induced as indicated by the motion of the needle. 1 74. Construct a battery of several pairs of plates of Antimony and Bismuth, as re- presented in Fig. 260, and observe the great increase of effect. 175. With a Thermo-electric multiplier, which may now be procured of any Philo- -seph>al instrument maker, observe the extreme delicacy with which slight change of temperature are indicated. EXPERIMENTS ON GALVANISM. 543 176. With Farmer's Thermo-electric battery, repeat the various experiments de- scribed above, in connection with the galvanic battery; for the purpose of illustrating its decomposing, magnetic, illuminating, and physiological power : also use it instead of tae battery to actuate Page's and ituhmkorif s Coils. 1/7. Instead of applying heat transmit a current of electricity through a thermo- electric series, consisting of antimony and bismuth. Cold wiil be produced at the first junction, and heat at tae second If tue electric current be transmitted in the same direction wita the thiruio electric current, heat is the result; if m the contrary direc- tion cold will be produced. 173. Animil Electricity. The electric current existing in the animal economy and circulating from the interior to the exterior of a muscle, may be shown by arranging a series of limbs of frogs in such a manner that the interior of one will come into contact with the exterior of the next, so that one of the extremities of the series is formed of the interior of the muscle, while the other is formed of the exterior ; the terminal pieces should dip into cavities, in which a little distilled water is placed. On introducing the wiras of a galvanometer into these cavi ies, and completing tue circuit, a current is produced by which the galvanometer needle is deflected, iodide of potassium is decom- posed, and the leaves of an electroscope, with the aid of a condenser, made to diverge. 173. The same current may also be shown, by stripping the flesh from the upper end of a frog's leg, so as to display the nerve, and then dipping the extremity of tae nerve into one vessel of acidulated water, and the foot of the frog into another, and then con- necting the two- vessels of water by means of a curved wire ; as soon as the circuit is completed, the leg of the frog is perceptibly convulsed. 1 3D. A frog's leg miy be used as a g ilv moamfer, by stripping down the flesh so c,s to expose the nerve, and then inserting tae resf of the limb in a small glass tube, the ne/ve hanging out: whenever an electric current, however slight, is made to pass through the nerve, the leg H immediately convulsed : it is said that such an arrange- ment is 50,OJO times more delicate tain the most delicate gold leaf electroscope. 131. Paysiotojioil fifasts of tia Cirraio. Expose the nerve of the leg of a frog, and twist a bit of copper wire around a piece of zinc ; then touch the nerve wita the zinc, and the outside of the leg with the copper : at the moment of contact the leg is convulsel ; disconnect the t.vo matils, and the convulsions cease, though they may still be in contict with the animal. Each time the zinc and copper are made to touch, the convulsions are renewed. 132. Place a live Bounder 01 a plate of zinc or pewter; and bring a silver spoon in contact with its back; there will be no convulsion, but if the spoon be made to touch the plate while it rests on the tHh, tie animil beco:nes strongly convuNel. 133. If a piece of silver be placed above the tongue, and a piece of zinc beneath it, no sensation is perceived so long as the metals are separated, but if they touch each other, a peculiar tingling sensation or taste is experienced. If tho silver be placed between the upper lip and the teeth, instead of under the tongue, a flash of light will appear before the eyes. 131. A o p a, rat a *. The apparatus for the performance of the experiments described in this work, may be obtained of the following Philosophical instrument makers : E S. Ritchie, N. B. Chamberlain, Boston; B. Pike & Sous, New York; W. Y. McAllister, Philadelphia. * LI .IUI A .{ , , V KUSITY OF VIRG. GE JR. II , 4 0. " FINI9. INDEX. 2f. B. The Numbers refer to the Pages. A. ABSORPTION of heat, 56. " in ebullition, 128. Action of the same current on successive chemical solutions, 359. Air, compression of, evolves heat, 225. " specific heat of, 219. " expansion of, by heat, 93. " weight of, ti. " thermometer, 101. Aldebaran spectrum of, 265, 275. Amalgam for electrical machine, 311. Amount of vapor formed proportionate to temperature, 17. Ampere's theory of magnetism, 331. 'i " supported by magneto- electric induction, 449 Animal electricity, 511. Anomalous effect of heat on water, 9o. Apparatus. 543. Applications of electro-magnetism to mo- tion, 409. Applications of expansion by heat, 80. Arago's rotations, 44ti. Arc, voltaic, 345. " influence of magnetism on, 505. Arcturus, spectrum of, Go, 275. Ascension of heated liquids and gases, 41. Astatic needle, 371 ' galvanometer, 379. Atlantic telegraph cable, 403. battery, 403. " " history of, 408. signal instrument, 406. " " rate of transmission by, 407. Atmosphere, peculiar properties of, 5. B. BATTKRIFS, Cruikshanks,Bunsen's,Grove's, Danieirs. Smee's, 331-337. _ Batteries, management of, 837. Batteries of quantity and intensity, '80. Peltegeux, spectrum of, 2i5, 275. Bismuth an eminently dia-magnetic sub- stance, 373. Black, Dr. Joseph, the discoverer of the Laws of Latent Heat, 124. discoverer of absorption of heat in vaporization, and evolution in con- densation, 130. Black Dr. Joseph, account of the succes- sive steps in the improvement of the Steam Engine, 141. Boiler of the steam engine, 146. Boiler of locomotive, 1*2. Boiling point influenced by atmospheric pressure, 131. measurement of heights by, 132. influence of adhesion on, 133. influence of air in water on, 134. influence of solids in solution on, 134. raised by increase of pressure, aud lowered by diminution, 134. Breguefs metallic thermometer, 110. JJimsL-u's Battery, 33T. C. CAESIUM, 269. Caillaud's Battery, 397. Caioresceuce of rays of heat, 74. Calorimeter of l^avoisier and La Place, 214. Capella, spectrum of, 2oo, 275. Camera, photographic, 283. Carbonic acid, solidification of, 196. Carre's Ice Machine, 204. Change of density produces change of temperature, 221. Charges for batteries, 531. Chemical constitution of water, 319. " effects of the battery, 348. " rays, range of, in solar spectrum, Fluorescence, 259. " rays of the solar beam, 258. Chemistry, origin of name, 1. " nature of, 1. " a science of experiment, 9. " differs from >.utural Philoso- phy, 8. connected with tho Arts, 10. medicine and agriculture. 11. " depends upon the balance. 14. fundamental princ iple of, 15. active agents of, 19. Circuit breaker. 452. Circumstances influencing evaporation.,181. Cold produced by evaporation, 181. Compensation pendulums, 88. Compound nature of light, 253. Condensation of steam, 139. Condensing steam engine, 143. Condenser, attached to lluhuikorff's coiL 456. i CON 545 EXT Convection of heat in liquids, 37. ' in gases, 33. Convertibility of forces, and indestructi- bility , 2.44. Copper piat of the battery, part played by, 320. Copper sheathing, protection of, 363. Crown of cups, Volta's, 330. Cruikshank's battery, 331. Cr^ophorus, 184 Culinary paradox, 137. D. DAGUERREOTYPE process, 280. Dalton's law of the tension of vapors, 174. Daniell's battery, 333. hygrometer, 189. pyrometer, 110. Davy, Sir H., extraordinary galvanic ex- periment, 358. the discoverer of the electric light, 346. Decomposition of water by the battery , 350. Decomposing tube, 35 1. Decomposition of metallic salts. 353. of metallic oxides by the battery, 52. of water, 350. De la Rive's ring, 384. De Luc's pile, 339 Despretz' experiments upon the conversion of Carbon into diamond, 477. Dew, how produced, 191. Dia magnetism of gases, 373. Dia-thermancy of solids, 61. of liquids, 64. " of gases, 65. Difference between galvanic and statical electricity, 341. 500. Different kinds of heat. 66. Directive action of the earth, 370. Disappearance of heat in liquefaction, 113. Distillation, 164. Double refraction and polarization of heat, of light, 252. Draught of chimneys, 93. Duboscq's electric lamp, 345. E. EARTR a part of the telegraphic circuit, 398. Ebullition, 127. Elastic force of vapor, varies with tempera- ture, 174. Elastic force of vapor in two connected vessels, that of the colder, 177. Flement, definition of, 16. Electricity, nature of, 290 two theories of, 300. " two kinds, Vitreous and Resin- ous, 293- " statical. 289. galvanic, 311. " sources of, 291. * effects of, 307. Electricity, induction of, 296. " of the machine distinguished from that of the battery, 500. " and magnetism, effect of on. light, 504 " induced by induced magnet- ism, 440. " induced by the magnetism of the earth, 448. Electric gas-lighting, 420. lire alarm, 417. " light, not produced by combus- tion, 346. lamp, 346. " telegraph, 387. Electrical insulation, '294. ' machine, 301. tension exists before the passaga ' of the current, 823. Electrified bodies repel each other, 293. " attract each other, L93. Electro-magnetism, 367 laws of, 381. " experiments on, 532. magnets, 376. " magnetic clocks, 415. " locomotives, 412. " motor of Froment, 410. " positive and negative bodies, 361. Electrophorus, 305. Electroscope, 293. Klectrotyping, 364. Electro-chemical order of the elements, 361. Equatorial magnetic position, 373. Evaporation, 169 " of different liquids, different, 179. " in a vacuum is instantan- eous, 172. Expansion produced by heat, 79. " of liquids, 91. of gases, 92. " of water in vaporization, 138. Expansive power of steam increases with temperature, 155. Expense of electro-magnetism compared with steam, 414. Experiments on conduction, convection, radiation, and transmission of heat, 76. on effects of heat, expansion of solids, liquids, and gases, 110. on liquefaction, 125. on vaporization and steam, 167. on evaporation, 209. on specific heat, 231. on sources of heat, 237. on light, 287. on electricity, 310. on gal vanfsm, electro-magnetism, mag- neto electricity, thermo electricity, animal electricity, 531. Experiment of the three cups, 357. Explosions of steam boilers, 150. " explained by the spheroidal state, 162. Extra-current, 433. FAH 546 HtTA F. FAHRENHEIT'S scale, 105. " reduced to Centigrade and Reaumur, 107. Faraday's discovery of Volta electric in- duction, 425. discovery of induction of electricity by electro magnetism, 444. discovery of the effect of magnetism on polarized light, 506. Farmer's thermo electric battery, 516. Fire-syringe, 225. Fizeau's discovery of the effect of the con- denser upon Ruhmkorff 's coil, 457. Flame, dia magnetism of, 505. Fluidity, heat of, 116. Fluorescence, 59. Fluxes, 121. Foci for heat, light, and chemical rays dif- ferent, 261. Force of expansion by heat, 82. Forces, indestructibility and convertibility of, 244, 5. Fraunhofer's lines in solar spectrum, 263. explained by Kirchhoff, 271. displayed upon a screen, 265. instrument for observing, 264. Freezing mixtures, 119. " of water in vacuo, 183. of water, anomaly in, 98. " point of water lowered by salts and acids, 12 . of water, heat evolved by, 117. " of mercury in red hot crucible. 199. Friction a source of heat, 235. Frog battery, 519. " Galvani's experiment on, 313. Froment's electro-motor, 410. Fuel not economized in using other liquids than water, 158. not economized in boiling water at a low temperature, 15'>. Fusing point, why fixed, 116. " " of different substances, 113. G. GAIVANI'S theory, 312. Galvani the discoverer of galvanism, 312. Galvanism, discovery of, 312. Galvanic electricity, 3 II. Galvanic electricity produced by chemical action 317. Galvanic battery, 329. Galvani -. batteries of historic note, 341. Galvanometer, 3/8. Gases, dia-magnetism of, 373. '' dia-thermancy of, 65. " expansion of, by heat, 92. " nature of. 194. liquefaction of, 194. peculiar properties of, 5. constitution of, '94. " poor conductors of heat, 34. " liquefaction of, 194. " solidified, 199. 23 Gas battery, 327. Geissler's tubes, 469. " " applications of, 472. Globe, constitution of, dependent upon temperature, 2l8. Graduation of thermometers, 105. Grove's Nitric acid battery, 335. " gas battery, 3^7. Grove on the correlation of Forces, 529. Gymnotus, 517. II. HARRISON'S compensation pendulum, 88. Heat, nature of, 22, !i37. " seeks an equilibrium, 25. " conduction of. in solids, 26. ; the cause of evaporation, 169. " explained on the mechanical theory, 241. " light and chemical effect, relations of, in the solar spectrum 287. <{ of the battery and mechanical equiv- alent of heat, 317. 1 produced by motion, 235. 41 converted into light 243. 1 rays of solar beam, 258. ' sources of. 232. " evolved in solidification, 117. " latent, 112, 115. ' specific, 210. 1 produces expansion, 79. " radiation of, effect of surface on, 43. ' reflection of, 48. ' refraction of, 67. 1 double refraction of, 75. " in voltaic circuit, Favre's experiment, 347, 517. " evolved in condensation of steam, 129. " latent in steam, 128, 145. " specific of solids, 216. 11 " liquids, 216. " " gases, 217, 218. ' " Rejfnaulfs table of, 219. " " altered by change of density, 220; diminished by com- pression ; increased by ex- pansion, 221. ' conduction of. in liquids, 33. " of. in gast-s, 34. " convection of, in liquids, 37. '" " gases, 38. " propagation of, through liquids, 40. ' reflection of, by fire-places, 55. " absorption of, affected by color, 57. " Melloni's apparatus for measuring small degrees of, 63, 514. " rays of solar beam, unequal refran- gibility of, Sir H. Englefield a ex- periments, 68. 1 Sir W. Herschel's experiments, 69. " experiments on conduction, radia- tion, reflection, transmission, ef- fects of, 110. Heated particles of liquids, their ascension how explained, 41. HEA 547 MAG Heating effects of galvanic battery, 343. Henry's coils, 436. " discoveries in electro-magnetism, 421. in telegraphy, 422. " of the extra-current, 438. High pressure steam-engine, 142. History of Atlantic telegraph, 408. " of discovery of induction of elec- tricity by electro magnetism, 444 " of discovery of magneto-electric induction, 442. " of discovery of extra current, 438. " of discovery of electro-magnetism, 421. " of discovery of Yolta-electric in- duction, 425. " of discovery in the construction of induction coils, and magneto - electric machines, 508. " of the theory of the correlation of the Physical Forces, 529. Holmes' magneto-electric machine, 488. Horse shoe electro magnets, 386. Hydro-electric machine, 306. Hydrogen, how transferred within the bat- tery, 319. cooling effect of, on red-hot wire, 36. Hygrometer, Daniell's, Saussure's, 189. I. Ice Machines, 204, 227. Ice, specific heat of, 217. Indium, 259. Induction, theory of, 298. " on the approach and removal of the primary current, 429. " conditions of, 431. " takes place through a consid- erable distance, 427. " coils, Page's, Ruhmkorff's Ritchie's, 450, 454, 460. 1 ' of magnetism , 3 72. Insects, temperature of, measured, 515. J. Jacoby's electro-motor, 412. Joule's Law, 236 Joule, experiments of, on mechanical equi- valent of heat, 236. K. KirchhofTs discovery of the coincidence between the dark lines of the solar spec- trum and the bright lines of metallic- spectra, 271. L. Ladd's magneto-electric machine, 497. Land and sea breezes, 39. Latent heat, 210. " " of condensing engine, 145. Law of chemical decomposition by the bat- tery, 361. Leyden jar, 302. " " charged by Ruhmkorff's coll, 463 ' by Page's separable helices, Light, nature of, 246. " sources of, 247. " reflection of, 250. " refraction of, 251. ; double refraction of, 252. 1 solar, compound nature of, 253. " number of vibrations required to produce the different col- ors, 256. " " heat rays of, 256. " " chemical rays of, 258. " " decomposition of, 2;~>4. ' triple character of, 260. " " spectrum of, crossed by dark lines, 263. " " spectrum of, crossed by bright lines, 273. " effect of, on plants, 277. ;< effect of, on chemical com- pounds, 279. " on daguerreotype plates, 280. " on photograph paper, 284. " " relations of the rays of heat to those of light and chemical effect, 287. " experiments on, 287. ft artificial, spectra of. 262. " of magneto electric machine ap- plied to illumination. 487- " brilliancy of that produced by Wilde's magneto-electric ma^ chine, 494. " of the voltaic arc, 347. " effect of electricity and magnetism. on 504. " of Ruhmkorff's coil affected by the magnet, 471. " comparative cost of producing by Smee's battery, Groves's by illu- minating gas, the magneto elec- tric machine, 517. Lightning, spectra of, 276. Liquefaction produced by heat, 113. " always attended by reduction " of temperature, 118. Liquids poor conductors of heat, 33. " peculiar properties of, 4. Luminous effects of galvanic battery, 344. M. Magic circle. 387. Magnet described, 369. Magnetic and dia-magnetic bodies, 372. needle, influence of the battery cur- rent on, 368. needle acted upon by the liquid part of the circait, 3Su. poles, mutual action of, 370. effects of the battery, 367 Magnet, influence of, on the voltaic aro. 504 MAG 548 SAN Magnetism of a helix carrying a current, 332. of the earth affects the wire carrying the current, 385. Magnetic curves, 4*8. " field, 3.3. " poiarizttioa of light, 494. " telegraph, 38<". Magneto-electric induction, 439 " electricity used in the arts, 485. , electric machines. 477. electricity applied to the illumina- tion of iig. it-houses, 487. Management of batteries, 337. MAP of solar spectrum, 263, 270, Mircet's appiratus, 133. Material taeory of heat, 237. Matter indestructible, 15. " jtaree principal states of, 3. Measurement of heights by boiling point, Mechanical theory of heat, 239 " equivalent of heat, 23">. Melloni's researches on heat, 6J, (33, 64, 5l4. thermo multiplier, 514. Mercury, specific heat of, 212. u frozen in red-hot capsule, 164. Metals, relative conductivity of, for heat. 27. conductivity of, for electricity, 28. taerino electric order of, 512. deposited from their solutions, 353. discovered by spectrum analysis, 26d. Metallic connection between the plates not . neoessary for galvanic action, 3^6. Meteors, spectra of, 276. Mirrors parabolic, effect of, on rays of ligat, 5). Molecular movements in magnetization, 3tS. Moon, spectra of, 275. Morse's telegraphic indicator, 390. " alphabet, 3J2. Motion produced by heat, 239. Muscular electric current, 518. N. NATTERER, process for liquefying gases, 200. Nebulae, spectra of, 276. Nicholson and Carlisle, their discovery of the decomposition of water by the bat- tery, 348 Nitrogen, spectrum of, 470. Nobili's Thermo-electric battery, 513. 0. OXYGEN, a magnetic substance, 374. P. PAGE'S electro-magnetic locomotive, 412. '' pole changer, 484. '" magneto electric machine, 483. " separable helices, 450. Papin's digester, 159. Phosphorus a dia-magnetic body, 373. Photography, 281. Photographs produced by the chemical rays of the solar beam, ^8*. f'hysiological effects of tae battery, 520. Plate electrical mac bine. 3' '2. Poinc.? of resemblance between static and gdivauic electricity, 340, 5u2. of difference, 3-il, 483, 5UO. PolartzatioH of heat, 75. ' of light, 152. " and transfer of the elements necessary for galvanic ac- tion, 321. Poles of voltaic battery, 307, 321. Positive and negative poles of the battery, how determined, 34(J. Potassium, spectrum of, 270. Pressure, how transmitted from boiler to cylinder, 15'>. Prism, its effect on the solar beam, 253. Procyon, spectrum of, 26o,275. Progress of discovery in galvanic induced electricity, and induction coils, 5u8. of discovery in electro-magnetism, 421. Propagation of pressure through, fluids, 149. Pulse glass, 188. Pyrometer, Daniell's, 110. R. RADIATION of heat, 42. Itain and snow, production of, explained, 226. Reaumur's thermometer, 106. Reflection of light, 250. ' of heat, 48. Reflecting galvanometer, Thomson's, 390, 3i2, 404, 406. Register thermometers, 108. , Removal of atmospheric pressure hastens evaporation, 183. Refraction of 'ight, 251. Refractory substances, 121. Refrangibility of heat, alteration in, 74. of light, alteration in, 259. Retardation of telegraphic signals, 402. Ritchie's improved Kuhmkorff's coil, 460. Ruhmkorff's coil, induction coil, 454. mechanical effects of, 464. physiological effects, 464. heating effects, 464. 1 luminous effects, 467. chemical effects of, 475. dissected, 454. decomposition of steam by, 476. conversion of carbon into diamond, 477. Rumford's experiments, on heat of friction, 242. experiments on conducting power of materials used for clothing, 29. Rubidium, 269. S. SALTS, effect of, in lowering freezing point, effects of, in raising boiling point. 134. Sand battery, 398. SAU 549 THE Saussure's hygrometer, 1?9. Saxton's magneto-electric machine, 480. Secondary induced currents of electricity, 423. " decomposition by the battery, 355. Sheathing of ships, how protected, 366. Siemens' magneto-electric macliiue, 496. Sirius, spectrum of. 275. Smee's battery, 337. Sodium, spectrum of, 270. Solar light, effect of, on plants, 278. " "' " ou chemical compounds, 279. Solids, peculiar properties of, 4. Solidification evolves heat, 117. " of carbonic acid, 196. Sources of heat, 232. Spark obtained from magnet, 441. Specific heat, 210. " " determined by mixture, 211. " " determined by rate of cooling, 213. " " determined by time, 212. " - alteration of den- sity,^. " " of solids, 216. " " of liquids, 216. " " of water, 216. " " of gases, 217. Spectra of the Nebulae crossed by bright lines, 235, 276. of Potassium, Sodium, Caesium, and Rubidium, compared with Fraun- hofer's linos. 270. of artificial light and colored flames. 282. projection of, on screen, 265. Spectroscope, 268. Spectrum-analysis, 266. " '' made by Ruhmkorff's coil, 473. Spheroidal state, 160. Stars, spectra of, 2 5. Statham's fuse, 466. Steam, latent heat of. 130. " elastic force of, 133. " used expansively , 155. " temperature of, at different press- ures, 156. " electricity of, 306. " engine, the invention of, by Watt, 141. " condensation of, in condenser, its invention described by Watt, 179. " engine, condensing .and r.on con- densing, how distinguished, 142. " super heated, 158. Still, for distillation, 164. Submarine telegraphic cables, 4r3. Sulphate of copper battery, 332. T. TABLZ of conducting power for heat, 27. conducting power for heat compared with conducting power for electri- city, 28. of Mclloui, showing the amount of heat from different sources, transmitted by different substances, 60. of Melioni, showing the amount of heat from the s; me source that is trans- mitted by different substances, 3. showing the different temperature of the rays of heat of different rofran- gibility contained in the solar spec- trum, 69. of relative expansion of different sol- ids, 82. of Regnault, showing the pressure of steam at different temperatures, 156. of Regnault, showing the sum of sensi- ble and latent heat in steam at differ- ent temperatures, 157. of Regnault, showing the elastic force of watery vapor at different temper atures, 177. of density of vapors at the boiling points of their liquids, compared with that of air, 18U. of temperatures at which different gases solidify, 199. of specific heat of solids of equal weight between 32 and 211, 21o. of specific heat of liquids, 217. of Delaroche and Eerard, of specific heat of gases, 218. of Reguault, of specific heat of gases-, 219. of rise of specific heat with rise of tem- perature, Jil. of heat produced by various combusti- bles, 234. of electro-negative and electro-positive bodies, 351. of magnetic and dia-magnetic bodies, 375. of Morse's telegraphic alphabet, 392. of velocity of telegraphic current, 401. of direction of induced currents up to the ninth order, 4fe8. comparative cost of light, 517. Transfer of solids in voltaic arc, 3i5. Tangent galvanometer, 3i9. Telegraph, magnetic, 387. Telgraphic batteries, 396. " manipulator, 392. " relay , 393. Temperature, increase of, with increase of depth beneath the surface, 233. Thallium, 269. Thomson's reflecting galvanometer, 405. Thermo-chrosis, or calorific tint, 72. " electric battery, 512. " electricity, 510. " multiplier of Melloni, 614. Thermometers, 100. " Breguet's metallic, 110. THE 550 WOL Thermometers, Fahrenheit, 105. <" Centigrade, 106. " Keaumur, 106. *' maximum and minimum, 109. Rutherford's self-register- ing, 109. " comparison of various scales of, 107. " graduation of, 105. " tests of accuracy of, 105. Torpedo, 513- Transmission of heat, 57. ' of telegraphic messages, 395. Triple character of solar light, 260. U. URANIUM glass, 468. V. VALVES of steam-engine, 153. Vaporization, 123. "Vapor, amount of, in the air, 188. " in the atmosphere, affects its bulk and density, 180. Vapors differ in latent heat, 130. Velocity of telegraphic current, 401. Vibrations, number of, required for differ- ent colors, 2uQ. Volta r the inven or of the voltaic pile, 314. Volta's theory. 313. Voltaic pile, 314. " " theory of, 315. Volta-electric induction, 423. " magueto-eleetric induction, 442 Voltameter, 362. W ATER, decomposed by a p ization and transfer, 851. rocess of polar- expansion of, iu cooling, 97. freezing of, in red-hot capsule, 164. frozen by its own evaporation , 183. specific heat of, 216. evolution of heat of, in freezing, 117. maximum density of, 96. expansion of, in freezing, 98. Weight of great importance in chemistry, 14. (496. Wheatstone's magneto-electric machine, Wilde's magneto-electric machine, 489. Wollaston's Cryophorus, 1*5. " Hvpsometer, 133, " Steam-bulb, 140. SCIENTIFIC BOOKS PUBLISHED BY 23 Murray St. and 27 Warren St., NEW YORK. URE'S DICTIONARY of Arts, Manufactures and Mines, sixth edition, greatly enlarged, edited by Robert Hunt, F. R. S. 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