IKKX BER K BLEY LIBRARY UNIVERSITY OF CALIFORNIA THE TWO OCEANS. (i) Aerial Ocean. (2) Greatest height attained by Messrs. Glaisher and Coxwell, being 36,960 feet, or seven miles above the sea level. (3) Aerial Alps, or stratum of clouds 15,000 feet in depth. (4) Highest bird-region. WEATHER WARNINGS WATCHERS BY " THE CLEEK " HIMSELF. WITH CONCISE TABLES FOR CALCULATING HEIGHTS " The actuating force of every wind that blows ; of every mighty current that streams through ocean depths; the motive cause of cyery particle of vapour in the air, of every mist and cloud aiid raindrop, is SOLAS RADIATION." George Warington. LONDON HOULSTON AND SONS PATERX03TER SQUARE, E.G. 1877 [The right of translation is reserved. Altered at Stationers' Hall. ] LIST OP WORKS OF REFERENCE. BOUTAN ET D' ALMEIDA. Cours Elementaire de Physique. BUCHAN,A. Introductory Text-book of Meteorology. W. Black- wood and Sons, 1871. CAZIN, ACHILLE. La Chaleur. HacJiette and Co., 1868. CRAMPTON, REV. Jos., M.A. The Three Heavens. W. Hunt and Co., 1876. CHAMBERS' Encyclopedia. W. and R. Chambers, 1875. DREW, JOHN. Practical Meteorology. Van Voorst, 1870. FITZROY, THE LATE ADMIRAL. Weather Book and Barometer Manual. FLAMMARION, CAMILLE. L' Atmosphere. GUILLEMIN AMEDEE. Les Forces de la Nature. GLAISHER, J., F.R.S. Hygrometrical Tables. Taylor and Francis, 1869. HARTLEY, W. N. Air and its Eelations to Life. Longmans, 1875. HERSCHEL, SIR JOHN F. W. Meteorology, from Eiicy. Brit. A. and C. Slack, 1860. KAEMTZ, L. F. Complete Course of Meteorology. Bailliere London. MARTIN'S Natural Philosophy. Simphin, Marshall and Co., 1868. TYNDALL, JOHN, D.C.L., &c. Heat, a Mode of Motion. Fifth Edition. Longmans, 1875. RODVELL. Dictionary of Science. E. Moxon and Co., 1871. PROCTOR. Science Byways. Smith, Elder and Co., 1875. SCOTT, R. H., M.A.,F.R.S. Instructions in the Use of Meteoro- logical Instruments, 1875. WARINGTON, GEORGE. Phenomena of Radiation. v/y- CONTENTS. PAGE Actinometer ... 10 JEthrioscope ... 16 Altitude tables ... 37 Anemograph ... 84 Anemometers, velocity . 80 Aneroid barometer . . 35 Atmidometer ... 25 Atmospheric electricity . 89 Barograph .... 38 Barometer precautions . 40 description of . 29 construction of . 26 self-recording . 36 warnings . . 43 syphon . . 30 wheel . . 33 corrections of . 27 Beaufort's scale of wind force 76 weather notation . 82 Black bulb in vacuo . . 12 Boiling-point thermometer . 36 Calorification ... 8 Condensation ... 45 Capacity, correction . . 27 Capillarity, correction . . 28 Centigrade thermometer . 20 Cirro-cumulus cloud . . 56 Cirro-stratus cloud . . ' 56 Cirrus cloud ... 52 Clouds, forms of . . 52 amount of 57 Compass bearings . . 71 Conversion of thermometer scales 23 Cumulo-stratus cloud . . 56 Cumulus cloud ... 53 Dew-point .... 48 Electrification ... 86 Electrometers, forms of . 90 Electroscope. ... 89 Evaporation, measurement of 24 Fahrenheit's thermometer . 20 Fortin's barometer . . 27 Freezing-point ... 20 Frost, management of hygromete in 50 Gold-leaf electroscope . . 89 Glass, storm ... 41 Heights, measurement of . 37 Hours of observation . . 39 Howard's cloud nomenclature 52 Hygrometer, Daniell's . 47 PAGE Hygrometer, Mason's . . .48 Hygrometer precautions . . 50 ELew verification . . . .42 Lightning 90 ,, conductors . . .91 Mean sea-level . . . .28 Maximum thermometers . .16 Meteorology, list of works on . 4 Minimum thermometers . .17 Mountain barometers . . .35 Motion 67 Nimbus clouds, form of .57 Ozone, determination of . .91 Ozonometer . . . .92 Packing barometers . . .32 Position of barometers . . .33 Pyrheliometer .... 9 Pressure anemometer . . .79 Psychrometer . . .49 Eadiation, solar ... 9 Radio-solar thermometer . . 13 Rain, measurement of . . .60 Rain gauges . . .62 to 67 Rarefaction 26 Reaumur's scale . . . .20 Regnault's hygrometer . . 47 Robinson's anemometer . . 81 Solar radiation .... 9 Six's thermometer . . .18 Standard barometer . . .28 Stevenson's thermo-screen . . 51 Stratus cloud . . . .55 Suspension of barometers . . 40 Sympiesometer . . . .41 Temperature, correction for . 27 Terrestrial radiation . . .13 Thermographs . . . .23 Thermometer scales . . .20 screens . , .50 radiation . 11, 14 standard . .21 True bearings of wind direction . 71 Vernier, principle of . . .30 setting the ... 31 Weather warnings 40, 44, 53, 54, 55, 56, 57, 58, 59, 60, 73, 77, 94 Wet and dry bulb hygrometer . 50 Wind, registration of . . .85 gauges . . . .79 scales . . . 76, 83 vane . . 78 M372416 PREFACE. THE late Admiral Fitzroy entertained the opinion that the various phenomena which go to form what we call " weather" are " measurable at any place, and that having these measurements at various places over a given area, such as the British Isles, we ought to be able to foresee the peculiar results as regards the direction and force of air currents which have their distinctive weather characteristics in relation to tem- perature, rainfall, and electrical manifestations." A conviction of the soundness of this opinion has induced the writer to make the present compilation, in the hope that many who have hitherto avoided the subject of meteorology and the weather may find interesting matter, where before all seemed dull and technical. Any attempt at rigid mathematical accuracy is disclaimed at the out- set ; the leading principles involved in weather forecasting and storm prevision will, however, be stated in a sufficiently definite manner to divest the subject of the mystery in which it has hitherto seemed to be enshrined, and thus enable the unscientific reader to become weather- wise, and casual observers to note weather phenomena with some degree of method and precision. On page 4 will be found a list of works which have proved useful aids in making _ the present compilation. The writer desires to acknowledge his indebtedness to the various authors and publishers, and especially to Mr. Strachan, for permission to quote from his able pamphlet on "Weather Forecasts, and Storm Prevision," and to repro- duce the valuable table on page 37, for Calculating Heights of Mountains, from the fourth edition of his handy " Pocket Meteorological Eegister." The publication of Weather Reports in the daily journals must have convinced the most indifferent that much greater importance is now attached to weather phenomena than formerly ; and this conviction will be deepened when it is remembered that a Parliamentary grant of 10,000 is annually expended in support of the Meteorological Office and its seven fully organized observatories in this country, while America expends no less a sum than 80,000 annually in the pursuit of weather wisdom ; and the leading nations of Europe have also established meteorological observatories in suitable localities. The balloon ascents of Messrs. Glaisher and Coxwell attracted much attention to the instruments used in estimating atmospheric phenomena, and awakened a desire to know something of the functions of a baro- meter, Thermometer, hygrometer, &c., and especially of the classifi- cation of those important weather- warners, clouds. These subjects will be found duly noted in their order, and every phenomenon being traced to its source, Solar Radiation, it is hoped that these pages may prove generally acceptable, and be deemed not altogether unworthy of "THE CLERK OP THE WEATHER," WEATHER WARNINGS. THE two great Forces of Nature are Gravitation and Heat, which always act in opposition to each other. WEATHER is the result of the action of these forces on matter, and where one form of force is in excess of another, changes are produced which become apparent to our senses, or are indicated by suitable instruments. THE MATTER composing the earth on which we live is of three kinds solid, liquid, and gaseous. THE FORCE incessantly acting on these is the radiant heat of the sun. THE EESULTS of this incessant action are : 1. CALORIFICATION, or Heating, which, besides being appreciable by our senses, is indicated by the THERMOMETER. 2. EVAPORATION, which alters the weight of the air indirectly, by the diffusion of aqueous vapour through it. This alteration of weight is indicated by the BAROMETER, the accom- panying increase of moisture being indicated by the HYGROMETER. 3. EAREFACTION, which alters the weight of the air directly. 4. CONDENSATION, producing fog, dew, rain, hail, and snow ; all sufficiently apparent when they occur, but estimated accurately only by the Eain Gauge, or PLUVIOMETER. 5. MOTION, producing winds, which we are able to appreciate in the gentle breeze and the awful cyclone, the force and velocity of which are indicated by the ANEMOMETER. 6. ELECTRIFICATION, producing lightning, thunder, magnetic phenomena, and chemical change, respectively indicated by the ELECTROMETER, MAGNETOMETER, and OZONOMETER. WEATHER WARNINGS. I.-CALOBIFICATION. Before considering in detail these results of the action of solar radiation on our globe, an attempt to realize the immensity of this stupendous force will materially aid in the general comprehension of the subject. The earth is a sphere somewhat less than 8,000 miles in diameter ; and if we assume, with the gifted author * of " The Phenomena of Kadiation," " that it is about 91,300,000 miles from the sun, and moves around it in a slightly elliptical orbit, occupying rather more than 365 days ; that its shape is globular, somewhat flattened at its two extremities ; that it rotates upon its own axis in the space of 24 hours, that axis being inclined to the annual orbit at an angle of 23 J if we further assume that solar radiation is of such kind and quantity as it is, we are enabled to account for the total amount of light and heat the earth receives, for the superior temperature and illumination of equatorial regions, as compared with polar, with the gradations of intermediate zones, for the alternation of day and night, and the annual pro- gression of the seasons. " The actuating force of every wind that blows ; of every mighty current that streams through ocean depths ; the motive cause of every particle of vapour in the air of every mist and cloud and raindrop, is SOLAR EADIATION. " The delicate tremor of the sun's surface particles, shot hither through thirty million leagues of fine intan- gible sether, has power to raise whole oceans from their beds, and pour them down again upon the earth. We are apt to measure solar heat merely by the sensation it produces on our skin, and think it small and weak accordingly ; a good coal fire will heat us more. But its true measure is the work it does. Judged by this standard, its immensity is overpowering. To take a single instance : the average fall of dew in England is about five inches annually ; for the evaporation of the vapour necessary to produce this trifling depth of moisture, * George Warington, F.C.S. WEATHER WARNINGS. there is expended daily an amount of heat equal to the combustion of sixty-eight tons of coal for every square mile of surface, or, for the whole of England, 4,000,000 tons. Compare now the size of England with that of the whole earth only ^uVsth P ar ^ ; extend the calcula- tion to rain, as well as dew, the average fall of which on the whole earth is estimated at five feet annually, or twelve times greater ; and then estimate the sum of 4,000,000 x 3,388 x 12 = 162,624,000,000 tons, or about 3,000 times as much as is annually raised in the whole world ; and we have the number of tons of coal required to produce the heat expended by the sun merely in raising vapour from the sea to give us rain during a single day/ SOLAR RA.DIATIOX. Seeing, then, that solar radiation plays so important a part in the production of the natural phenomena classed under the head of Meteorology, a description of the mode of estimating its amount will prove in- teresting, and enable the reader to realize the existence of this mighty power. M. Pouillet devised for this purpose the apparatus known as the PYRHELIO- METER, which registers the power of parallel solar rays by the amount of heat imparted to a disc of a given diameter in a given time. It consists of a flat circular vessel of steel A having its outside coated with lamp-black B. A short steel tube is attached to the side opposite to that covered with lamp- black, and the vessel is filled with mer- cury. A registering thermometer C, pro- tected by a brass tube D, is then attached, and the whole is inverted and exposed to the sun, as shown at Fig. 1. The purpose of the second disc, E, is to aid in so placing the apparatus that it shall receive direct paraUel rays. It is ob- vious that if the shadow of the upper about 10 WEATHER WARNINGS. disc completely covers the lower one, the sun's rays must be perpendicular to its blackened surface. "The surface on which the sun's rays here fall is known ; the quantity of mercury within the cylinder is also known ; hence we can express the effect of the sun's heat upon a given area by stating that it is competent, in five minutes, to raise so much mercury so many degrees in temperature." * Sir John Herschel also designed an instru- ment for observing the heating power of the sun's rays in a given time, to which the title Acti- nometer is given. It consists of a Thermometer with a long open scale and a large cylindrical bulb, thus combining the best conditions for extreme sensibility. An observation is made by exposing the instrument in the shade for one minute and noting the temperature. It is then exposed to the sun's rays for one minute, and a record of the temperature made. It is again placed in the shade for one minute, and the mean of the two shade readings being deducted from the solar reading shows the heating power of the sun's rays for one minute of time. The stimulus imparted to the study of this class of phenomena by the publications of Pro- fessor Tyndall's researches on Eadiant Heat has induced a demand among Meteorologists for instruments capable of yielding more available indications than those just described. This demand has been most efficiently supplied by the ingenuity of scientists and instrument \ makers. Tcti The earl 7 form of Solar Radiation Ther- nometer. mometer was a self-registering maximum thermometer, with blackened bulb, having its *' graduated stem, only, enclosed in an outer tube. Errors arising from terrestrial radiation and the * Tvndall, "Heat a Mode of Motion." WEATHER WARNINGS. 11 Improved Solar .Radiation Thermometer in Vacuo. Scale about g. variable cooling influences of aerial currents are all obviated in the improved and patented Solar Kadiation Thermometer shown at Fig. 3, which consists of a self- registering maximum thermometer, having its ~bvXb and stem dull-blackened, in accordance with the sugges- tion of the Eev. F. W. Stow, and the whole enclosed in an outer chamber of glass, from which the air has been completely exhausted. The perfection of the vacuum in the enclosing chamber is proved by the production of a pale white phosphorescent light, with faint stratification and transverse bands when tested by the spark from a Euhmkorff coil. Due provision is made for this by the attachment of platinum wires to the lower side of the tube, and when tested by a syphon pressure gauge, the vacua have been proved to exist to within 1-5 Oth of an inch of pressure. It will thus be seen that the indications are preserved from errors arising from atmospheric currents, and from the ab- sorption of heat by aqueous or other vapours, the whole of the solar heat passing through the vacuum direct to the blackened bulb. The contained mercury expanding, carries the recording index to the highest point, and thus is obtained a registration of the maximum amount of solar radiation during the twenty-four hours. The great advantage accruing from the high degree of perfection to which this instrument has been brought is, uniformity of con- struction, which renders the observations made at 12 WEATHER WARNINGS. different stations intcrcomparaUe. An enlarged view of the thermometer is given at Fig. 3, showing the platinum wire terminations, whereby the vacuum is tested. The Eev. Fenwick W. Stow thus directs the manner in which the solar radiation thermometer should be used : 1. Place the instrument four feet above the ground, in an open space, Fig. 4, with its bulb directed towards the S.E. It is necessary that the globular part of the external glass should not be placed in contact with or very near to any substance, but that the air should circulate round it freely. Thus placed, its readings will be affected only by direct sunshine and by the temperature of the air. 2. One of the most convenient ways of fixing the instrument will be to allow its stem to fit into and rest upon two wooden collars fastened across the ends of a narrow slip of board, which Solar Radiation -Thermo- j s na n e d in its centre upon a post meter, black bulb and stem TIT i t \ in vacuo, on 4 feet stand, steadied by lateral supports Scale about & (Fig. 4). 3. The maximum temperature of the air in shade should be taken by a thermometer placed on a stand in an open situation. Any stand which thoroughly screens it from the sun, and exposes it to a free circu- lation of air, will do for the purpose. 4. The difference between the maxima in sun and shade, thus taken, is a measure of the amount of solar radiation. The remarkable phenomenon recently discovered by Mr. Crookes, in which light is apparently converted into motion, has, at the suggestion of Mr. Strachan, WEATHER WARNINGS. 13 5. Radio- Solar Thermometer. Scale about \. received an interesting application to meteorology. The arrangement is shown at Fig. 5, where a Solar Kadi- ation Thermometer has a Crookes' Kadiometer attached to it, which, in addition to forming an efficient test as to the perfection of the vacuum, will, it is hoped, aid in eventually establishing a relation between intensity of radiation, as shown by the thermometer, and the num- ber of revolutions of the radiometer. The instrument has so recently been devised that any positive statement as to its usefulness would be premature; it may, however, prove a valuable auxiliary to the solar thermo- meter, and eventually be so far improved as to become a more definite exponent of solar radiation than the thermometer. TERRESTRIAL RADIATION. It is an established fact, confirmed by careful experi- ments, that a mutual interchange of heat is constantly going on between all bodies freely exposed to view of each other, thus tending to establish a state of equilibrium. It has further been ascertained that, as the mean temperature of the earth remains unchanged, " it necessarily follows that it emits by radiation from and through the surface of its atmosphere, on an average, 14 WEATHER WARNINGS. the exact amount of heat it receives from the sun." This process commences slowly at sunset, and proceeds with great rapidity at and after midnight, attaining its maximum effect in a long night, in perfect calm, under a cloudless sky, resulting in the condensation of vapour in the form of dew, or hoar-frost, when the temperature of the surface-air is reduced to the dew-point.* The extent to which heat thus escapes by radiation under varying conditions of sky is measured by a Self-registering Terrestrial Minimum Thermometer, the bulb of which is placed over short grass, and "a thermometer so exposed un- . cler a clear sky always marks severar degrees below the tem- perature of the Terrestrial Radiation Thermometer, air, and its de- Scale about . pression affords a rude measure of the facility for the escape of heat afforded under the circumstances of exposure." f Fig. 6 shows the ordinary spherical bulb thermometer employed for this purpose, and Fig. 7 the improved Cylinder Jacket Thermometer, which, by exposing a larger surface of spirit to the air, gives an instru- ment possessing an amount of sensi- bility in no way inferior to that of mercury. There is a draw- Improved Cylinder Jacket Terrestrial Minimum ^ ck t0 t] ? e USe Thermometer. Scale about ^. 01 these thermo- * See page 47. t Herscbel. WEATHER WARNINGS. 15 meters enclosed in outer tubes, arising from moisture getting into the outer cylinder or jacket, and frequently preventing the observer from reading the thermometer. This has recently been removed by making a perfectly ground joint of glass (analogous to a glass stopper in a bottle) as a substitute for the old form of packing at the open end of the tube, the other end being fused into con- tact with the outer cylinder to keep it in its place. The intrusion and condensation of moisture thus becomes impossible, while the scale is protected from corrosion or abrasion. This "ground socket" arrangement is shown at Fig. 8. Ground Socket Minimum Thermometer. Scale about |. Eadiation from the earth upwards proceeds with great rapidity under a cloudless sky, but a passing cloud, or the presence even of invisible aqueous vapour in the air, is sufficient to effect a marked retardation, as is beautifully illustrated by Sir John Leslie's ^Ethrio- scope, shown at Fig. 9, which consists of a vertical glass tube, having a bore so fine that a little coloured liquid is supported in it by the mere force of cohesion. Each end of the tube terminates in a glass bulb containing air. A scale, having its zero in the middle, is attached to the tube, and the bulb A is enclosed in a highly polished sphere of brass. The upper bulb B is blackened, and placed in the centre of a highly-gilt and polished metallic cup, having a movable cover F. These outer metallic coverings protect the bulbs from extraneous sources of 16 WEATHER WARNINGS. "JEtbrioscope. Scale about f . heat. So long as the upper bulb is covered, the liquid in the tube stands at zero on the scale, but immediately on its removal radiation commences, the air contained in B contracts, while the elasticity of that contained in A forces the liquid up the tube to a height directly proportionate to the rapidity of the radiation. SHADE TEMPERATURE. Self-registering Maximum Thermo- meters are made in two ways. In the first, the index is a small portion of the mercurial column separated from it by a minute air bubble. The noontide heat expands the mercury, Self- registering Maximum Thermometer. Scale about -. and the subsequent contraction as the temperature de- creases affects only that portion of the mercury in con- nection with the bulb, leaving the disconnected portion to register the maximum temperature. In the second form the tube is ingeniously contracted just outside the bulb, so that the mercury extruded from the bulb by expansion cannot return by the mere force of cohesion, but remains to register the highest temperature. There is a modification of this latter form produced by the addition of a supplementary chamber just outside the bulb and over the column, from which, as expansion proceeds, the mercury flows by gravitation, but into which it cannot return until, as in the other forms, the instrument is readjusted for a new observation, by WEATHER WARNINGS. 17 unhooking the bulb end and lowering it until the mercury Hows into its place. Self-registering Minimum Thermometer. Scale about i. Self-registering Minimum Thermometers are of two kinds, spirit and mercurial. Fig. 12 shows one of Ruther- ford's Alcohol Mini- mum Thermometers, Self- registering Minimum Thermometer. which will be seen to Scale about 1- consist of a bulb aud tube attached to a scale, which latter may be either of wood, glass, or metal. The tube contains an index of black glass. The Thermometer is " set " for observation by slightly raising the bulb end until the index slides to the extreme end of the column of spirit. It is then suspended in the shade with the bulb end a little lower than the other. The contraction of the spirit consequent on a fall of temperature draws the index back, but a subse- quent expansion does not carry it forward, it remains at the lowest point to which the spirit has contracted to register the minimum temperature. A very useful modification of this instrument is made for gardeners and general horticultural purposes, in which the scale is of cast zinc with raised figures, which being iUed off flush after the whole has been painted of a dark colour are easily legible at a little distance. The advantage of alcohol for the indication of very low temperatures is that it has never been frozen;* Fig. 13 shows a set of Maximum and Minimum and Wet and Dry Bulb Thermometers, with incorrodible Mvixury freezes at-3UF. j; WEATHER WARNINGS. Standard Set of Instruments on Screen. Scale about J-. porcelain scales, suspended on a mahogany screen. Instruments of this quality are generally engine-divided on the stem, and if, in addition to this, they are verified by comparison with standard instruments at the Kew Observatory, they may be regarded as standards, and employed for accurate scientific observations. Six's Self-registering Thermometer consists of a long tubular bulb, united to a smaller tube more than twice its length, and bent twice, like a syphon, so that the larger tube is in the centre, while the smaller one terminates at the top, on the right hand, in a pear-shaped bulb, as shown in the cut (Fig. 14). This bulb, and the tube in connection with it, are partly filled with spirit ; the long central bulb and its connecting tube are com- pletely filled, while the lower portion of the syphon is filled with mercury. A steel index, prevented from falling by a hair tied round it, to act as a spring, moves in the spirit in each of the side tubes. The scale on the left hand has the zero at the top, and that on the right WEATHER WARNINGS. 1U at the bottom. When setting the in- strument, the indices are brought into contact with the mercury by passing a small magnet down the outside of each tube. Then, should a rise of temperature take place, the spirit in the central bulb expands, forcing down the mercury in the left hand tube and causing it to rise in the right, and vice versa for a diminution of temperature. It should be always used and carried upright, and the indices should be drawn gently down by the magnet into contact with the mercury; and, when a reading is taken, the ends of the in- dices nearest the mercury indicate the maximum and minimum temperatures which have been attained during the stated hours of ob- servation. Six's form of ther- mometer has been extensively used for ascertaining deep sea temperatures. Evaporation and , the mechanical action of winds keep up a constant circulating motion of the ocean, the currents of which tend to equalize temperature. The most im- portant of these is known as the Gulf Stream, taking its name from the Gulf of Mexico, out of which it flows at a velocity sometimes of five miles an hour, and in a width of not less than fifty miles. It has an important effect and "Minimum Regis- on the climate of Great Britain, and of lands sllb J ect to its influence, its 14 Six's Thermometer. Scale about f . Deep Sea Maximum 20 WEATHEK WARNINGS. loo temperature as it leaves the Gulf of Mexico being 85 F., diminishing to 75 off the coast of Labrador, and still further as it nears northern latitudes. Observations on the temperature of the ocean are therefore included in the scope of meteorology, and are ascertained by the use of thermometers of special construction (Fig. 15). In the earlier experiments made for ascertaining the temperature of the ocean at a depth of 15,000 feet, where the pressure is equal to three tons on the square inch, it was found that a considerable error occurred in the indications in consequence of this enormous pressure; accordingly the central elongated bulb of the ordinary Six's Thermometer (see page 19) is shortened and enclosed in an outer bulb nearly filled with spirit, which, while effectually relieving the ther- mometer bulb from undue pressure, allows any change to be at once trans- mitted to it, and thus secures the regis- tration of the exact temperature. The arrangement possesses the further ad- vantage of making the instrument stronger, more compact, and more capable of resisting such comparatively rough treatment as it would receive on board ship. The honour of constructing the first thermometer, which was an Air and Spirit Thermometer, is ascribed to Galileo ; it assumed a practical shape in 1620, at the hands of Drebel, a Dutch physician. HalJey substituted mercury for spirit in 1697; Reaumur improved the instrument in 1730, and Fahrenheit in 1749. More recently the instrument has been perfected by the scales being graduated on the actual stem of the instrument. For 16. Comparison of Ther mometer Scales. Scale about $. WEATHER WARNINGS. 21 many years it was exclusively used by chemists and men of science ; it afterwards received numerous ap- plications in the arts and manufactures; and is now considered an essential in every household. Thermometers are instruments for measuring tem- perature by the contraction or expansion of fluids in enclosed tubes. The tubes, which are of glass, have spherical, cylindrical, or spiral bulbs blown on to one end ; they have also an exceedingly fine bore, and when mercury or spirit is enclosed in them these fluids, in contracting and expanding with variations of tempera- ture, indicate degrees of heat in relation to two fixed points viz., the freezing and boiling points of water. Care is taken to exclude all air before sealing, so that the upper portion of the tube inside shall be a perfect vacuum, and thus offer no resistance to the free expansion of the mercury. In graduating, or dividing the scales, the points at which the mercury re- mains stationary in melting ice and boiling water are first marked on the stem, and the intervening space divided into as many equal parts as are necessary to constitute the scales of Fahrenheit, Reaumur, or Celsius, the last being known as the Centigrade (hun- dred steps) scale, from the circumstance of the space between the freezing and boiling points of water being divided into one hun- dred equal parts (Fig. 16). GRADUATION or THERMOMETERS. When the fluid (either mercury or spirit) has been enclosed in the hermetically sealed tube, it becomes necessary, in order that its indica- tions may be comparable with those of other instruments, that a scale having at least two fixed points should be attached to it. As it has been found that the temperature of "Legible 1 melting ice or freezing water is always cal ^g t h e " n constant, the height at which the fluid rests Scale about 22 WEATHER WARNINGS gj&D -100 -5 ;30 80 70 60 40 Gridiron-bulb Thermome- ter. Scale about 1 . in a mixture of ice and water has been chosen as one point from which to graduate the scale. It has been also found that with the barometer at 29 '905 the boiling-point of water is also constant, and when a thermo- meter is immersed in pure distilled water heated to ebullition, the point at which the mercury remains immovable is, like the freezing-point, carefully marked, the tube is then calibrated and divided as shown in Fig. 16. The zero of the scales of Reaumur and Centigrade is the freezing-point of water, marked, in each case, 0, while the inter- vening space, up to the boiling-point of water, is divided, in the former case, into 80 parts, and in the latter to 100. In the Fahrenheit scale, the freezing-point is represented at 32, and the boiling-point at 212, the intervening space being divided into 180, which admits of extension above and below the points named, a good thermo- meter being available for temperature up to 620 Fahr. The use of the Reaumur scale is con- fined almost exclusively to Russia and the north of Germany, while the Centigrade scale is used throughout the rest of Europe. The Fahrenheit scale is confined to England and her colonies, and to the United States of America. Circumstances sometimes arise in which it becomes necessary to convert readings from one scale into those of the others, ac- cording to the following rules : 1. To convert Centigrade degrees into degrees of Fahrenheit, multiply by 9, divide the product by 5, and add 32. WEATHER WARNINGS. 23 19. Thermograph and Self-recording Hygrointter. Scale about T V 2. To convert Fahrenheit degrees into degrees of Centigrade, subtract 32, multiply by 5, aud divide by 9. 3. To convert Eeaumur degrees into degrees of Fahrenheit, multiply by 9, divide by 4, and add 32 * 4. To convert Eeaumur degrees into degrees of Centigrade, multiply by 5 and divide by 4.f For the production of continuous records, the Meteoro- logical Committee of the Eoyal Society have adopted an instrument called a Thermograph, or self-recording wet and dry bulb thermometer, which is largely aided by photography. The bulbs of the thermometers are necessarily placed in the open air, and at a suitable distance from any wall or other radiating surface ; the tubes are of sufficient length to admit of their being brought inside the building, in due proximity to the recording apparatus placed in a chamber from which daylight is rigidly excluded. S R = IS F. t 8 R = 10 f. 24 WEATHETJ WARNINGS. The essential conditions in such an apparatus are:- - 1. A means of denoting the height of the mercurial column in the stem of a thermometer in relation to a fixed horizontal line. 2. A time scale denoting the exact moment at which the atmosphere reached the temperature indicated by the mark. 3. As the marks are produced chemically, and not mechanically (as in the Anemograph), a dark room. A description of the drawing on page 23 will best show how very efficiently, through the ingenuity of Mr. BECKLEY, these conditions have been obtained : S, wet bulb thermometer; T, atmospheric thermometer; B, screw for adjusting thermometers ; C C, paraffin lamps or gaslights ; D D, condensers, concentrating the light on the mirrors RE; E E, mirrors reflecting light through air-speck in thermometers V V ; E E, slits through which light passes from mirrors E E ; F F, photographic lenses, producing image of air-speck from both thermometers on cylinder G; G, revolving cylinder or drum carrying photographic paper; H, clock, turning cylinder G round once in 48 hours ; I, shutter to intercept light four minutes every two hours; leaving white time-line on developing latent image. II.-.EVAPOKATION. Solar heat rarefies the air by driving its particles asunder; it also vaporises water from the surface of river, lake, and ocean, diffusing the vapour through the atmosphere. Great interest attaches to the subject of Evaporation, on account of its connection with rainfall and water supply. It is to be regretted, therefore, that the results hitherto obtained in the endeavour to measure its rate and quantity do not merit much confidence as regards their applicability to the evaporation occurring in nature, owing to the exceptional manner in which the obser- vations have been made. There is this uncertainty about evaporation, that all WE.YTHEll WAKXLXGS. the experiments relate to that taking place from an exposed water surface of a, comparatively speaking, in- linitesirnally small area, and can therefore have but a very partial applicability to the conditions occurring in nature. There are two main reasons for this statement. Firstly, the proportion of the surface of the land on the earth which is covered with lakes and rivers is very limited, and the experiments above indicated throw no lighten the evaporation from the soil. Secondly, the evaporation from the surface of a small atmometer erected on the ground, with comparatively dry air all around it, is certainly very different from that which would take place from an equal area in the centre of a large water sur- face, such as a lake. It is of course easy to make ex- periments on the evaporation from the soil by means of a balance atmometer, but in order that these should possess a practical value, the investigation must be extended so as to include a wide variety of soils, &c., &c. As re- gards the second point which has been raised, it is recommended by the Vienna Congress to erect at- mo meters in the centre of water surfaces ; but it is not a very easy matter to conduct such experi- ments with accuracy, owing to the risk of in-splashing from waves. BABINGTON'S ATMIDOMETER measures evaporation from water, ice, or snow, and in form resembles a hydrometer, with the difference that the stem bears a scale graduated to 26 WEATHER WARNINGS. grains and half grains, and is surmounted by a light, shallow copper pan. When in use, the hydrometer- like instrument is immersed in a glass vessel having a hole in the cover, through which the stem protrudes. The copper pan is then placed on the top, and sufficient water, ice, or snow placed therein to sink the stem to the zero of the scale. As the evapo- ration proceeds, the stem rises ; and, if the time of commencing the experiment is noted, the rate as well as the amount of evaporation is indicated in grains. III.-BAKEFACTION. The diffusion of aqueous vapour through the air and the rarefying influence of heat jointly effect an alteration in the weight of the atmosphere. This alteration of weight is determined by the Barometer, an instrument invented by TORRICELLI, in 1643, and in so perfect a form that in its essential features it has not been superseded. The mode of con- struction is illus- trated by Figs. 21 and 22. It consists in hermetically sealing a glass tube about three feet long and filling it with mer- cury. The ringer is placed over the open end of the tube, which is then invert- ed and placed in a cistern of mercury and the finger with- drawn. The left- hand figure shows the result ; the mer- Constmctionof Baro. CUrV is S6en to / a11 Construct^ of Baro- meter. Scale about ,V Some three or lour meter. Scale about f s . WEATHER WARNINGS. 27 inches, leaving an empty space at the top of the tube, which is called the " Torricellian vacuum." The mercury is prevented from falling lower than is shown, by the external pressure of the atmosphere on the cistern. The v;eiglit of this column, therefore, represents the weight or pressure of a corresponding column of air many miles in height; and so close is the relation between the column of mercury and the external air that the height of the former changes with the slightest variation in the weight of the latter, and the instrument thus becomes a measure of the weight of the air, from which property its name is derived, the Greek words laws and metron signifying respectively " weight " and " measure." When the mercury in the barometer tube falls, that in the cistern rises in corresponding proportion, and vice versa, so that there is an ever-varying relation between the level of the mercury in the tube and the mercury in the cistern, which affects the accuracy of the readings. In M. Fortin's cistern this diffi- culty is obviated by. the use of a glass, with flexible leather bottom and a brass adjusting screw, as shown in the cut. Through the top of the cistern is inserted a small ivory point, the lower end of which corresponds with the zero of the scale ; and, to secure uniformity, the level of the mercury in the cistern should 23. be adjusted by the screw at each observation, Fortiu's until the ivory point appears to touch its own g ca fe aj^t reflection on the surface. The reading is . then taken. In making barometric observations for comparison with others, it is necessary that all should be reduced to the common temperature of 32 R, and for this purpose tables have been calculated which will be found to save much time. Tables also for reducing observations of the barometer to sea level, an operation equally indispensable with the WEATHER WARNINGS. other corrections to make the readings intercomparable, have been published by direction of the Meteorological Committee. Tor the British Isles the mean sea-level at Liverpool has been selected by the Ordnance Survey as their datum, and the height of any station may be ascertained by first noting the nearest Ord- nance Bench Mark thus ^ ,and purchasing that portion of the Ordnance map which includes the station, near to which the Bench Mark will be found with the height above sea- Capillarity, level duly entered. The level- Scale about {,. lings made for railways will also furnish the desired information. Failing both these, the observer should select two or more of the stations nearest his locality for which official Meteoro- logical Eeports are published daily in the Times and other journals ; and taking observations of his barometer at 8 a.m., for a few weeks, should compare them with the mean of the observations at those stations. The comparison should be omitted when the barometer pressure is not steady. A Standard Barometer is constructed on FORTIN'S principle, and should have its tube about half an inch bore, enclosed in a brass body having at its upper end two vertical openings, in which the vernier works. The mercury is seen through these openings, aided by light reflected from a white opaque glass reflector let into the mahogany board WEATHER WARNINGS. 29 behind. The scale is divided on one side into English inches and 20ths, and may have on the other French millimetres, the vernier enabling a reading to be taken, in each case re- spectively, of l-500th of an inch and l-10th of a millimetre. In making the instrument, the mercury is boiled in the tu be, to ensure the complete exclusion of air and moisture; while FORTIN'S principle of cistern ensures a constant level from whence to take the readings. A sensitive thermometer with scale, engine-divided on stem, is at- tached to the brass mount, which is perforated to ad- mit the attenuated bulb of the thermometer into absolute contact with the glass tube of the barometer, to ensure its indicating the same temperature as the con- tained mercury. The instrument is suspended by a ring from a brass bracket attached to a mahogany board, and the lower end passes through a larger ring having three screws for adjusting it vertically. A "reading "is taken in the following manner : 1. Xote the temperature by the attached thermometer. 2. Raise or lower the mercury in the cistern by turning the screw underneath until the reflected image of the ivory point on the mercury seems to be in contact with the ivory itself. By the milled head at the side, the vernier is adjusted until its lower edge just touches the top of the mercurial column, the scale and vernier then indicate the height of the barometer in inches, lOths, lOOths, and lOOOths. High-class instruments, such as that here described, yield exc/cf readings ; but, in order to note them ac- curately, it is important that the eye, the zero edge of the vernier, the top of the mercurial column, and the back of the vernier should be in the same horizontal plane ; conditions which may be obtained after some practice. The accompanying illustration shows a form of barometer which, though not much used in this country, is deservedly popular on the Continent as a standard station barometer. It is called a Syphon Barometer, and was designed by Gay-Lussac. The WEATHEE WAKNINCB. open end of the tube is bent up in the form of a syphon, the short limb being from six to eight inches long ; it is furnished with metal scales and verniers, and is mounted on a mahogany board with attached thermo- meter. These barometers require no correction for capillarity or capacity, each surface of mercury being equally depressed by capillary attraction, and the quantity of mercury falling from the long limb occupies the same space in the short limb. The usual cor- rection for temperature must, however, be applied. A scale of inches, measured from a xero point taken near the bend of the tube, furnishes the means of measuring the long and short columns. The difference of readings is the height of the barometer. Tie VERNIER is a movable scale for sub- dividing parts of a fixed scale, and was first applied to that purpose by its inventor, M. PIEKEE VERNIER, in 1630. In the barometer the parts to be divided are inches, which by the aid of this invention are subdivided into lOths, lOOths, and lOOOths. Fig. 27 shows the scale of a standard barometer divided into ^-lOths, or '05 of an inch. The Vernier C D is made equal to 24 of such divisions, and is divided into 25 equal parts, from whence it follows that one division on the scale is l-25th of '05 larger than one on the vernier, so that it shows a difference of '002 of an inch. The vernier reads from '0, or zero, upwards ; D, there- Barometer. fore, indicates the top of the mercurial column. In Fig. 27, zero on the vernier is exactly in line with 29 inches and 5-10ths of the fixed scale; the reading, therefore, is 29'500-inches. The vernier 26. Syphon WEATHER WAIIXIXCIS. 31 line a falls short of a division of the scale by '002- inch ; b, by '004 ; c, by -006 ; d, by "008 ; and the succeeding line by '010. If the vernier be adjusted to make a coincide with z on the scale, it will have moved through '002 - inch ; and if 1 on the ver- nier be moved to co- incide with y on the scale, the space mea- sured will be "010- inch. Consequently, the figures 1, 2, 3, 4, 5, on the vernier, measure lOOths, and the intermediate lines even lOOOths of an inch. In Fig. 28 the zero of the vernier is 27. between 29 '6 5 and The Vernier. 29'70 on the scale. Glancing up the vernier and scale, the second line above 3 will be found in a direct line with one on the scale : this gives '03 and '004 to add to 29*65, so that the actual reading is 29'684. In those instances where no line on the vernier is found precisely to coincide with a line on the scale, and doubt arises as to which to select from two equally coincident lines, the rule is to take the intermediate 1000th of an inch. For household and marine barometers such minute subdivisions of the scale are unnecessary, and the scales of such instruments are therefore divided only to lOths, and the verniers made only to read to 1 OOths of an inch, which is effected by making the vernier 9-10ths or ll-10ths of an inch long, and dividing it into 10 equal parts. 28. The Vernier. 32 WEATHER WARNINGS. n In " taking a reading " it is important that it should be done as quickly as possible, as the heat from the body and the hand is sufficient to interfere with that accuracy which is necessary where the intention is to compare the readings with those made by other observers. This facility is soon acquired by a little practice. Pediment Household Barometers, though not so imposing in appearance as the Wheel Barometer, yield direct readings without the intervention of the mechanical appliances necessary for moving a needle over an extended dial. Their mountings are for the most part in oak, walnut, and other woods, the scales are of ivory, porcelain, or enamelled glass, and in their graduation due regard is paid to the relative pro- portions of cistern and tube, so that the conditions essential to the pro- duction of a Standard Barometer arc very closely attained. In common with other barometers, it should hang in the shade in a vertical position, so that light may be seen through the tube. As a purchaser would receive it in what is called a " portable " state, it will be necessary on first suspending it to take the pinion key, fit it on the square- headed pin at the bottom of the instru- ment, and turn gently to the left till the screw stops. The effect of this is to lower the base of the cistern, and allow the mercury in the tube to fall to its proper level. The key should then be replaced for use in moving the vernier. To make this kind of Barometer portable for WEATHER WARNINGS. travelling it should be un- hung, very gradually sloped until the mercury is at the top of the tube, when, the instrument being upside down, the base of the cistern is screwed up by turning the pinion key gently to the right until it stops. Care should be taken to avoid concussion, and to have the cistern end always upper- most, or the instrument lying flat. Tig. 2 9 shows a useful form of barometer for the farmer, combining as it does three instruments in one, for the thermometer on the right hand of the scale having its bulb covered with muslin kept moist by communica- tion with a cistern of water enables the two thermo- meters to be employed as a Hygrometer, the use of which is described at page 50. This barometer should be suspended in a place where it will be exposed as much as possible to the ex- ternal air, but not in sun- shine. In Wheel Barometers the varying height of a column of mercury is shown by the movement of a needle on a divided circular dial, by adopting the syphon form of Wheel Barometer. Scale about I. WEATHER WARNINGS. barometer tube, concealed behind the dial and frame. An iron or glass float sustained by the mercury in the open branch (Fig. 31) is suspended by a counterbalance a little lighter than itself. The axis of the pulley has the needle attached to it, and consequently moves the needle with the rise and fall of the mercury. It is obvious, therefore, that if the atmospheric pressure increases the float falls and the needle turns to the right, and if it diminishes the needle turns in the opposite direction. The divisions on the scale represent inches, tenths, and hundred ths in the rise and fall of a column of mercury, and these can be read with great facility, as one inch occupies the space of six or more on this very open scale, according to size of dial (Fig. 30). The wording is arbitrary, and indicates the pro- bable weather that may be ex- pected. Important improvements have recently been effected in this form of household barometers, so that they may be recommended as good weather indicators where fa- cility of reading is a desideratum. Since the more scientific " Pedi- ment" has attained so high a degree of popularity, a certain amount of unmerited obloquy has attached itself to the Dial or Wheel Barometer invented by Dr. Hook. It must be conceded that the stand- ard form of pediment barometers in which the height of the mercury is seen at a glance is more strictly an " instrument of precision/' but it should not be forgotten, although Mechanism of Wheel a d e ii cate mechanism intervenes Barometer. ., j ,v Scale about |. between the mercury and the WEATHER WAR N IXC S . 35 observer, it is so arranged that a tenth of an inch rise or fall causes a movement of the index over an inch of space. The Aneroid Barometer indicates variations in at- mospheric pressure by the elevation and depression of the sides of an elastic metallic box from which the air is exhausted and which is kept from complete collapse by a powerful spring. In cases where extreme accuracy is not indis- pensable, the porta- bility and sensibility of this instrument recommend it for use by tourists and fisher- men. It is " quick in showing the varia- tions of atmospheric pressure."* "The Aneroid readings may be safely depended upon."f " Its move- ments are always con- sistent."} " Atmo- spheric changes are indicated first by the Aneroid." It 13 Aneroid Barometer. Fall size. especially adapted for determining mountain altitudes, some being furnished with a scale of feet, enabling the observer to read off the height by direct observation, and if adjusted once a year by comparison with a mer- curial standard is quite trustworthy. It is fully described in a small pamphlet entitled " The Aneroid Barometer : How to Buy, and How to Use it," by a Fellow of the Meteorological Society. * Admiral Fitzroy. t James Glaisher, Esq., F.R.S. James Belville, Esq., Royal Observatory, Greenwich. Sir Leopold McClintock. " 36 WEATHER WARNINGS. By a suitable arrangement of clockwork, revolving a cylinder bearing prepared paper, the aneroid barometer forms an admirable self-recording instrument, showing at a glance the height of the barometer : whether it is falling or rising, for how long it has been doing so, and at what rate the change is taking place, whether at the rate of l-10th per hour, or l-10th in twenty-four hours facts which can only be obtained by very frequent and regular observations from an ordinary barometer, but which are nevertheless essential to a reliable " weather forecast."* The height of mountains may also be determined by the temperature at which water boils, as this depends on the pressure of the atmosphere, and according to fDeschanel, "just as we can determine the boiling - point of water when the external pressure is given, so if the boiling-point be known we can determine the external pres- sure," and as this varies with the eleva- tion above sea-level, the boiling-point of water also varies. These facts induced Wollaston to attempt the determination of heights of mountains by an apparatus which he called the Barometric Thermometer, subsequently modified by Eegnault and called a Hypsometer, but now more generally known as a Boiling-point Thermometer. A portable form of boiling-point thermometer is shown at Fig. 33, which is much used by Alpine travel- lers, and forms a trustworthy check on the aneroid and barometer. 33. Boiling-point Thermometer. Scale about ^. * The Aneroid Barometer : How to Bmj mid How to Use it. By a Fellow of the Meteorological Society. Post free for six stamps, from any bookseller or optician. WEATHER WARNINGS. 37 COKCISE TABLES FOR CALCULATING HEIGHTS BY MEATS OF BABOMETER OB AKEBIOD, AKD ALSO BY THE BOILIHG-POIHT THERMOMETER. 213-78 212-13 210-43 208-67 206-87 205-01 203-09 201-11 199-05 196-92 BAEOMETEK AT UPPER STATION. INCHES. 859 873; 889 905 921 939 888; 904 920 937 955 .. 919 936 953 971 988 1007 1028 102711048 21 977J 998 1020 1043 1068 1095 1124 1155 1188 " 10871115114411761210 994 1015 10381062 1012 1033 10561081 . 952 970 9891009102810511075J1100 1050107310971122 10701093 1118 1145 1069 1092 1116 11411169 1198 1229 1262 1299 1338 1115 1140 11661194 1224 1256 1290 1327 1367 , r TjT-T 1164 11911220 1251 1284 1319 1358 1399 -un. a ictr. | ioi Q lio< al2 80 1314 1350 1390 1433 10 70 1278 19 IS 17 ID 15 11071135116511981233 1271156118712201257 1150 1180 1211 1246 1283 1173 1203 1236 1271 1309 3101346138314241469 _ ... 1343 1380 1419 1461 1507 ...1416145715001548 0-973 1-018 1-040 1-062 1-084 1-127 Factor A 1497 1542 1592 15881639 RULE I. If the temperature of boiling water be observed at either or both Stations, find the equivalent pressure in the 2nd column, and calculate the height as for barometer. RULE II. The readings of the Barometer being corrected and reduced to 32 a F., multiply the difference of pressure between the Stations by factor A, found in line with pressure at lower Station, and under that at upper Station ; multiply again by factor B, corresponding to the mean temperature of the air at the Station ; apply as many times C as there are thousand feet in the height, corresponding to the latitude ; and add D, the correction for gravity. EXAMPLE. At the top of Snowdon, lat. 53 N., an aneroiJ read 26'48, correction 0-18, the pressure at sea-level was 29'91 : the temperature of the intermediate air was 57 e ; find the heignt. Lower Station 29-91 inches. Upper 26-30 Factor A Factor B 3-61 933 1083 1083 3249 3368 1.055 16840 16840 3368 (neglecting decimals.) N.B. In taking out the quantities, if accuracy is aimed at, it will be necessary to proportion for parts in the usual manner with such Tables. 3553 Cor. C=3xl = -3 Cor. D +10 Height 3560 feet. 3$ WEATHER WARNINGS. The illustration (Fig. 33) shows the instrument with the telescopic tube drawn out for use, and the thermo- meter surrounded by the vapour of boiling water. The lamp is protected from wind by a perforated japanned tin case covered with wire gauze. When the boiler is charged and the lamp ignited the mercury ascends, and the point at which it becomes stationary shows Barograph. Scale about the temperature, which will give the elevation in feet above the sea-level on reference to the table supplied by the optician from whom the instrument is purchased. A highly-refined automatic arrangement is adopted at some observatories called a Barograph, which, by the aid of photography, becomes a self-recording mercurial barometer. It is simpler in its arrangement than the WEATHER WARNINGS. 39 thermograph, and includes a clock of superior construc- tion, causing a cylinder bearing photographic paper to make one complete revolution in forty- eight hours. A double combination of achromatic lenses brings to a focus rays passing through a slit placed in front of the mercurial column, behind which is a strong gaslight or paraffin lamp, the rays of which are condensed up<_ n the slit by a combination of two plano-convex lenses. Although a barometer is an instrument artificially constructed by man, it should not be forgotten that when once made the column of mercury is placed in a passive or quiescent state in direct relation with the great forces of nature, so that its indications become to some extent natural phenomena. This is aptly illustrated by what is called the " daily fluctuation " of the barometer which occurs in all countries, though the hours and extent vary with the latitude, diminishing as the latitude increases, according to a definite law. The phenomena does not admit of a satisfactory explanation, but is doubtless connected with the daily variations of temperature and of vapour in the air. The mercury falls naturally (so to speak) from nine or ten to between three and four p.m. ; it then rises till between nine and ten p m. It falls again about four a.m., and rises again about ten a.m. It is usually highest at nine a.m. and nine p.m., and lowest at three a.m. and three p.m. These natural elevations and depressions of the mer- cury should be allowed for in reading the barometer, as any rise or fall in opposition to the natural rise and fall possesses for that reason increased importance. For instance, fine weather may be expected if the mercury rises between nine a.m. and three p.m. ; in like manner rain may be expected should a fall take place between three p.m. and nine p.m. It will be inferred from the preceding facts that there are certain hours better suited for "taking a reading" than others. When one observation only is made daily, noon is the best time, two observations should be made at nine a.m. and nine p.m., and for three the best hours 40 WEATHER WARNINGS. are nine a.m. (maximum), noon (mean), and three p.m. (minimum). The opinion generally entertained that a high baro- meter is an indication of fine weather, and a low one a warning of bad weather, is open to exception, and an increased value would attach to the indications of the instrument in proportion as the following points are noted and allowed for : 1. The actual height of the mercury. 2. Whether it is rising or falling. 3. The rate of rise and fall. 4. Whether the rise or fall has been long continued. The state of the barometer foretells coming weather, and when the present weather disagrees with the baro- meter a change will soon take place. A fall of half a tenth, or more, in an hour is a sure warning of a storm, a rapid rise is a warning of unsettled weather. The barometer is generally lowest with wind from the S.W., and highest with wind N.E., or with a calm. N.E. and S.W. may be called the wind's poles, and the difference of height due to direction only from one of these bearings to another amounts to about half an inch. BAROMETER PRECAUTIONS. If vacuum suspected, cause mercury to strike top of tube. A clear metallic " click " indicates a good vacuum. 4 dull " thud " indicates air or moisture. In latter case return to optician, but if unable Incline very gently until nearly inverted, when Air if present will ascend in a bubble into the cistern. Suspend barometer in good light out of sunshine. Let no heat of fire or lamp affect it. Let no sudden changes of temperature affect it. It must hang absolutely vertically. Note temperature of attached thermometer before reading barometer. Then adjust mercury in cistern to touch ivory point. Then adjust vernier and take reading quickly. Ascertain height above sea-level according to direction. The Storm Glass (Fig. 36) is a glass bottle, ten inches long, containing a mixture of camphor, nitre, sal-ammoniac, alcohol, and water. As l( temperature affects the mixture WEATHER WARNINGS. 41 35. 36. Storm Glass, or Chemical Weather Glass. 37. Scale about much," an arrangement has recently been designed in which the stem of a thermometer is immersed in the fluid, as shown at Fig. 37, thus imparting a higher value to its indications. The late Admiral Fitzroy says "Since 1825, we have generally had some of these glasses, as curiosities rather than otherwise ; for nothing certain could be made of their variations until lately, when it was fairly demonstrated that if fixed undisturbed in free air, net exposed to radiation, fire, or sun, but in the ordinary light of a well- ventilated room, or, preferably, in the outer air, the chemical mixture in a so-called storm glass varies in character with the direction of the wind not its force." The quarter from which the wind or storm is blowing is indicated by the substance adhering more closely to the bottom of the glass opposite to the point whence the wind or tempest arises. The Sympiesometer is an instrument used chiefly at sea for purposes of comparison with the mercurial and aneroid barometers. Its indications result partly from the pressure and partly from the temperature of the atmosphere ; it would, therefore, be more correctly named a Thermo-Barometer. 42 WEATHER WARNINGS. The height of the atmosphere has been variously estimated : By Bravais, from the duration of twilight, at 66 to nearly 100 miles; by Dalton, in 1819, from observations of the auroral light, at 102 miles; by Sir John Herschel, from similar observations in 1861, at 83 miles; from observations of meteors, from 100 to 200 miles; by Liais, in 1859, from observations on the polarisation of the sky, at noless than 212 miles. The density of the atmosphere diminishes with dis- tance from the earth's surface, in accordance with the following rule : "At a height of seven miles the density of the atmosphere is reduced to one-fourth the density at the sea-level, and for every additional seven miles, the rarity of the air is similarly quadrupled." NOTE ON THE VERIFICATION OF INSTRUMENTS AT THE KEW OBSERVATORY. The Kew Committee of the Boyal Society receive, for verification and comparison with the standard instru- ments of the Kew Observatory, barometers, thermo- meters, and other instruments intended for meteorological observation or scientific investigations. Any persons ordering instruments of opticians may direct them to be previously forwarded to the observa- tory for verification. A scale of charges is issued by the Committee which is exclusive of packing and carriage, or of rail expenses, when a special messenger is sent out. The Meteoro- logical Office, Victoria Street, London, also receives and forwards instruments for verification to the Kew Observatory. The Committee wish it to be understood that they cannot undertake the verification of an interior class of instruments (such as barometers mounted upon wooden frames, and thermometers not graduated on the stem), and that the superintendent of the observatory may at his discretion decline to receive such instruments as he may consider unfit for scientific observation. WEATHER WARNINGS. 43 t>^ S-fS*^^ t llll|lllll.s ua:S^o+H=oo s - 1 ^- t> o^ ^^.S g.S^ 1 ^- ii** ^lIliT^ 1 o< a z "^ rt ^ ^^ l^le&slijs A>*1 44 WEATHER WARNINGS. EXPLANATOEY CARD. BY THE LATE VICE-ADMIRAL FITZROY, F.R.S., ETC. WEATHER GLASSES. THE BAROMETER RISES for Northerly wind (including from North-west, by the North, to the Eastward), for dry, or less wet weather, for less wind, or for more than one of these changes : EXCEPT on a few occasions when rain, hail, or snow comes from the Northward with strong wind. THE BAROMETER FALLS for Southerly wind (including from South-east, by the South, to the Westward), for wet weather, for stronger wind, or for more than one of these changes : EXCEPT on a few occasions when moderate wind with rain (or snow) conies from the Northward. For change of wind toward Northerly directions, A THERMOMETER FALLS. For change of wind toward Southerly directions, A THERMOMETER RISES. Moisture or dampness in the air (shown by a Hygrometer) increases BEFORE rain, fog, or dew. On barometer scales the following contractions may be useful : RISE FALL FOR FOR NORTH SOUTH N.W. N. E. S.E. 8. W. DRY WET OR OR LESS MORE WIND. WIND. EXCEPT EXCEPT WET FROM WET FROM NORTH. NORTH. Add one-tenth of an inch to the observed height for each hundred feet the Barometer is above the half-tide level. The average height of the Baro- meter, in England, at the sea- level, is about 29-94 inches; and the average temperature of air is nearly 50 degrees (London lati- tude). The Thermometer falls about one degree for each three hundred feet of elevation from the ground, but varies with wind. "When the wind shifts against the sun, Trust it not, for back it will run." First rise after very low Indicates a stronger blow. Long foretold long last, Short notice soon past. (In South Latitude read South for North.) WEATHER WARNINGS. 45 IV.-CONDENSATION. Dew is a deposition of moisture from the air, resulting from the condensation of the aqueous vapour of the atmosphere on substances which have become cooled by the radiation of their heat. This is, in fact, the sub- stance of Dr. Wells's famous Theory of Dew, enunciated in 1814, and which, according to Dr. Tyndall, " has stood the test of all subsequent criticism, and is now uni- versally accepted," and by which all the phenomena of dew may be explained. Dr. Wells's experiments were interesting and conclu- sive. He exposed definite weights (10 grains) of wool to the air on clear nights, one on a four-legged stool, the other under it, the upper portion gained 14 grains in weight, the lower only 4 grains. On an evening when one portion of wool, protected by a curved pasteboard roof, gained only 2 grains, a similar portion on the top of the miniature roof gained 16 grains. A little re- flection will suggest the explanation : radiation from the wool was arrested by the pasteboard cover, while the por- tion fully exposed to the sky lost all its heat, and thus condensation ensued. Dr. Wells speaks with such candour, and so pointedly, on this fact and its consequences, that his words may be advantageously quoted : " I had often, in the pride of half-knowledge, smiled at the means frequently employed by gardeners to protect tender plants from cold, as it appeared to me impossible that a thin mat, or any such flimsy substance, could prevent them from attaining the temperature of the atmosphere, by which alone I thought them liable to be injured. But when I had learned that bodies on the surface of the earth become during a still and serene night colder than the atmosphere, by radiating their heat to the heavens, I perceived immediately a just reason for the practice I had before deemed useless." Familiar instances of the formation of dew will have been noted by many " watchers ; " e. 1 "02 1 . |2 HH 1 S t . ^ . y- ^ V -v ' p PQ dpj! O t-l 0 1 '3 a W pq S S -! 1 2 d -g 2 ^ ^ 02 : Moderate G -1 o ^ 1 1 o bt 02 ) Whole Gale 1 02 Hurricane 1 . CQ to O >o i i S 5 ^ s o o o oo o Oi jad spunod s 9 >0 O O Ut e-rassajj o o r ~ l * ^t 1 ^o c^ co I I tO o co cb co if O to O to to to o tO tO o i; O O r-H 11 82 WEATHER WARNINGS. 0, the next reading will, of course, show the number of miles the wind has traversed; but, should they stand otherwise, the reading may be noted and deducted from the second reading, thus : Suppose the fixed index points to 2-5 and the movable index to 125, the reading after 12 hours may be 200 on the outer circle and 3'0 on the inner circle : these added together yield 203. By deducting the previous reading 127'5, we have the true reading viz., 75 '5 miles as the distance travelled by the wind. Having obtained the velocity of the wind in this manner in miles per hour, the table on page 83, from Col. Sir Henry James's "Instructions for Taking Meteorological Observations," will enable the observer to calculate the pressure in pounds per square foot. WEATHER NOTATION. The following letters are used to denote the state of the weather : b denotes blue sky, whether with clear or slightly hazy atmosphere. c ,, cloudy, that is detached opening clouds. d , , drizzling rain. / fog- h ,, hail. / lightning. in misty, or hazy so as to interrupt the vie\v. o overcast, gloomy, dull. p passing showers. q squally. r , rain. snow. thunder. ugly, threatening appearance of sky. unusual visibility of distant objects. wet, that is dew. A letter repeated denotes much, as rr, heavy rain ; /; dense fog ; and a figure attached denotes duration in hours, as 14r, 14 hours' rain. By the combination of these letters all the ordinary phenomena of the weather may be recorded with certainty and brevity. Examples. be, blue sky with less proportion of cloud ; cb, more cloudy than clear; Irrllty heavy rain for two hours, with much light- ning, and some thunder. WEATHER WARNINGS. 83 VELOCITY AND PBESSURE OF THE WIND. The Pressure varies as the Square of the Velocity, or P oc The Square of the Velocity in Miles per Hour multiplied by -500 gives the Pressure in Ibs. per square Foot, or F 2 x -005 P. The Square Root of 200 times the Pressure equals the Velocity, or V 200 x P = F The subjoined Table is calculated from this data, by COL. SIR HENRY JAMES, of the Ordnance Survey Office. ' " " " 1 5 | .3 ,: g | -S a | 9 c a | .9 c s *l .2 v- 8.5*1 >* to 3 5 fe * o * ll^ '81 s^Pn >> o<^ * o 1*1 P 7. |l| |8g 111 1*2 ill P" III Ps gc> 8. > 34 02 t> & * S > * S oz. Ibs. Ibs. Ibs. Ibs. e-os i-ooo 6-75 36-742 17-75 59 581 28-75 75-828 39-75 89162 0-25 1-767 7-00 37'4l5 1800 60-000 29-00 76-157 40-00 89-442 n-50 2-500 7-25 38-078 18-25 60-415 29-25 76-485 40-25 89-721 0-75 3-061 7-50 38-729 1850 6U-827 29-50 76-811 4050 90-000 1-00 3-535 7-75 39-370 18-75 61-237 29-75 77136 4075 90-277 1 2-00 5-000 8-00 40-000 19-00 61-644 30-00 77-459 41-00 90-553 3-00 6-123 8-25 40-620 19-25 62048 3025 77-781 41-25 90-829 4-00 7-071 8-50 41-231 19-50 62-449 30-50 78-102 41-50 91-104 5-00 7-905 8'75 41-833 19-75 62-819 30-75 78*421 41-75 91-378 6-00 8-660 9-00 i 4-2-426 20-00 63-245 31-00 78-740 42'00 91-651 7-00 9-354 9 25 ! 43-011 20-25 63639 31-25 79*056 42-25 91-923 8-00 10-000 9-50 43-588 20-50 64-031 31 -50 79-372 42-50 92-195 !-00 10-606 9-75 44-158 20-75 64-420 31-75 7968>i 42-75 92-466 10-00 11-180 10-00 44-721 21-00 64807 32-00 80-000 43-00 92-736 11-00 11-726 10-25 45-276 21-25 65-192 3-2-25 80-311 43-25 93-005 12-00 12247 1050 1 45825 2150 65-574 32-5'.' 80-622 4350 93-273 13-00 12-747 10-75 46-363 21-75 65-954 32-75 80-932 4o *75 93-541 14-00 13-228 11-00 46-934 22-00 66-332 33-00 ; 81-240 44-00 93-808 15-00 IS'693 11-25 47-434 22-25 1 66-708 33-2-5 ! 81-547 44-25 94-074 11-50 47-958 22'50 67-082 33-50 81-853 4450 94-339 Ibs. 11-75 48-476 22-75 67 453 33-75 82158 4475 94-604 1-00 14-142 12-00 48-989 23-00 67-823 34-00 ' 82-462 15-00 94-868 1-25 15-811 1225 49-497 23-25 68-190 3425 ! 82-764 45-26 95-393 I'oO ' 17-320 12-50 50-000 2350 68-556 34-50 83-066 45-50 95-131 1-75 i 18-708 1275 50-497 23-75 68-920 3475 83*366 45-75 95-655 2-00 20-000 13-00 50'990 24'flO 69-282 35-00 83-666 46-00 95-916 225 21-213 13*26 51-478 24*29 69-641 3525 83964 46-25 96-176 2-50 22-360 13-50 51-961 24-50 70-000 35-50 84-261 46-50 96436 2'75 23-452 1375 52-440 24-75 70-356 3575 84-567 46-75 96-695 300 2f494 14-00 52-915 25-00 70-710 3600 84-852 47-00 96-953 3 25 25-495 14-25 53385 25-25 71-063 36-25 85146 47-25 97-211 3-50 26457 14-50 53 851 25'50 71-414 36-50 85-440 47-50 97-467 3-75 27-386 14-75 54-313 25-75 71-763 36-75 85-732 47-75 97724 4-00 ! 28-284 lo'OO 54-772 26-00 72-111 3700 86.023 48-00 97-979 4-25 29-154 15-25 55 226 26-25 7-2-456 37-25 86-313 48-25 98-234 4-50 30-000 15-50 55-677 26-50 72-801 3/-50 86-602 48-50 98488 4-75 30-822 15'75 56-124 26-75 73143 37-75 86-890 48-75 98-742 5-00 31-622 16*00 56568 27-00 73-484 38-00 87-177 49-00 98-994 5-25 32-403 16-23 i 57-008 27"25 73-824 38-25 ! 87-464 49-25 99-247 5-50 33-166 16-50 1 57-445 27-50 74-161 38-50 87-749 49-50 99-498 5-75 33-911 16-75 57-879 27'7o 74-498 38-75 88 034 49-75 99-749 6-00 34-641 17-00 58-309 28-00 ; 74-833 39-00 88317 50-00 100-000 6-25 35-355 17-25 58-736 28-25 ! 75-166 39-25 88-600 6-50 ! 36-055 17-50 59-160 28-50 75-498 39-50 88-881 84 WEATHER WARNINGS. This is the only table hitherto much in use for con- verting velocity into pressure, and was prepared by Smeaton and others. It does not, however, express the true relation, which has yet to be determined. The Anemograph, or Self-Recording Wind Gauge, has for its object the registration of the velocity and clirec- Anem^graph. Scale about ^. Portion for exterior of observatory. tion of the wind from day to day. Pigs. 59 and 60 show the form designed and arranged by Mr. Beckley, of the Kew Observatory, which has been adopted by the Meteorological Office. It consists of a set of hemispherical cups and vanes, which ^ are exposed on the roof of the house, and of the recording apparatus, which is placed inside the house. WEATHER WARNINGS. 85 The motion imparted to the hemispherical cups by the wind is communicated to the steel shaft B, which, passing through the hollow shaft C, and having at its lower end an endless screw, works into a series of wheels in the iron box D, which reduces the angular velocity 7,000 times. At the required distance the motion, having emerged at E, is connected with F, where, by means of bevelled wheels, it moves the spiral brass registering pencil C, which is arranged so that each revolution records 50 miles of velocity on the prepared paper H. The direction of the wind is indicated by the arrow L, Anemograph. Scale about -$. Portion for interior of observatory. which is kept in position by the fans M. These com- municate, by an endless screw and train of wheel?, through the shaft C and the box D to the recording apparatus, consisting of a spiral brass pencil, which in one revolution records variations through the cardinal points of the compass, on the same prepared paper as that which receives the record of velocity. The paper is held on the drum by two small clips, and may be readily changed, by unclamping the cross V, without disturbing the drum or any other part of the instrument. 86 AVEATHER WAENINGS. Self-recording Magnetometer, Kew Observatory. VI.-ELECTRIFICATION. William Gilbert, a physician of Colchester, first showed in 1600 that the earth as a whole has the properties of a magnet, and consequently that the directive action exerted by it upon a compass needle represents only a special case of the mutual action of two magnets. In 1845, Faraday established the fact that susceptibility to magnetic force is not, as was generally believed, confined to iron, nickel, and a few other substances, but is a property of all substances. According to Balfour Stewart, auroras and earth currents may be regarded as secondary currents resulting from changes in the earth's magnetism. Magnetic phenomena are included under the general term terrestrial magnetic elements, and consist of magnetic declination, inclination, and intensity. These are for convenience determined separately ; the first by an instrument called a Declinometer, and the second by an Inclinometer or Dipping Needle. The Decli- nometer is also made to serve the additional purpose of WEATHER WARNINGS. 87 measuring the intensity of the earth's magnetic force, which it effects on a principle similar to that by which the force of gravity is determined by the oscillations of a pendulum of known length on any given portion of the earth's surface. The declinometer needle is made to oscillate, and the number of oscillations in a given time counted ; due allowance being made for the strength of the needle, it is obvious that the force which restores the needle to rest can be estimated. To ascertain the angle of declination, the zero line of the compass card is made to coincide with the geographical north and south line ; and the angle which the direction of the needle makes with this line is then read off on a gra- duated circle over which the needle turns. The magnetic inclination or dip of the needle is estimated by observing the inclination to a horizontal plane of a needle turning on the vertical plane which passes through the magnetic north and south points. Fig. 62 shows a simple form of magnetic needle suspended on a fine steel point, which is supported by a brass stand ; the addition of a graduated circle would constitute such an arrangement a Declino- meter. Fig. 63 gives the appearance of the dipping needle, or Inclinometer, and Fig. 65 an arrange- ment by which both kinds of terrestrial as well as local attrac- tion may be shown. These compo- nents of the earth's magnetism undergo not only an annual but a daily and even hourly variation, ap- parently connected in some occult manner with the frequency of the sun's spots. The needle sometimes suffers such exceptional perturbations as to suggest the 88 WEATHER WARNINGS. idea of a magnetic storm. These disturbances are usually accompanied (in polar regions) by luminous phenomena called aurorse. Continuous automatic records of them, therefore, is of great value, as facilitating inductive re- search which may lead to valuable practical results. Accordingly the Royal Society have adopted for the Kew and other observatories the form of Magnetograph, or Self-recording Magnetometer, shown at Fig. 61, by means of which the variations just referred to are regis- tered by the oscillations of three magnets on photo- graphically prepared paper, stretched on a drum revolved by clockwork. One magnet is suspended in the magnetic meridian by a silk thread, and, by the aid of a mirror attached, it describes on the cylinder, moved by clockwork in the centre pier, all the variations in the magnetic declination. The other two components of the magnetic force of the earth are given by the other magnets. That recording the vertical variations Tests on two agate edges under a glass shade, while the horizontal component magnet is suspended by a double silk thread, under the shade to the right of the picture, being retained by the tension of the thread in a position nearly at right angles to the magnetic meridian. The clock box in the centre covers the three revolving cylinders bearing the sensitive photographic paper, and to each magnet is attached a semicircular mirror, which reflects the rays from a gas jet to one of the cylinders, and thus describes by a curved line the oscillations of the magnet. A second semicircular mirror is fixed to the pier on which the instrument stands, and conse- quently describes a straight line, or zero, from whence the curves are measured. To avoid errors attending sudden changes of tempera- ture, underground vaults are always chosen for magnetic observations, and also on account of light being more easily and perfectly excluded. WEATHER WARNINGS. 89 ATMOSPHERIC ELECTRICITY. Since the performance of Franklin's famous kite experiment, by which he determined the identity of lightning with the electrical discharge from a machine, much attention has been devoted, not only to that form of atmospheric electricity which displays itself in the thunder-cloud, but to the electric condition of the air in all states of the weather. These researches have estab- lished the fact that the air is always in , an electrical condition, even when the sky is clear and free from thunder- clouds. The instruments employed for ascertaining the kind and inten- sity of atmospheric electricity are called Electroscopes. Fig. 65 shows a modification of Saussure's Electro- scope, the basis of which is a narrow- mouthed flint glass bottle with a divided scale to indicate the degree of divergence of the gold leaves or straws. To protect the lower part from rain, it is covered by a metal- lic shield about five inches in diameter. Bohnenberger's Electro- scope indicates the presence and quality of feeble electric currents. Peltier's Electrometer yields the same result by the deflection of a magnetic needle. This latter has been in use at Brussels for thirty years, and at Utrecht for twenty years, and is highly recommended. Singer's Atmospheric Electroscope is an efficient form of the instrument in which an ordinary gold-leaf elec- trometer has attached to its circular brass plate a brass rod two feet in length, with a clip at its upper ex- Electroscope. Scale about f. 90 WEATHER WARNINGS. tremity to receive a lighted paper or cigar fusee. The electricity of the air in immediate contact with the flame, causes, by induction, electricity of the opposite nature to accumulate at the upper extremity, where it is constantly carried off by the convection currents in the flame, leaving the conductor charged with the same kind and power of electricity as that contained in the air at the time of the experiment. The principle of this method was initiated by Volta, and has been extended and applied by Sir William Thomson in his Water-dropping Collector, which consists of an insulated cistern from which water escapes through a jet so fine that it breaks into drops immediately after leaving the nozzle of the tube. The result of this is that in half a minute from the starting of the stream the can is found to be electrified to the same extent as the air at the point of the tube. The scale value of each instrument has to be separately determined by repeated comparative ex- periments, and involves much delicacy of manipulation. It is chiefly important for the ordinary observer to know that the occurrence of thunder and lightning should be always noted in the column headed "Bemarks/' The destructive effects of lightning- are too well known to need description here ; the means, however, by which these may be averted demand a brief notice. Lightning when discharged from a cloud will always choose the better of any two conductors which may present them- selves. The stone of a church steeple and the wood of a ship's mast are bad con- ductors, but a galvanized iron wire rope is the best possible conductor, and ac- cordingly this material is now generally employed for the purpose. A lightning conductor consists of three parts: 1, the Lightning Conductor. Scale about , WEATHER WARNINGS. 91 rod, which extends beyond the summit of the building, 2, the conductor, which connects the rod with the underground portion, and 3, the part underground. The connection between each of these must be ab- solutely perfect, or the conductor will be faulty. The top is usually of solid copper tipped with platinum (Fig. 66), the body of galvanized iron rope, so as to adapt itself to the inequalities of the building and yet have no sharp turns in it, while the part underground is of solid iron rod. This latter portion should extend straight underground for two feet, and being bent at right angles away from the wall, should rest in a horizontal drain 10 to 15 feet long filled with charcoal, and be again bent downwards into a well of water. Should water not be available, it should rest in the centre of a hole 15 feet deep and 10 inches in diameter, tightly packed with charcoal, which, while conducting the electricity from the rod into the earth, serves also to preserve the iron from rusting. OZONE. The atmosphere, besides holding the vapour of water diffused throughout its mass, contains also minute traces of carbonic acid and ammonia, and a very remarkable substance called Ozone. Oxygen, one of the component gases of the atmosphere, is capable of existing in two conditions ; one in which it is comparatively passive, and another in which it possesses exceptional chemical activity, dependent apparently upon its electrical condi- tion, and in which state it possesses a peculiar smell which has caused it to be named ozone.* The charac- teristic odour is always observable near a powerful elec- tric machine when it is being worked, near a batter}' used for the decomposition of water, and in the air after the passage of a flash of lightning. Its presence is most marked near the sea-coast, and in localities remarkable for their salubrity; and on account of its influence on health, it has been proposed by Schonbein and others * Greek ozo, I smell. 92 WEATHER WARNINGS. to include ozonometrical observations with the ordinary meteorological observations. Although in minute quantities it is favourable to health, when existing in undue 'proportion it irritates the mucous membrane of the nose and throat, producing painful sores. It attacks india-rubber, bleaches indigo, and oxidizes silver and mercury, differing in all these points from ordinary atmospheric oxygen. The chemical energy it possesses (which exceeds that of ordinary oxygen as much as the latter exceeds atmospheric air as an oxidizing agent) affords the means of ascertaining its presence and quantity. It liberates iodine from its combination with potassium, and free iodine colours starch a deep blue. Schonbein, the discoverer of ozone, found that when strips of paper previously saturated with starch and iodide of potassium and dried were exposed freely to the air but protected from rain and the direct action of the sim, they underwent a peculiar discoloration (when immersed in water) after an exposure of 24 hours. A scale of tints numbered from one to ten afforded the means of comparative observation, and thus the Ozono- meter was constructed, and a means established of registering the amount of ozone in the air of various localities from day to day. Schonbein also observed that the proportion of ozone was largely augmented after heavy falls of snow. For the exposure of the ozone papers, an ozone cage is employed, as shown at Fig. 67. Ozone may be prepared arti- ficially as a disinfectant by cau- tiously mixing without friction 6? 7 or concussion equal parts of Ozone Cage. peroxide of manganese, per- Scale about $. manganate of potash, and oxalic acid. For a room containing 1,000 cubic feet, two tea- WEATHER WARNINGS. 93 spoonfuls of the powder, placed in a dish and moistened with water occasionally, will develop the ozone and disinfect the surrounding air without producing cough. The most important and interesting series of facts, however, connected with ozone are those established by the researches of M. Houzeau, who states : 1. That country air contains an odorous oxidizing substance, with the power of bleaching blue litmus, without previously reddening it, of destroying bad smells, and of bluing iodized red litmus. 2. That this substance is ozone. o. That the amount of ozone in the air at different times and places is variable, but this is at most ^r^/, of its volume, or 1 volume of ozone /UffjtKXJ in 700,000 of air. 4. That ozone is found much more frequently in the country than in towns. 5. That ozone is in greatest quantity in spring, less in summer, diminishes in autumn, and is least in winter. 6. It is most frequently detected on rainy days, and during great atmospheric disturbances. 7. That atmospheric electricity is apparently the great generator of ozone. The subject is one of great interest in its bearings on health, and opens a wide field of scientific research, as may be inferred from the opinion expressed by the Vienna Congress, which is that " the existing methods of determining the amount of ozone in the atmosphere are insufficient, and the Congress therefore recommends investigations for the discovery of better methods." Mr. Lowe has published the valuable weather warnings tabulated on page 94, which are interest- ing as showing from a given number of observations the value of each phenomenon : 94 WEATHER WARNINGS. No. of _1 Followed in 24 uuserva- tions. hours by Fine. Rain. DEW. SDew profuse Dew from 1st April to 30th Sept. 241 185 196 161 43 24 Dew from 1st Oct. to 30th March 56 37 19 CLOUDS. f White stratus in the valley } Coloured clouds at sunset 229 35 201 26 28 9 (Solar halos ... 204 133 71 Sun red and shorn of rays 34 31 3 SUN. Mock suns 35 19 6 Sun shone through thin cirro- stratus 13 6 7 Sun pale and sparkling 51 27 24 FBOST. White frost ... 73 59 14 1 Lunar halos 102 51 51 Mock moons 9 7 2 MOON. Lunar burr 64 47 17 Moon shining dimly 18 12 6 Moon rose of a red colour 8 7 1 Falling stars abundant ... 85 65 20 STABS Stars bright 83 64 19 Stars dim 54 32 22 Stars scintillated 14 12 2 AUBOBA. Aurora borealis ... 76 49 27 [Bats flying about in the evening 61 45 16 Toads in the evening 17 12 5 Landrails clamorous 14 13 1 Ducks and geese noisy 10 7 3 Spiders hanging on webs in the evening 8 5 3 Fish rise in the lake 15 9 6 SMOKE. Smoke rising perpendicularly . . . 6 5 1 Among the animals whose movements give weather warnings few are more trustworthy than the leech. The reader may verify this by placing one in a broad glass bottle, tied over with perforated leather, or bladder. If placed in a northern aspect, the leech will be found to behave in the following manner : 1. On the approach of fine or frosty weather, accord- ing to the season, it will be found curled up at the bottom. 2. On the approach of rain, snow, or wind, it will rise excitedly to the surface. 3. Thunder will cause it to be much agitated, and to leave the water entirely. WEATHER WARNINGS. 95 PERIODS. M. Koppen states, as the result of his examination into the chances of a change of weather, that the weather has a decided tendency to preserve its character. Thus, at Brussels, if it has rained for nine or ten days successively, the next day will be wet also in four cases out of five ; and the chance of a change decreases with the length, of time for which the weather from which the change is to take place has lasted. In the case of temperature for five-day periods, the same principle holds good ;* for if a cold five-day period sets in after warm weather, we can bet two to one that the next such period will be cold too ; but if the cold has lasted for two months, we can bet nearly eight to one that the first five days of the next month will be cold too. The chance of change is, however, greater for the five-day periods than for single days. Similar results follow for the months, but here again the chance of change shows an increase. " If we revert to the instance first cited, that of rain, the result is, not that if it once begins to rain the chances are in favour of its never ceasing ; all that is implied is, that the chances are against its ceasing on a definite day, and that they increase with the length of time the rain has lasted. The problem is similar to that of human life : the chance of a baby one year old living another year is less than that of a man of thirty. " The practical meaning of all this is, that although we know that a compensating anomaly for all extraor- dinary weather exists somewhere on the earth's surface, c. g., the very common case of intense cold in America, while we have a mild winter in Britain, there is no reason as yet ascertained to anticipate that this compen- sation will occur at any given place during the year. In other words, when definite conditions of weather have thoroughly established themselves, it is only with great difficulty that the courses of the atmospheric currents are changed." * " Recent Progress in Weather Knowledge," by R. II. Scott, F.R.S. 9<> WEATHER WARNINGS. To bring within the limits of a popular pamphlet a notice of the various phenomena classed under the head of Meteorology, it has been necessary to exercise the utmost brevity. Brief, however, as the treatment has been, reference has been made to the sciences of Heat, Light, Electricity, Magnetism, Gravitation, Astronomy, Chemistry, Geography, and Geology, thus corroborating the testimony of Sir John Herschel, who states that " it can hardly be impressed forcibly enough on the attention of the student of nature that there is scarcely any natural phenomenon which can be fully and completely explained in all its circumstances without a union of several perhaps of all the sciences ; and it cannot be doubted that whatever walk of science he may determine to pursue, impossible as it is for a finite capacity to explore all with any chance of success, he will find it illuminated in proportion to the light which he is enabled to throw upon it from surrounding regions. But, independently of this advantage, the glimpse which may thus be obtained of the harmony of Creation, of the unity of its plan, of the theory of the material universe, is one of the most exalted objects of contemplation which can be presented to the faculties of a rational being. In such a general survey he perceives that science is a whole whose source is lost in infinity, and which nothing but the imperfection of our nature obliges us to divide. He feels his nothingness in his attempts to grasp it, and he bows with humility and adoration before that Supreme Intelligence who alone can comprehend it, and who 'in the beginning saw everything that He had made, and behold it was very good.' " J. AMD W, 1UDKB, PRINTERS, LOXDON. FOURTEEN DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. .INN INTERLIBRARY LOAN JAN 7 1976 UNIV. 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