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It touched the wood-bird's folded \\'\n%. And said, "0 bird, awake and eingl" And o'er the farms, " chanticleer. Your clarion blow ; the day is near !" It whispered to the fields of corn, "Bow down, and hail tiie coming morn !" It shouted through the belfry-tower, "Awake, bell! proclaim the hour." It crossed the churchyard with a sigh, And said, " Not yet! in quiet lie." H. W. LOKGFKLLOW . ^ ^) f^ a i ,Vl (S) CEJ^TRIFUGAL FORCE c^ GRAVITATION. Theory of the Nature of Light, The Wave Theory of Sound THE NATURE OF FORCE, AND TH ; MANIFESTATION OF FORCE IN THE PHENO- lENA BELONGING TO PHYSICAL SCIENCE. )IY JOHN HARRIS. Ittotttrcal: PKlNTEl) BY LOVELL PRINTINU AND PDBLISHING CO. St. Nicholas Strbet. June, 1875. ;J-2 3. ^ ->- Ly2> Hz t.i' PEEFATORY NOTE. The particular subject of this boolc is the true nature, in aphysical sense, of Light, anil an examination of certaii; Joc- trinos now taught in respect to it. The doctrine, now al most universally considered as authorized by science, knowi' as the Undulatory Theory of Light is closely allied to the Wave Theory of Sound, upon the analogy to which, indeed, it is ii. a considerable measure based and supported. A part of the objections which wo have to ofl'er to the Undulatory Theory apply also to the Wave Theory of Sound, and it appears therefore desirable to put befor^ the i-eader a brief examina- tion of that important theory also. In order to do tlus without complicating the immediate argument on the sub- 'jcct of Light, the examination of the Wave Theory and observations 'on the nature of Sound will appear as a second division of this book, in which division wo purpose also to supply certain facts from the recoi-d of Physical Science illustrating the arguments and conclusions on the subjects of Light and Souud in their relation to Physical Science. ■:X' ' INDEX FIRST DIVISION. The Nature of Light. page (1) The CorpuHculftr EmifiHioii Tlu-ory fl Objt'Ctioiifl to the Tlieory 10 (2) The Uiidultttory Theory 14 Objections to the Theory 17 Science and Theology 19 Science and Metaphysics 2(j (3) Velocity of Light Theory 31 Objections to tlie Theory 42 Exuniination of liie Record Ilelerence to Experience by instances 49 Light. Suninmry of the Evidence. Conclusion byj ^^ inductive reasoning as to the nature of light . ) (4) Generalization on the Nature of Force fil Force and Matter t)3 Allied Forces of PhyHical Science 65 (0) The relationship of Volumetric Electricity and Light.. fiC The Luminous Train of the Comet 1 Electrical Induction in its application to this \ 79 case ) Evidence of the relationship from the general record 80 SECOND DIVISION. The Matibial Kelations op Force. (1) The Wave Theory of Sound 93 Objections to the theory 102 Examples and Illustrations from the Record 115 • The Nature of Sound 12? / 6 ) INDEX. j» , (2) Muiiili'slutioiiM of tlie various Ibrms (iiioUeH) of Ibrce oil iiiatU'i'. A . — Mu>?iii'lic mill Tlii'iniiil i'IUh-Ih hI" EU'ctricily . . 127 li.— Molfculur (Voltuic) l-lli'ctricity, iiiul llii' Ma-) I 132 ti-riul Kli'iiioiilH ut' cuiii|)ouiul iiiulUr ) C— Culoric-Forcu ami Miiltor 13tf D.— MiifiiietiHiii ami Mii;,'iic'ti>-KU'Ctric Force 142 K. — Ma};iieti/.atioii of Li;;lil aiul Dia-Miij^iit'tiHiii.. 14U (;i) 'i'lie MuU-rial World and llii' Uiiiviisi' 157 Conclusion ItiO APPENDIX. (1) IIcr.scliel'H ili'Hcriiitioii of tilt" Eclipsi's aiul Ucciilta- j i,... tioiiH ol Jujiilcr'H Mulcllilt's ) (2) TvinlaH'H Olisi'rvalioiis on the lillior of tin- Unilula-i lory theory J '*'^ (3) Appendix to the Allied Manilestutioiis of Force on matter. «.— Ma<;neto-Klectric Force 1 73 i.— Volumetric Electricity 177 c— Physical and Chemical Ellectsol" Molecular > 111 • ■ \ 1 .'I • Electricity ) t?.— Acoustic Force, Motion ami Electricity... l'J5 e. — Dynaliiical qdects of Electro-Magnetisiii l!W (4) Suhjective auplicatiouH of Electric Force to iiiecliaii- j ical purposes 1 The Coal supply. The Past and Future 214 MMMHIi INDEX OF TLATES. 4« 51 VACiE. Tlate 1. — Tlio Form ami Rollcctioii of Wnvtw 94 11— Ititcrrcroncc nnd Infloxion of Wiwom })»» Plate — Fig. 7. — EclipHo compoiuulcd witii occultu- | tion of Jupiter's SutolliloH ' " Fijuj. 8. — Jupitor'H Slmdow und Kclipno of » Siitollito S Plate 9. — Tlio Plunot Jiipitov, the Eiirtli mid tlio Sun.. " 10. — Illu.stratioriH of Elcctricul Ajiiariitus (i9 " 11. — IlluHtrations of Magnetic Oui V08 175 " 12. — IlIuHtn-atioiiM of tlio linoH of AoouMtic Force.. 217 FioirRE 1. — IliuHtrating the Expansion rcquii'cd by theory in (the 8upi)oscd) aerial un- dulaliouH Figure 10. — The occnllation of Jupiter's second Satellite as seen from the nearest and from the most distant situations f of the Earth J FrorRE 11. — J^o. do. as soon from the first Satcl-^ lilo and from the Earth at con- Y junction j 104 46 54 "■': f- :f1 I ! ' m. m DARKNESS AND LIGHT. Hail, holy Light, offspring of Heaven first-born ! Or of tlie Eternal, co-eternal beam May I express thee unblanied ? since God is light, And never but in unapproachM light Dwelt from eternity, dwelt then in thee, , Bright effluence of bright essence increute. Ur were'st thou rather pure ethereal stream. Whose fountain who shall tell? before the sun. Before the heavens, thou wert, and at the voice Of God, as with a mantle, didst invest The rising world of waters dark and deep Won froui the void and formless infinite. Thee I revisit now with bolder wing. Escaped the Stygian pool, though long detainen In that obscure sojourn, while m my night Through utter and through middle darkness borne With other notes than to the Orphean lyre, 1 sung of Chaos and eternal Night, Taught by the heavenly Muse to venture down The dark descent, and up to reascend. Though hard and rare : thee I revisit safe, And leel thy sovereign vital lamp; but thou Kevisitest not these eyes, that roll in vain To find thy piercing ray, and find no dawn ; So thick a drop serenj hath quenched their orbs. Or dim suftusion veiled. Yet not the more Cease I to wander where the Muses haunt Clear spring, or shady grove, or sunny hill, Smit with tlie love of sacred son^ ; but chief Thee, Sion, and the flowing brooks beneath, That wash thy hallowed feet, and warbling flow, Nightly I visit: nor sometimes forget Those other two equalled with me in fate. So were I equalled with them in renown. Blind Thamyris and bUnd Mseonides, And Tiresias and Phineus, prophets old : Then feed on thoughts that voluntary move Harmonious numbers ; as the wakeful bird Sings darkling, and in shadiest covert hid Tunes her nocturnal note. Thus with the year Seasons return, but not tome returns Day i or the sweet approach of even or morn. Or sight of vernal bloom, or sunmier's rose. Or flocks, or herds, or human face divine ; But cloud, instead, and ever-during dark, Surrounds me 5 from the cheerful ways of men Cut of{, and tor the book of knowledge fair Presented with a universal blank Of nature's works, to me expunged and rased, And wisdom at one entrance quite shut out -, So much the rather thou, celestial Light, Shine inward, and the mind through all her powers Irradiate ; there plant eyes, all mist from thence Purge and disperse, that I may see and tell Of things invisible to mortal sight. John Miltoit, THE NATURE OF LIGHT. That which maketh manifest ia light. ^1.) The Corpuscular Emission Theory. * ' A theoretical explanation of the observed phenomena Taelonging to the subject of light, proposed by Sir Isaac Newton, is known as Newton's emission theory, or as it is sometimes called, the corpuscular theory of light. The following is the statement of the most important propositions contained in it : From Lardner's Natural Philosophy. '■' ' ''' ' ' 1222. " Corpuscular Theory. — In the corpuscular theory, which was adopted by Newton as the basis of his optical ; enquiries, light is considered as a material substance, con- , sisting of infinitely minute molecules which issue from luminous bodies and pass through space with prodigious velocities. Thus, in this hypothesis, the sun is regarded as a source from which such molecules or corpuscles pro- ceed in every direction, with such a velocity that they pass from that luminary to the earth, over a distance of ninety- five millions of miles in about eight minutes and thirteen seconds. This immense velocity with which they are endued, amounting to nearly two hundred thousand miles per se- cond, united with the fact established by observation, that they do not impress with the slightest momentum the B 10 THE CORPUSCULAR THEORY. " lightest objects which they strike, render it necessary to suppose that they are so minat« as to be altogether des- titute of inertia or gravity. The strongest beam of sunlight acting upon the most delicate substance, upon the fibres of silk or the web of the spider, or upon gold leaf, does not impress upon them the slightest perceptible motion. Now, in order that a particle of matter, endued with a velocity so great, should have no perceptible momentum, it is neces- sary to suppose it to be almost infinitely minute. But this minuteness requires to be admitted to a still greater extent; when it is considered that particle after particle, striking upon bodies so light, even after the dom- munication of their forces, impart to them no perceptible motion. 1223. " Difference of colour explained. — In this system the diiferenco of colour which prevails among the different homogeneous lights, the combination of which constitutes solar light, is ascribed to diflferent veloc' ties. Thus the sensation of red is producad by luminous mole- cules animated by one velocity, orange by anothei', blue by another, and so on." 122-i. " Laws of refraction and reflection explained. — The- law which renders the angle of reflection equal to the angle of incidence, is explained by supposing' such molecules to have perfect elasticity. The law of refivction is explained by supposing that such molecules are subject to an attrac- tion towards the perpendicular when they enter a denser, and by a repulsion from it when they enter a rarer medium." Objections to the Corxmscular Theory. Taking the statement of the theory just quoted. " In the corpuscular theory, which was adopted by Newton as the basis of his enquiries, light is considered as a material substance, consisting of infinitely minute molecules which issue from luminous bodies and pass I THE CORPUSCULAR THEORY. u through space with prodigious velocities." It neces- sarily follows, as a corollary, that when the sun has continued to shine for any length of time on a body which absorbs the light, a certain appreciable amount of the material projected from the sun, as light, will remain in that body, by which the gravity and mass of the body will be increased. Now if this actually happened it could not long remain unnoticed. Lardner himself remarks, in reference to the hypothetical particles which, according to the theory, issue from luminous bodies*, it is necessary to suppose that they are so minute as to be altogether destitute of inertia or gravity. " The strongest beam of sunlight acting upon the most delicate substance, upon the fibres of silk, or the web of the spider,, or upon gold-leaf, does not impress upon them the slight- est perceptible motion. Now, in order that a particle of matter endued with a velocity so great should have na perceptible momentum, it is necessary to suppose it to be almost infinitely minute." It is evident that Dr» Lardner, in writing this, must have been misled by the theory itself and the authority of Newton into stating a supposition which it is not scientifically permissible to entertain. By the expi'ession p..rticles almost infinitely minute ismeant particles extremely sraall,?. e., particles of very small size. But the gravity of a material substance, whatever its size may be, cannot be got rid of by divid- ing and sub-dividing it into very small or into extremely minute parts ; its gravity cannot in such a manner be even lessened. The sum of the gravities of the very- small, or of the extremely minute parts wiU exactly make up the gravity which the entire body- possessed, previously to its division. Take, for in- n THE CORPCSCULAK THEORY. stance, a pound by weiglit of any substance, and suppose it to be divided into a million parts, each of the parts being exactly similar and of the same size; then, each of those parts will weigh the one millionth of a pound, and, if one of them were to be again divided into a thousand parts, then one of those products of the sub-division would weigh the one thousandth of the millionth of a pound. The last particles would be very small, but nevertheless, if a thousand millions of them were projected by the sun in the course of an hour on to any one particular spot, a quantity of the material amounting to a pound in weight thereof would be the aggregate product at the end of that time. And again, how is matter, whether the particles be large or small, to move with an enormous velocity without having or acquiring momentum? Gravity, when motionless, [i. c, when restrained from moving] and momentum, when in motion, are two of the characteristic properties of matter, by which is meant some moterial thing whether it be an aggregated mass of enormous bulk, such as the planet Jupiter, or the most minute particle that can be imagined. Dr. Lardner also states that : " The law of refraction is explained by supposing that such molecules are subject to an attraction towards the perpendicular when they enter a denser, and by a repulsion from it when they enter a rarer medium." Now this is no explanation in a scientific sense; so far from it, such a supposition is inadmissible unless supported by some proof or evidence outside the theory. There is no support in this case, but on the contrary the suggestion is quite gratuitous and altogether improlrable. Why should a molecule of THE CORPUSCULAR THEORY. la ^1 ^m matter be attracted by a perpendicular to a denser, or be repelled by a perpendicular to a rarer, medium ? It has been long since established as a fact, by the results of numerous careful experiments and observation, that a ""v of light, on entering a denser from a rarer medium is refracted towards a perpendicular to the sur- face at which it enters, and, on entering a rarer from a denser medium, is refracted from a perpendicular to the surface of the rarer medium, at which it enters. When asked to give a reason, it is scientifically correct to say in reply that it is according to, oi in obedience to, the law of the refraction of hght, which is recognized as an estoblished law belonging to the science of Optics, be- cause demonstrated by the observed facts, of which, or from which, it may be said to be a generalization. But when we wish to proceed further, and to explain the particular nat'ire and properties of the ray of light which is so refracted, and to refer the law of the refraction of light to a more general or primary law, and thus to ex- plain particularly the cause of the ray being refracted according to the law, it will not then be in accordance with the rules of sound science to invent a cause ex- pressly for the purpose of the explanation ; namely, to suppose a unique cause unsupported by experimental evidence or by analogy ; such, for example, as a force elsewhere unknown or unrecognized, or a known force as acting in a manner unprecedented and elsew^here unobserved. To do this would be not to explain,, but to build up prejudice in the way of scientific explanation. If more sound and certain knowledge cannot be obtained on a particular subject, it is unadvisable to dilute with uncertain, and worse than useless to vitiate with false u THE UNDULATORY TIIEOHY. and unsound knowledge, that which we do ah-eady possess. (2.) Tlie Undidatory Theory. In consequence of the corpuscular emission theory being found insuificient lo satisfactorily explain some of thf) more recently observed phenomena of light, belong- ing iii particular to what is termed interference, it has been generally given up, and, in its place, the undula- tory theory of light has been adopted as the recognized basis of optical science. The undulatory theory is of almost the same age as the emission theoiy of Newton, having been first proposed and adopted by Hooke and Huygens, contemporaries of Newton ; it is only, how- ever, since the commencement of the present century that this theory has been more completely developed, and still more recently that it has been generally (now, almost unanimously) adopted. This theory is also sometimes called the wave-theory of light, and it has been primarily derived from what is known as the wave-theory of sound*, light being considered as the effect of an undula- tion or agitation propagated through and by means of the particles of a subtle and extremely elastic fluid called ether / analagous to the effect of the wave agitations of the particles of air, or other gaseous fluid, which accord- ing to the wave-theory is recognized as causing the effect, or class of effects, denominated sound. Lardnefs Natural Philosophy. ' ■" < 1225. " Undulatory Theory. — In the undulatory theory which was adopted by Huygens, and after hira by most continental philosophers, light is regarded as in all respects analagous to sound. ' ; ' * ~m THE UNDULATORY THEORY. 15 *' Tho luminous body in this system does not transmit anj' matter through space :y more than a bell transmits matter %vhon it sounds. The luminous body is regarded as a centre of vibration; but in order to explain the transmission of this vibration through space, the existence of a subtle fluid is assumed, which plays, with regard to light, nearly the same part as the atmosphere plays with regard to sound. The sun, in this theory, then, is a centre of vibra- tion, and the space which surrounds him being filled with an atmosphere of this subtle fluid, transmits this vibration «xactly as the atmosphere transmits the vibration of a sounding body." 1226. " The Luminous Ether. — This hypothetical fluid has received the name of ether. It is supposed not only to fill all the vacant spaces of the universe which are unoccupied by bodies, but also to fill the interstices which exist between the component parts of bodies. Thus it is not only mingled with the atmosphere which surrounds the earth, but also with *he component parts of water, gla^s, and all trans- parent substances ; and since opaque substances, when rendered iiufficiently thin, are penetrable more or less by 'light, it is necessary to admit that it also fills the pores of such bodies. If this luminous ether did not prevail through- out the whole extent of the atmosphere, the light of the stars could not reach our eyes. If it did not exist in water, glass, precious stones, and all transparent substances, these 'Substances could not be penetrable by light as they are ; in -fine, if it did not exist in the humours of the eye, light could ^not affect this organ, and the undulations could not reach the membrane of the retina." !, 1227. ^^ Effects ascribed to its varying density. — But although this luminous ether is thus assumed to be omni- present, it does not everywhere prevail with the same density. It is probable that its density in the celestial spaces which intervene between planet and planet is the SI THE UNDUIiATOBY TIIEORT. " Hamo which it has umier tho exhausted receiver of an air^ pump or alx)vo the morcu""^! column in a barometer. But its density in transparent media must bo different, because to explain tho plienomena of light passing through them it is necessary to suppose that the undulations change their magnitude, a supposition which is only compatible with a change in the elasticity of the ether. We shall soo further, that in some transparent bodies existing in a crystal- lized slato it is necessary to suppose also that the density of tho other in different directions in the same medium varies. If this universal ether were for a moment in a stale of perfect repose, tho universe would be in absolute darkness ; hn\ tho moment its equilibrium is disturbed, and that an undulation or vibration is imparted to it, that instant light is created, and is propagated indefinitely on all sides, as, in an atmosphere perfectly tranquil, the vibration of a musical string or the sound of a blow is propagated to a distance in all directions according to determinate laws. • > : '. Light itself, must not, however, be confounded with tho other which is the medium of its propagation. Light is no more identical with the hypothetical ether than sound is identical with air. The ether, in the one case, and the air in tho other, are merely the nedia by which the systems of undulations which constitute tho real sense of light and sound are propagated." • - t • ■ I'sj? : ,;•• .i <■ .• 1228. " Analogy of light and sound. — In considering tho analogy between light and sound, however, there is an important distinction which must not escape notice. Sound is propagated, not only by undulations transmitted through the air, but also by undulations transmitted through other fluids as well as solids, as has been already explained. Light, nowever, according to the undulatory theory, is transmitted only by the undulations of the luminous ether. Light, therefore, does not pass through a transparent body, such as glass, in the same manner as sound is transmitted THE ■TBER. 17 through tho same body. The undulations by which sound is propagated through tho air would bo imparted to glass itsolt, which will continue them and transmit them to another portion of air, and thence to the ear ; but when tho undulations of li^ht are transmitted tiirough glass or any other transparent medium, they must be supposed to bo propagated, not by tho vibration of the glass itself, but by tho vibration of the subtle ether which pervades its pores." Objections to the Undulatory Theory. The Ether. — The supposed fluid thus named is usually spoken of by writers on optics as a hypothetical fluid ; but such a use of the expression ' hypothetical' is apt to .nislead. . . if the writer, who so uses the word, supposes at the same time that the u adulatory theory of light is scientifically established. If the expression 'hypothetical' is merely intended to indicate that the supposed subtle fluid, the ether, cannot be directly taken cognizance of by the senses, its use is objectionable jbecause many natural as well as all ideal facts are in the same case, .that is, they cannot be directly cognized by the senses. A belief that the undulatory theory of light is scientifically estab- lished, should include the belief that the existence of the ether is demonstrated by the observed facts and the legi- timate reasoning belonging to that theory. If the non- existence of the ether fluid were to be demonstrated, the undulatory theory of light, which is based upon its assumed existence, would necessarily have to be given up ; and therefore if, or so long as, the existence of the ether is in any degree doubtful, so long must the theory itself be in doubt, and must not be considered as scientifically estab- lished — ^merely a theory, not a demonstrated theorem. The expression ' subsensible' as applied by Prof. Tyndall to the (supposed) ether fluid is much preferable to * hypothetical,^ 18 THE ETHER. if the theory w acce^yted as demonstrated. In Dr. Liird- ner's statement of the undulatory theory, quoted at page 3, a concise explanation of the supposed nature of the lumi- nous ether will be found. Also in Prof. Tyndall's lecture on light, (Sec Appendix,) wherein the sound and light-waves are compared, tlie material and gaseous nature of the subsensible fluid is very distinctly assumed : " Could you see the air through which sound-waves are passing, you would observe every individual particle of air oscillating to and fro." " Could you see the ether, you would also find every individual particle making a small excursion to and fro." The general object of this part of the lecture is to show the analogy between light and sound I but we can scarcely be incorrect in supposing that the more particular object is to demonstrate the existence of the subsensible ether-fluid by thus showing and illustrating the analogy. A difficulty of a kind to make extreme caution neces- sary as to accepting the existence of the ether, until strictly demonstrated, is that the theory and the observed facts belonging to it together necessitate the assumption that the material subsensible fluid occupies all space, and that all other descriptions of matter, not absolutely opaque, must be considered porous, and as having their interior spaces all filled with ether. It appears that this undulatory theory of light became the subject of a conversation between Prof. Tyndall and Sir David Brewster, and that the latter stated his opinion as to the existence of the ether-fluid in the following words : " That his chief objection to the undulatory theory of light was that he could not think the Creator guilty of so clumsy a contrivance as the fiUing of (? all) space with ether in THE ITIIIR. 19 order to produce light." Oo which observation Prof. Tyn- dall, in his published lecture, page 40, makes this remark : " This, I may say, is very dangerous ground ; and the quarrel of science with Sir David, on this point, as with many other persons on other points, is, that they profess to know too much about the mind of the Creator." These observations bring a subject directly under consi- deration distinct from and of greater importance than the undulatory or other physical theory of light, and as it is also the subject to which, as stated in our introductory remarks, the more general purpose of our work is directed, Ave shall include in our notice of them an examination of their significance in reference to that more important sub- ject. The subject thus brought pa rticularly under considera- tion is the relation of science, or what is now considered as science, to the facts of creation and to the Creator Him- self, and therefore to theology. It may be said that the observations were not particularly intended to be applied in this sense, but they are made public, and they define in ii measure the position occupied at the present time by science, in this relation, according to the judgment of the speakers. The observation of Sir David Brewster was certainly blameworthy as being expressed in irreverent language. An observation made in such terms under any circum- stances cannot be reasonably regarded otherwise than as foolish and wrong ; but if made deliberately and guard- edly on a grave and important subject of science. . . and published ... an observation so expressed must be con- sidered blameworthy in a much higher degree. It should be remarked, however, on behalf of Sir David, that, in i I 20 SCIENCE AND THEOLOGY. this case, his obsei-vatian was probably in its form a care- less off-hand expression of opinion not intended for the public. Apart from the very reprehensible form of the expression, the meaning of the objection, which Sir David may be understood as intending to convey, does not appear to us by any means unreasonable. The supposi- tion of all space being filled with a material fluid for the purpose of producing effects at certain distant points, or. in other words an omnipresent material fluid filling and pervading the universe for the production of one class or kind of effect only, does not seem to harmonize with what we do know of the Creator's work but, on the contrary, it presents itself to the educated mind as a contrast to the directness and simplicity of the methods employed in other parts of creation. Notwithstanding the supposed attenuated subsensible characteristics of the fluid, the in- conceivably enormous quantity of material required by the theory at once suggests improbability. If, however, the objection went no further than this, it might perhaps be answered with some degree of force by supposing that the ether fulfilled other important purpose or pur- poses with which we are as yet altogether unacquainted, but the objection does go much further, because the ether fluid is, by the assumption, material, and upon this assumption the theory rests. Why, then, does not the ether, in obedience to the general law known to govern; and recognized as universally governing, matter, collect around the centres of giuvHating influence ? Are we asked to suppose the ethei to di-^er from all other varieties of matter, to be exempt from the influence of gravitation and at the same time to have other properties in common with the other descriptions, and to be controlled by some 111 SCIENCE AND THEOLOGY. , 2t of the laws governing other kinds, of matter; as, for ex- ample, to possess the property of elasticity, and to be capable of propagating an impulse by undulations of its particles ? To admit such a jjroposition even as an assump- tion is extremely dangerous. It is to take leave of all cer- tainty ; to bid farewell to science, and to set sail without rudder or compass on the dark and treacherous ocean of metaphysics. Very much of the sound natural science now possessed by us is based on the certain knowledge that gravitation is a general law governing all matter. If this is uncertain, or is to be considered uncertain and open to controversy, where, then, are we to find scientific certainty in respect to the material world ? If any one variety of matter may be exempt from such a general law, so also may other varieties. If the reply to this should be . . well, then, the ether in that sense is not material; it is evident that the undulatory theory of light must At once fall to the ground, because it rests upon the assumption that the ether is a material fluid, possessing ^some of) the properties belonging essentially and distinc- tively '"O all matter. >. ;■ , . Prof. Tyndall does not, however, make any direct reply to the objection of Sir David Brewster, but there- upon makes a statement in the name of science, against which statement we feel obliged, also in the name of science, to protest. The statement or remark is perhaps not quite so definite as to preclude the possibility of mis- apprehension as to its full meaning ; but we are afraid that the meaning which it will be generally understood to convey is that the mind of the Creator, as displayed in, and made known to us by and through, the facts ol creation, is not the proper and legitimate subject for 22 SCIENCE AND THEOLOGY. science to occupy itself about. Moreover, a meaning- may be understood to be indirectly included to the effect that the ' reason ' or ' reasonableness ' of the Creator is different in kind from the ' reason ' or ' reasonableness ' of human science. Now, rissuming that either or both of these meanings are to be understood, we have to state directly to the contrary, that the express object and purpose of science, in any high sense, is to obtain know- ledge, a better and more perfect knowledge, and always more knowledge of the mind of the Creator ; and that having obtained such knowledge, the legitimate and best employment of those who have acquired such knowledge is in teaching and making known the mind of the Creator for the guidance of those who have not the oppor- tunity to seek this higher kind of knowledge for them- selves. In reference to the (inferential) secondary meaning mentioned above, we would say that, if we had not an assured belief as to human reason (terrestrial reason"). being in harmony w'th, based upon, and the same in kind as the Reason of the Creator (celestial reason)^ science, in any higher sense, would lose its interest for us. A merely human science — which h not a part of universal science, and which, so far as any one man is concerned, is confined to the few years of a man's terres- trial existence — does not appear to us a very desirable or interesting pursuit, merely for its own sake. A man crammed full of scientific knowledge is not, therefore, necessarily, in a merely terrestrial sense, happier than a man who possesses very little, nor is he likely to be physically stronger or better developed in consequence. Prof. Tyndall highly values scientific knowledge, so da SCIENCE AND THEOLOGY. 23 'm we f he also expresses a sort of compassion for those who- do not know, and a certain degree of contempt for those who contemn, science in the higher sense — and which feeling we also share ; but it is because we believe that in acquiring scientific knowledge we are acquiring, and in communicating scientific knowledge we are commu- nicating, that which belongs, not merely to a brief ter- restrial, but, also, to a higher state of existence, and which may be considered as belonging to, and forming a part of, immortality. If we did not so believe, we should incline to the opinion that the practical-sense men who say ' cui bono ' when invited to engage in scientific pursuits, and who can see no use in science except as a means, or as furnishing the means of ameli- orating the hardships of human existence and of increas- ing the amount of sensual ease and enjoyment — the practical sense and common-sense men, who so argue,, would in that case, as we opine, have much the strongest argument ; for other purpose or in other sense — for its own sake, for instance, meaning thereby the gratification supposed to arise from feeling more highly cultured or more intellectually developed than others, the man ardently devoted to the acquisition of scientific knowledge may be justly considered as on a par with, or, at least, not much better than, the man devoted to the acquisition and accumulation of material wealth. For where, in such a sense, is the diflference ? In either case it is the selfish endeavour to acquire the possession of wealth for its own sake . . i.e., for the grati- fication of a desire to be richer than his fellows. If the reply to this should be . . . That is not what we mean or understand by studying science for its own sake. 24 SCIENCE AND TIIEOLOQY. m The man who in the higher sense devotes himself to the acquisition and promotion of scientific knowledge does so unselfishly ; he knows that he can live for a few years only and enjoy for a short time only a very partial pos- session of the knowledge he thus acquires, but he believes that he is assisting to build up that which will endure permanently and, by elevating their condition and in- creasing their intellectual happiness, will benefit his successors for untold ages. Yes . . but if this is the mean- ing, it must in reason be based upon the belief that human science is in harmony with, belongs to, and is a part of celestial science, and that, therefore, the express object of human science is, by persistent endeavour and efibrt, to make sure that it belongs to the Mind of the Creator and to learn more of that Mind : for, otherwise, there can be no assurance of permanence, nor can there be any assurance, even, that the value of such science is anything more than suppositious, since it may be in a ce- lestial sense, false. Moreover, is the man sure that he will live and possess the knowledge which he has acquired, for a few years only ? . . . does he usually Work in that belief ? Where is the man of science who cares nothing about the posthumous credit of an important discovery which he has made, or is quite careless as to whether his re- putation will endure and his name be held in honour and respect by succeeding generations ? The objection which we have just stated, in the fore- going amplification of Sir David Brewster's objection, viz., to the assumption of ether as a form of matter exempt from the influence of gravitation, appears to us to be, of itself, altogether fatal to the undulatory theory of light, and to render the acceptance of that theory scientifically TWO OMNIPRESENT ETHERS. 26 inadmissible ; but even if the suppos'tion were to be en- tertained that this objection might be, in some way or other, surmounted, and the actual existence of the ether shown to be theoretically possible, there would yet re- main, at least one serious difficulty which has been, as it seems to us, put aside, rather than dealt with and sur- mounted by the supporters of the theory. We allude to the kindred phenomena of radiant heat. The nature of this particular difficulty may be thus briefly stated :— the phenomena of light and of radiant heat are so analo- gous, so evidently allied and similar to each other, in many respects, that it is almost, if not quite, impossible in a, reasonable sense to suppose the one effect (or class of effects) to result from the undulation of an elastic material fluid and not to suppose the other effect (or class of effects) to be produced in the like manner ; but although there are very close analogies between the two kinds of effect (or classes of phenomena) in some res- pects, there are also differences of an essential and dis- tinctive character, such that we should feel at least a very grave difficulty as to admitting even a theoretical supposition that a mere variation in the velocities of the undulations of the same fluid can occasion them. We say that the difference in the characteristics of light and radiant heat are too great, and of essentially too distinc- tive a kind, to allow the supposition that a certain num- ber of undulations, or vibratory pulses of ether, taking place in a second of time may produce light, and that a certain lesser (or greater) number of vibratory pulses, in a second, may be productive of radiant heat. What is the alternative ? To suppose the existence of two diffe- rent omnipresent et) .rs ? 'Jld SCIENCE AND METAPHYSICS. Before leavirg for the present the important que^tionc as to the position which science, in its higher signification, does or ought to occupy, we will make some remarks as to the meaning which correctly belongs to the tejm metaphysics, in its relation to science. The indefinite- ness which constitutes one of the leading characteristics of metaphysics, attaches in some degree even to tht name or expression by which it is denoted, in such wise that probably no two scientifically educated persons could be found at the present time to agree as to what ought or ' ought not to be included in a strict sense under that title. To make our remarks as brief and subjective as the nature of the subject will permit, we will give here one example of the confusion of thought, and inferential mystification instead of increased knowledge, which re- sults from that indefiniteness. In the work of Sir John Herschel, Outlines of Astronomy y from which we have made many quotations, we find a note, at the foot of page 212 as follows : " This condi- tion is indispensable. Without it we fall into all those difficulties which M. Doppler has so well pointed out in his paper on aberration. (Abhandlungen der k. boe- mischen Gesellschaft der Wissenschaften. Folge V. vol. iii.) If light itself, or the luminiferous ether, be corpo- real, the condition insisted on amounts to a formal sur- render of the dogma, either of the extension or of the impenetrability of matter ; at least in the sense in which those terms have been hitherto used by metaphysicians. At the point to which science is arrived, probably few will be found to maintain either the ^>ne or the other. "^^ The indispensable condition referred to is stated in the- SCIENCE AND METAPHYSICS. # text above. '" In whatever manner we consider lights whether as an advancing wave in a motionless ether, or a shower of atoms traversing space, (provided that in both cases we regard it as absolutely incapable of suffer- ing resistance or corporeal obstruction from the particles of transparent media traversed by it.)*' The words within the brackets expressing the condition insisted upon. ■ . ♦ The doctrine of the impenetrability of matter is thus stated by Lardner, in his Natural Fhilosophy* (22) " All matter impenetrable. — Impenetrability is the quality in virtue of which a body occupies a certain space, to the exclusion of all other bodies. This idea is so insepa- rable from matter, that some writers affirm that it is nothing but matter itself; that is, that when we say that a boUy is impenetrable, we merely say that it is a body. However this be, the existence of this quality of impene- trability is so evident as to admit of no other proof than an appeal to the senses and the understanding. No one can conceive two globes of lead, each a foot in diameter, to occupy precisely the saape place at the same time. SucR a statement would imply an absurdity, manifest to every understanding." 23; " Gaseous bodies impenetrable.— Even bodies in the gaseous form, the most attenuated state in which matter can exist, possess this quality of impenetrability as positively as- the most hard and dense substances." Now this doctrine, or teaching, as to one of the recog- nized properties of matter, is, if we understand Herschel's •Extension is not distinguished by Lardner as one of the properties of matter ; probably he considered it synonymous with magnitude, oi' perhaps, as merely expressing the existence and natural reality of matter. 28 SCIENCE AND METAPHT8ICS. remarks aright, considered by him to be a metaphysical dogma, and no longer tenable in a strictly scientific sense ; and, moreover, he supposes, it would seem, there are now but few persons of scientific education who think differently. Two distinct questions are herein involved, both of them of much importance. The one is, whether that science, which has and professes a definite belief in the existence of matter, such as defined by Lardner, is sound science or the reverse. The other question is, the cor- rect use of the expression *■ metaphysics.' It is witn respect to the last of these questions that we think it desirable to make here a few observations. The particu- lar word 'metaphysics ' may, of course, be used, as any word in nomenclature may be used, in whatever sense it may be generally agreed to use and understand it. But the important question here at issue is, (1st) — Whether iill knowledge, all that is supposed to be, or goes by the name of, knowledge, of every kind and description, if only it be classified and systemized, is to be called and considered * science ; ' or, (2nd) — Whether it is necessary there should be a distinction and separation of the cer- tain and sound knowledge, from the uncertain and un- .sound. . .»-;..,..:,.....; Now the necessity of a division has been for a long time past generally recognized ; for instance, that de- scription of classified knowledge which at an earlier pe- riod was admitted and highly reputed under the title *■ astrology ' and which, since the time oi Francis Bacon, has ceased to be considered a part of the classi- fied knowledge belonging to science. If, therefore, it is right and proper to have a division and to have an expres- i v\ SCIENCE AND METAPHYSICS. 29 sion ' science,' to denote collectively all the descriptions of knowledge considered beneficial and to be worth pre- serving and cultivating, it is likewise desirable to have a general expression to denote collectively those descrip- tions of knowledge, systematically classified or otherwise^ which are o^ the opposite character from the former — that is, which are, or ought to be, under a strictly cor- rect division, excluded from science. It is in this sense that we understand and purpose to use the expression ' metaphysics,' because certain classified descriptions of knowledge which ought, according to our judgment, to be excluded from science, are already particularly denoted by that expression, and, moreover, the indefinite and mystical meaning which the expression suggests to the generality of people, makes it the more suitable as a collective expression for all kinds of knowledge which are indefinite, uncertain and unsound. The mode of its use by Sir John Ilerschel, in the pre- ceding quotation is, therefore, according to our view, an inversion of the correct or desirable application of the term, ' metaphysics ;' for, therein it is used to denote the definite teaching — i e., the recognition and intelligible definition of the natural reality ; and, by inference, the expression ' science ' may be understood to apply to the indefinite teaching — viz, to that which is indefinite and unintelligible. We find in Prof. Tyndall's Lectures on Light,* page 55, the indirect statement of, what appears to ua to constitute, another difficulty in the way of accepting the undulatory theory. That statement reads : " All space * See quotation in the Appendix. h'rrr-i-ir 30 THE UNDULATORY TIIEORT. I \h filled with matter oscillating at such rates. From every star waves of these dimensions move with tlie velocity of light, like spherical shells, outwards. And in tlie ether, just as in the water, the motion of every particle is the algebraic sum of all the separate motions imparted to it. Still, one motion does not blot the other out ; or, if extinction occur at one point, it is atoned for at some other point. Every star declares by its light its undamaged individuality, as if it alone sends its thrills tlirough space." It is an observed fact and unquestionably true that every star does so declare its undamaged individuality ; but how can these undulations, which are defined by the tlieory to be of the nature of waves or of piogressive oscillations resulting from motion in the particles of a material fluid ... we ask, how can these undulations reach us in innumerable quantity at the same time and from every direction, and yet not damage, modify, inter- rupt, or, in any way, interfere with each other ? It is not only from every star and every luminous liody that these undulations have to reach the eye in undamaged individuality, but, if we apprehend the explanations of the theory aright, also from eveiy visible object. At the rate of only one undulation in a second it would be embarrassing even to imagine these undulations crossing each other in every direction without mutual inter- ruption, but what is the estimate of the number by those who support the theory ? " All these waves enter the eye, and hit the retina at the back of the eye, in one second. The number of shocks per second necessary to the production of the impression of red is, therefore, four hundred and fifly one millions of millions. In a similar VBt-OCITY-OP-LIOHT THEORV. 31 manner, it may be found that the number of shocks cor- responding to the impression of violet is seven hundred nnd eiglity-nine millions of millions. All space is filled with matter oscillating at such rates." • We do not find any explanation of this difficulty even attempted ; an occasional or possible interference is alluded to by the remark that " if extinction occurs at one point, it is atoned for at some other point ;" but, with the various effects, classed as the phenomena of inteifer- pnce and belonging to Optics and Acoustics respectively, in mind, we feel only that this last remark increases our inability to accept the proposition by making the impos- sibility of reconciling the theory with the known facts of science still more apparent. (3.) Velocity of Light theory. Both of these theories, the corpuscular, and undula- tory theories of light, which have been successively accepted and adopted as forming a part of optical science, liave one primary basis in common, namely, the velocity of light, which is assumed to have been antecedently established as an observed fact. Since we have objected, for reasons more or less fully stated, to the acceptance of either of these theories as be- longing to sound science in the sense of demonstrated theorems, we propose now to examine the evidence as to that alleged velocity of light which is assumed to have been antecedently established. The history of this (assumed) discovery or observation, we find from the general record to be briefly as foUo ws : * Lectures on Light, page 65. (See quotation in the Appendix.) 32 VELOCITY-OF-LIOHT TIIXOBY. Lardner^a Astronomy. (2969). ** Motion of light discovered and its velocity nitflswrej.— Soon nftertho invention of the telescope, Eoomer, an eminent DaniHh aHtronomor, engaged in a series of ol»- scrvntions, the object of which was the discovery of the exact time of the revolution of one of those bodies around Jupiter. The mode in which he proposed to investigate this was by observing the successive eclipses of the satel- lite, and noticing the time between them. Now if it were possible to observe accurately the moment at which the satellite would, after each revolution, either enter the shadow or emerge from it, the interval of time between thcKo events would enable us to calculate exactly the velocity and motion of the satellite. It was, then, iu this manner that Roemor proposed to' ascertain the motion of the satellite. But, in order to obtain this estimate witii the greatest possible precision, he proposed to continue hi» observations for several months. .- ;, .:, Lot us, then, suppose that we have observed the time which has elapsed between two successive eclipses, and that this time is, for example, forty-three hours. We ought to expect that the eclipse would recur after the lapse of every successive period of forty-three hours. Imagine, then, a table to be computed in which wo shall' calculate and register before hand the moment at which every successive eclipse of the satellite for twelve months to come shall occur, and let us conceive that the earth is at A, at the commencement of our observations ; we shall then, as Roomer did, observe the moment at which the eclipses occur, and compare them with the moments registered iu the table, tt ijn-i'^-i -.ju r ^ Let the earth, at the commencement of those observa- tions, be supposed at E. fig. 756, where it is nearest to VBLOCITT-OF-LIOHT THCORT. 3» "Jupiter. When the earth hns moved ioE," it will bo founr to him ors of his night be i of irre- ih errors, ae would than the jarlier to observed, observed ime, and iter con- m effect, to arise have its id. The juestion, ntinuing lied on, ;, moved :he time 8 not so Toached ntil, on bserved utation. nt that on the VELOCITV-OF-LIGHT THEORY. m Increased distance of the earth from Jupiter. The great- er that distance, the later was the occurrence of the eclipse as apparent to the observers, and on calculating the change of distance, it was found that the delay of the eclipse was exactly proportional to the increase of the earth's distance from the place where the eclipse occurred. Thus, when the earth was at E.'" the eclipse was observ- ed sixteen minutes, or about 1000 seconds, later than when the earth was at E. The diameter of the orbit of the earth E. EJ" measuring about two hundred millions of miles, it appeared that that distance produced a delay of a thousand seconds, which was at the rate of two hun- dred thousand miles per second. It appeared, then, that for every two hundred thousand miles that the earth's ■distance from Jupiter was increased, the observation of the eclipse was delayed one second. . Such were the facts which presented themselves to Roomer. How were they to be explained ? It would be absurd to suppose that the actual occurrence of the eclipse was delayed hy the increased distance of the earth "from Jupiter. These phenomena depend only on the motion of the satellite and the position of Jupiter's shadov, and have nothing to do with, and can have no dependence on, the position or motion of the earth, yet unquestionably the time they appear to occur to an observer upon the earth, has a dependence on the distance of the earth from Jflpiter. ■ ir . . To solve this difficulty, the happy idea occurred to Koeraer that the moment at which we see the extinction of the Batellite by its entrance into the shadow is not, in any case, the very moment at which Lhat event takes place, but sometime afterward, viz., such an interval as is sufficient for the light, which left the satellite just before its extinction, to reach the eye. Viewing the matter thug, 86 VELOCITT-OF-LIGHT THEORY. I: i' I ' I ::rl- " it will be appm-ent that the more distant tlie earth is from the satellite, the longer will be the interval between the extinction of the satellite and the arrival of the last por- tion of light, which left it, at the earth ; but the moment of the extinction of the satellite is that of the commence- ment of the eclipse, and the moment of the arrival of the light at the earth is the moment the commencement of the eclipse is observed. Thus Roemer, with the greatest felicity and success, explained the discrepancy between the calculated and the observed times of the eclipses; but he saw that these circumstances placed a great discovery at his hand. In short, it was apparent that light is propagated through . space with a certain definite speed, and that the circum- stances we have just explained supply the means of mea- suring that velocity. We have shown that the eclipse of the satellite is delayed one second more for every two hundred thousand miles that the earth's distance from Jupiter i-i' increased, the reason of which obviously is, that ligi'l lakes one second to move over that space; hence it is .-p, . rent that the velocity of light is at the rate, in round nuoauers, of two hundred thousand miles per second. By more exact observation and calculation the velocity is found to be 192,000 miles per second, the time takea in crossing the earth's orbit being 16m. 26. Cs." Having herein the history and particular definition of the observed facts upon which the theory of the velocity of light is supposed to be directly based, we will now quote, also from the same work {Lardpcr's Astronomy)^ the more general explanation of the phenomena belong- ing to these facts, in order that the whole of the case may be clearly understood. il VELOCITY-OF-LIGHT THEORY. 3t Eclipses, Transits, and Occultations of the Jovian System. (2950) " The motions of Jupiter and his satellites, ns seen from the earth, exhibit, from time to time, all the effects of interposition. Let J. J.' fig. 810, represent the planet, J. f. J' itr> conical shadow, S. S, the sun, E. and E.' the positions of the eurth when the planet is in quadrature, in which position the shadow «/. /. J.' is presented with least obliquit}- to the visual line, and there- fore least foreshortened, and niost^ distinctly seen. Let b. 6/ d.' d. represent the orlnt of one of the satellites, the plane of which coincides nearly with that of the planet's gg ^ VELOCITY-OF-LianT TBEORY. " orbit, and, for the purposes of the present illustration, the- latter tony be considered as coinciding with the ecliptic ■without producing sensible error. From E. suppose the visual lines E. J. and E.J.' to be drawn, meeting the path of the satellite at d. and g., and a.' and b.', and in like manner, let the corresponding visual lines from E.' meet it at d.' and g.', and at a. and 6. Let c. and c/ be the points where the path of the satellite crosses the limits of tho shadow, and h. and h.', the points where it crosses the extreme solar raj - which pass along those limits. If I express the lerigth Jf of the shadow, d the distance of the planet from the sun in semi-diameters of the planet, and r and r' the semi-diameters of the sun and the planet respectively, r' we shall have (2917) I = d x r-r' B\iid=1122n r=441000 r'=44000 44 and therefore ?= 11227 x =1247: 441-44 that is to say, the length of the shadow is 1247 semi-diame- ters of the planet. Nqw, since the distance of the most remote satellite is not so much as 27 semi-diameters of the planet (2760), and since the orbits of the featellites are almost exactly in the plane of the orbit of the planet, it is evident that this will necessarily pass through the shudoiv, and almost through its axis, every revolution, and tho lengths of their paths in the shadow will be very little less than the diameter of the planet. ' - - t .',• The fourth satellite, in extremely rare cases, presents an exception to this, passing through opposition without enter- ing the shadow. In general, however, it may be considered that all the satellites in opposition pass through." ' {Note. This last statement about the fourth satellite ap- ])ears very remarkable in connection tcith that which pre- VELOCITY-OF-LIOHT THEORY. cedes it, and ivitli the great breadth of the shadoiv. But if we assume a moderate amount of vertical deviation above and behtv the orbital plane oftheplanefs equator, it becomes quite intelligible why the fourth satellite sometimes passes through opposition without entering the shadoiv.) (2951) *^ Effects J interposition. — The planet and satellites exhibit, from time to time, four ditferent effects of inter- position." ^ (2952) " Ist. Eclipses of the satellites. — These take place when the satellites pass behind the planet. Their entrance into the shadow, called the immersion, i marked by their sudden extinction. Their passage out of the shadow, called their emersion, is manifested by their being suddenly relighted." (2953). 2nd. " Eclipses of the planet by the satellites. — . When the satellites, at the periods of their conjunctions, pass between the lines S J, and S' J', their shadows are projected on the surface of the planet in the same manner as the shadow of the moon is projected on the earth in a solar eclipse, and, in this case, the shadow may be seen moving across the disk of the planet, in a direction parallel to its belts, as a small round and intensely black spot." (2954), 3rd. " Occultations of the satellites by the planet. — When a satellite, passing behind the planet, is between the tangents E.J.a'., and E.J.b'., drawn from the oarth, it is con- cealed from the observer on the earth by the interposition of the body of the planet. It suddenly disappears on one side of the planet's disk, and as suddenly reajjpears on the other side, having jiassed over that part of its orbit which, is included between the tangents. This phenomena is called an occultation of the satellite." (2955). " Transit of the satellites over the planet. — When a satellite, being between the earth and planet, passer between the tangents E.J. and E'.J., drawn from the earth to the 40 VELOCITV-OF-LIOHT THEORY. I!l ''* "planot, its disk is projected on that of the nlanet, and it.may Tic seen passing across, us a small brown spot, brighter or darlter than the ground on which it is projected, according as it is projected on a dark or bright belt. The entrance of Iho Fatelllto upon the disk, and its departure from it, are denominated its ingress and egress." (2956). ^' All these phenomena wanifested at quadrature. — When the planet is inPquadrature. and the shadow therefore presented to the visual ray with least effect of foreshortening, nil these several phenomena may be witnessed in the revo- lution of each satellite. The earth being at E. or E'., the visual line E.J. or E.'J.' crosses the boundary x.' or x. of the shadow at a distance x'. J. ' or X. J., from the planet, which bears the same ratio to its diameter as the distance of Jupiter from the sun bears to the distance of the earth from the sun, as is evident from the figure. But Jupiter's distance from the sun being five times that of the earth, it follows that the distance x.J. is five diameters, or ten semi-diameters, of the planet. But since the distance of the first satellite is only six, and that of the second somewhat less than ten, semi-diameters of the planet, it follows that the paths of these 'tw^o will lie within the dis- tance X.J. or x.'J.' The planet being in quadrature 90** behind the sun, the •earth w'll be at E. and the entire section c. c' of the shadow, at the distances of the third and fourth satellites (which are 15 and 27 semi-diameters of the planet respectively), ■will be visible to the west of the planet, so that when these satellites, moving from b, as indicate 1 by the arrow, pass through the shadows, their immfsion and emersion will be both manifested on the west of the planet, by their sudden disappearance and reappearance on entering and emerging from the shadow at c. and c' But the section of the shadow, at the distances at the first and second VELOCITV-OF-LIOHT THEORY. 41 " satellites, being nearer to the planet than x.x.' will be visible only at its western edge, the planet intercepting the visual ray directed to the eastern edge. The immersion, therefore, of these will be manifested by their sudden disappearance on the west of the planet, at the moment of their immersion ; but the viewof their emersion will be intercepted by the body of the planet, and they will only reappear after having passed behind the planet. The third and fourth satellites, after emerging from the shadow at c'. and appearing to be re-lighted, will again be extinguished when they come to the visual ray E. J. a', which touches the planet. The moment of passing this ray is that of the commencement of their ocoultation by the planet. They will continue invisible until they arrive at the other tangen- tial visual ray E. J.'b.', when they will suddenly reappear to the east of the planet, the occupation ceasing." " In the cases of the first and second satellites, the com- mencement of the occultation preceding the termination -of the eclipse, it is not perceived, the satellite at the moment of the interpositon of the edge of the planet not having yet emerged from the shadow. In these cases, therefore, the disappearance of the satellite at the com- mencement of the eclipse, and its reappearance at the termination of the occultation, alone are perceived, the emersion from the shadow being concealed by the occulta- tion, which has already commenced, and the disappear- ance at the commencement of the occultation being pre- vented by the eclipse not yet terminated. ■ ; • When the satellite, proceeding in its orbit, arrives at Ji.' its shadow falls upon the planet, and is seen from the earth, at E, to move across its disc as a small black spot, while the planet moves from L' to h. ^ When the planet arrives at g. it passes the visual ray E, J.' and while it moves from g, to d. its disc is projected 42 VELOCITT-OP-LIOHT THEORY. " on that of the planet, and a transit takes place, a»- already described. ,;*; Thus, at quadrature, the third and fourth satellites pre- sent successively all the phenomena of interposition : 1st, an eclipse of the satellite to the ■■■^est of the planet shows both immersion and emersion ; 2nd, an occultation of the satellite by the planet, the disappearence and reappear- ance being both manifested ; 3rd, the eclipse of the planet by the satellite ; and 4th, the transit of the satellite over the planet." ■..•!■ • . ■ • : ; ;i: :»- ;; , > li '^ * (2957) " Effects modified at other elongations. — There is a certain limit, such as e, at which the emersion of the third and fourth satellites is intercepted, like that of the- first, by the body of the planet. This is determined by the place of the earth from which the visual ray e. J. c' is directed to the eastern edge of the section of the shadow at the planet's distance. Within this limit the phenomena for the third and fourth satellites are altogether similar, to those already explained in the cate of the first and second satellites seen from E. ■'•.■■ "" " When the earth is between 5., and s'. no eclipses can be witnessed. Those of the satellites are rendered invisible by the interposition of the planet, and those of the planet by the interposition of the satellites. When the earth is at e'.' and E.', the phenomena are similar to those mani- fested at €. and E., but they are exhibited in a dif- ferent order and direction. The occultation of the satel- lite precedes its eclipse, and the latter takes place to the east of the planet. In like manner, the transit of the satellite precedes the eclipse of the planet." , ,,«.,, ^ ,, Examination oftlie Becord. ' ' "' '.""'. '■'' In carefully examining the recorcl of the phenomena together with the explanation contained in the foregoing^ we particulary note the very positive assumption that VELOOITY-OF-LIOHT THMET. 4:) "these phenomena depend only on the motion of the satellites and the position of Jupiter's shadow, and have nothing to do with, and can have no dependence on the position or motion of the carth.^^ On careful consideratioTi it becomes evident that this assumption is made to apply not only to the actual phenomena but also to the apparent phenomena as viewed from the earth . . . Is the assumption, so applied, wholly supported by the known circumstances belonging to the phenomena f If we first suppose the earth's place to be at that part of its orbit nearest to Jupiter, and, having there noted the apparent magnitude (angular magnitude) of that planet, we then suppose the earth removed to the opposite extremity of the orbit to the place most distant from Jupiter, and again note the apparent magnitude of that planet, it is manifest that, the distance of the earth from the planet having increased by about 190 million miles, the apparent magnitude of the planet, as seen from ihe earth, must have decreased proportionally. Has tiiis no particular relation to the phenomena, such as Lardner assumes that it has notf In the historical and descriptive statement of Roemer's discovery just quoted, it is stated in effect (1) that Roe- mer's computation of the times when the commence- ment of each eclipse was to be expected was made by taking the time observed to elapse between two succes- sive eclipses,* and multiplying that time by the number of eclipses included in the synodic period of the planet * At the time of writing his historical statement of the discovery Lardner seems to have been under the impressibn that Boemer had computed hia table from an observation taken when the earth was at or near to opposition, and that direct observation of the eclipse was then made, throughout the earth's revohition, from each 44 VILOOITY-OF-LIOHT THKORT. (Jupiter). (2) That as the earth receded from the planet, the actual commencement of the eclipse was later than the expected time given by the computation, and that this apparent retardation applied to each successive eclipse, so that the interval, by which the commence- ment of the eclipse was later, continually and regularly increased so long as the earth continued to recede from the planet. (3) That " as the earth again approached opposition, the difference became less and less, until, on arrival at E.^ the place of opposition, the observed eclipse agreed in time exactly with the computation." t Referring to the quotation from Herschel's Outlines, which will bo found in the Appendix, wc have the statement of that astronomer "when the earth comes to F., a point determined by drawing h. F. to touch the body of the planet, the emersions will cease to bo visible, and will tlienceforth, up to tlie time of the oppo- sition, happen behind the disc of the planet. Similarly, from the opposition till the time when the earth arrives at J., a point determined by drawing a I. tangent to the eastern limb of Jupiter, the immersions will be concealed from our view." And also, page 14 "It is to be observed that owing to the proximity of the orbits of the first and second satellite to the planet, both the immersion and emersion of either of them can never be successive part of its orbit. But, as shown elsewhere by Lardner him- self, such a supposition is inadmissible, because such direct observa- tions throughout a great part of the earth's orbit are not possible. It appears likely that Boemer obtained his average time, in the first instance, by dividing the synodic period of the planet into the number of the eclipses within that period, t Lardner's Astronomy. ' '. put n E \ vj ;! Tlat r VILOCITV-OF-LIQHT iniORY. observed in any single eclipse, the immersion being con- cealeil by the body if the planet be past opposition, the emersion if not yet arrived at it, so also of the occulta- tion The commencement of the occultation, or the passage of the satellite behind thedisc, takes place while obscured by the shadow before opposition and re-emer- gence after. All these particulars will be easily appa- rent on mere inspection of the Figure {See Appendix.') It is only during the short time that the earth is iti the arc G.II., i.e., between the Sun and Jupiter, that the cone of the shadow converging (while that of the visual rays diverges) behind the planet, permits their occulta- tions to be completely observed both at ingress and egress, unobscured, the eclipses being then invisible." These statements are quite in agreement with those of Lardner himself in his general exposition of the phenomena belonging to Jupiter's shadow and satellites. (See quotation, page 40. ^^ All these phenomena mani- fested at quadrature ; &c., «fec.") It is therefore quite apparent that the circumstances set forth by Lardner, as the result of Roemer's investiga- tion, in regard to the variation in the length of the intervals between the successive eclipses, are not facts of astronomical observation, but are obtained by computa- tion and inference from combined partial observations of the occultations and the eclipses. In the case of the two most distant satellites, when the earth is near qua- drature — whether it be receding from or approaching the planet — the commencement and the termination of the eclipses are both visible independently of the occulta- tions, but, with this exception, the times and circum- stances of the eclipse are inferred from the commence- 46 VELOCITY-OF-LIOHT THEORY. ment of the eclipse and termination of the occultation, or vice-versd. Now in legard to the variation in the apparent breadth of the planet's shadow as the earth approaches towards and recedes from it, it is quite true that no actual alteration takes place. The distance of the planet from the sun remains the same, and tlie dis- tance of the satellite from the planet the same as before, and if the satellite's immersion and emersion into a i d out of the shadow could be directly observed, those observations would not be necessarily vitiated or affected by the apparent variation in the size of the planet's shadow : For all the parts and distances of the parts irom each other, belonging to the Jovian system, including the planet itself and the planet's shadow, are similarly effected, and, increasing or decreasing in apparent size together, the relative proportions remain the same. But in regard to the occultation . . .let us carefully examine whether it may be safely concluded that the approach and recession of the earth towards and from the planet does not cause any variation in the time dur- ing which the satellite is hidden from the terrestrial observer ; or, to express in other words an equivalent conclusion, whether this approach and recession does not cause any variation in the angular quantity of the satellite's orbital arc cut off by the interposition of the planet : for if there be an arc sometimes of a greater and sometimes of a lesser angular magnitude taken out of the orbital circle, there will evidently be a temporal variation caused in tliat part of the satellite's revolution which is visible. Fig. 10 shows the planet, the orbit of the satellite, the planet's sha low, the sun, and the earth's orbit ; the earth w Orbit OcmvitaUon of Juj'iifcr's Snieiliie.. Fiq 10, \ il-. J t:a^ r ih m I* i I 1 VBLO(JirY-:>F-LiaHT THEORY. 4T is shown at opposition aad at conjunction ; at those two places, therefore, in the orbit, at which the eclipse of the satellite is entirely hidden from view, and the occul- tation is completely visible, that is, both the ingress and the egress of the satellite are visible. Now, by drawing the visual rays from the earth tan- gent to the disc of the planet, .namely, from the earth at opposition and from the earth at conjunction, it becomes at once evident that there is a difference : for the arc a. a. of the satellite's orbital circle intercepted by the planet when the earth is least distant, at opposition, has, manifestly, a greater angular magnitude than the arc I I. intercepted when the earth is most distant from the planet at conjunction. Is this difference noiv recognized hy astronomers f Are those compound observations, which are in part direct in respect to the eclipse, and in part direct in respect to the occultation, rectified relatively to this interfering circumstance ? Roemer does not appear to have regarded it ; Lardner does not mention it ; in Her- schel's treatise we do not find any reference to it what- ever ; nor have we met with any elsewhere ; but the difference is a necessary consequence of the varying distance of the earth, and calls for consideration and satisfaction ; it is a cause which must have its effect . . . how is that effect manifested ? -^ : ^ Let us go back to Roemer at the time of his first ascertaining the apparent variation in the interval between the successive eclipses . . to that time when he has just conceived and is about to propose the theory of . the velocity of light with the express purpose of account- ing for an observed effect to which he can assign no adequate known cause. We now find a cause which must 48 VELOCITY-OP-LIGHT THE0R7. necessarily have its effect, to wiiich no effect appears to have been hitherto assigned, and, moreover, a cause in kind and quantity precisely such as Roemer wanted to enable him to account for his observed effect. What ground have we for retaining the theory of the velocity of light ? It was notoriously suggested at first to supply a cause for a particular effect; and it was based upon that effect. . . .but since it now appears that that particular effect is claimed by another cause which has a primary right to it is there any other basis upon which the theory of the velocity of light may b''' supported ? We opine there is none other, and that the theory must be pronounced untenable, because unsup- ported by fact. Note. — It may therefore, be understood that the doctrine we afRrm is: — That the actual time of the satellite's revolu- tion is the time established by the direct observations of tho eclipse when the earth is near quadrature either east or west ; and that the commencement of tho eclipse is apparently later when the earth recedes further from the planet, and apparently earlier when the earth approaches nearer to tho planet, for the cause stated above and illustrated in tho figure, the partial observations of the eclipse being com- pounded with those of the occultation. Plate, Fig. 7, may serve as a general representation of the variation in the apparent scale on which the pheno- mena of the satellite's eclipse and occultation take place, according to whether it is viewed by the terrestrial observer from the earth's most distant or least distant place in its orbit. Fig. 8, which repeats a part of Fig. 7 on a larger scale, illustrates more especially the usual case of the eclipse compounded with the occultation. In ^ \ ? ! # "^ VELOCITY-OF-LIGHT THEORY. ■^' this (Fig. 8.) it is evident that the angle subtended by the arc contained between the outer edge of the shadow on the one side, and the visual ray touching the side of the planet on the other, is greater when the progress of the satellite into the eclipse and out of the occultation, is viewed from the earth at its place of least distance than when viewed from the more distant part of the earth's orbit. A circumstance worthy of attentive consideration is that, from the statement of the observed facts in regard to the variation in the time of the eclipse as given by Lard- ner (and which we believe is quite a correct statement of the case as now accepted by astronomers), there does not appear to be any serious difficulty in the way of sub- mitting Roemer's assumption to the direct test of astro- nomical observation : for, what is contained in that as- sumption ? That each revolution of the satellite when the earth is receding from the planet occupies a longer time than each revolution of the satellite when the earth is approaching {he planet ; and since the sum of the difference is 16 .ninutes, it follows that if the number of revolutions made by the sr.tellite in the »Synodic period of the planet be »«., the difference in time of the satellite's revolution will be 32' -^m, because when viewed from the one side of the orbit as the earth is receding the time of the period is the average period of (the satellite) increased hy l6'-i-)w, and on the other side of the orbit as the earth approaches opposition the time of the period is the average period less 16' -fm; the difference, therefore, is 32' -^w;. But this, again, is the average difference ; and evidently at or near the earth's quadrature, when the recession or ap- proach is more rapid, the difference would be greater. If VELOCITY-OF-LIOHT THEORY. we take the number of revolutions at about 190, the average difference in a single revolution, on the opposite sides of the orbit respectively, would be one-third of a minute, and if at or near quadrature, the difference would, perhaps, exceed half a minute.* Supposing, however, the difference on a single revolution of the satellite to be con- siderably less than this, it would still be a quantity of time which the practical astronomer can readily verify. This, then, is one of the distinct requisitions of Roemer's assumption which can be directly submitted to the deci- sion of experience. Let us now consider what effects would be necessarily consequent upon some very small quantity of time being occupied by light, in its communication from the sun to Jupiter, and from Jupiter to the earth. The quantity of time attributed by the theory (of the velocity of light) to a certain (definite) quantity of motion, seems to us less tluin reason authorizes tlie mind to accept as a (^reasonable) possibility ; or, in other words, the vei.^city attributed to light, by tliat theory, seems to us greater than is scien- tifically conceivable, keeping in mind that, by the theory, this velocity represents the actual progressive motion of ii variety or foiin of matter (/. e., of a material substance). To simplify the consideration of the subject, however, we will assume, for tlie moment, the possibility of such velocity, and suppose it to be S minutes for a distance of 100 million miles. We will take Jupiter's distance roughly " If tlie earth receded (an, VELOCITY-OF-LIOHT THEORY. 51 at 500 million miles, and thus we obtain at once a more distinct estimate of what the hypothesis involves; for instance, in respect to the entrance of the satellite into the shadow of the planet, as described by Lardner, the assump- tion of the theory is that the satellite enters the shadow of the planet in /ac< about 40 minutes (on an average) before it appears to us, viewing it from the eai th, to do so ; and hence, the eclipse must be far advanced before it appears to us to have commenced. Let us merely note here that this case is necessarily included in the assumption, and consider other conse- quents ; we will suppose the earth in its orbit, as shewn at^. a., Fig. 9, (Plate 9) with the planet Jupiter in oppo- sition, that is at the orbital place nearest to Jupiter. The earth then travels round to the opposite extremity of the orbit, into conjunction of that planet. If the planet were to remain motionless, this place in the earth's orbit would be B. in the Fig.; but, since Jupiter's augu- Jar velocity is about one-twelfth that of the earth, the planet will have moved through about 15' to M. / and the earth's orbital place of superior conjunction will be N. For the earth again to arrive at the place of opposi- tion of the planet, half the earth's solar orbit together with an additional 15° will be the distance required, and O. 0. will be the place of opposition ; M. 0. being equal to A. 31., and a. o. equal to twice B.N'., and in like manner P.p. will be the next place of conjunction, 0. P. being also equal to A. M. So that the distance from opposi- tion to conjunction is in fact equal to the distance from conjunction to opposition : but, on the assumption of the truth of the theory, will this actual equality in the dis- tances also hold good when the motions are observed from tm VELOCITT-OP-LIGHT THEORY. ihe earth ? Taking the earth at a., with the planet in op- position, and considering that, as the earth travels in its orbit towards N., the distance of the earth from the planet continually becomes greaterand, consequently, an increas- ing quantity of time is required for the light from the planet to reach the earth, we find that when the earth has arrived at N., this apparent increase in the time actually occupied will, by the theory, amount to 16 minutes. But now as the earth continues its progress, and returns towards opposition, the contrary effect must take place, and the like apparent quantity of time be gained. Th6 result must, therefore, be, if we compare the two halves of the entire synodic revolution of the earth, a difference of 32 minutes. But, moreover, this semi-orbital diffe- rence, as measured by time, which belongs to the theory, is not peculiar to the planet Jupiter: it is equally applicable to any other superior planet, because the distance we are here considering is that of the diame- ter of the earth's orbit. Therefore we have to ask whe- ther there can be a difference in time of about 32 minutes between the two halves of the synodic revolution in the case of eacli superior planet, which has never yet been observed, or which, in other words, has hitherto escaped the observation of all astronomers ? {NoU. — It is undesirable in this place to complicate the subject by investigating the additional effect which would arise, under the hypothetical conditions of the case, in con- sequence of the reversed direction of the eurth's orbital motion at opposition and at conjanction respectively. It will bo sufficient to observe that, at opposition, light from the planet would, according to the theory, require about 36 minutes- to reach the earth which would be then moving from east. ' yiLoornr-oF-LioLTT thbobt. Of to west ; and at conjunction, about 52 minutes, when the earth would be moving from west to east) But let us consider the case of an inferior planet; take, for example, the planet Venus. Now, there is this difference between the case of an inferior and that of a superior planet ; that, when the former is in inferior conjunction the solar light passes the planet and comes directly to the earth. When, however, the inferior planet is in superior conjunction, the case is similar to that of the superior planet, and the light of the sun going first to the planet is reflected therefrom to the earth. Herein we observe another favorable opportunity to submit the fundamental assumption of the velocity-of- light theory to the test of fact ; for, fhe transit of Venus furnishes the moment of inferior conjunction almost in- dependently of the velocity hypothesis,* the solar light at that time having a distance of only about 26 million Miles to reach the earth, which distance, by the theory, would require a little more than 2 minutes; whereas, at superior conjunction the distance of Venus from the earth is about 1G5 million miles, requiring by the theory about 14 minutes ; a difference in time there- fore of about 12 minutes. Let us therefore ask the practical astronomer for a decided answer on fact as to whether the planet Venus takes 24 minutes longer to travel from inferior to superior conjunction than it tivkes ♦ I ,. *; i • Because the supporters of the tlieory expressly reject the testiuiony of sight as evidencing that what appears to take place at a certiin time does actually take place at the time. We are told. . . No : your sight deceives you ; you are reading only the reconl of the past; whi.t appears to you to be now taking place has in fact taken place some time since. ^^m f^mmm. 64 YILOCITT-Or-LIOBT THXOBT. to travel from superior to inferior conjunction .... For it is a requisition of Roemer's assumption that there shall be such difference, and if astronomical observation shows that there is no such difference . . then fact is against the assumptioii. The combined eclipse and occultation of Jupiter's second satellite viewed from the first satellite ; supposing the latter (the first satellite) to remain stationary. The second satellite is seen enterbg the western side of the shadow at a, aqd is again seen emerging from htUnd the eastern limb of the planet at b. : I « LIGHT. We have now examined carefully and attentively those two comprehensive theories of light which have succes- sively received the approval and concurrence of men of science. Of the two theories of the nature of light, Newton's cor- puscular or emission theory, which is the oldest and most definite of them, has been given up and discarded in favour of the undulatory theory. These two theories, although, in many respects, differing widely from each other, are both founded on an assump- tion that light is in its nature material that it is either a variety or peculiar description of matter, or else^ a dynamical manifestation of matter. By the on& theory, a particle of the peculiar matter leaving the luminiferous body by which it is emitted, travels onward in a right line until it comes in contact with the recipient, and the impact of the material particle upon the material body produces the effect termed light. By the other theory a material fluid is supposed, and the effect is con- veyed and communicated by means of the material particles of this fluid : a wave, vibration, or impulse, commencing at the luminiferous body, is propagated through and by means of the material particles of the fluid ether, and, again, there is impact, by matter in motion upon the material body of the recipient, occasion- ing the effect termed light. By either theory, therefore, time is necessarily occupied in the communication of the - ; r)6 THEORY AND LIOHT. light from the emittent or luniiniferous body to the reci- pient, .the particles, or the vibrations leave the emittent body, they move through successive spaces, and they nrrive at the place of the recipient. Both theories, therefore, belong in common to a primary velocity-of- light hypothesis or theory, and it is as to the reality of the basis upon which this fundamental hypothesis is sup- posed to rost and upon which the entire superstructure is dependent that the concluding part of our investigation has been directed. The supposed facts (of observation^ upon which the velocity -of-light hypothesis is based, and upon which it is primarily altogether dependent, are three. Of these, the oldest and by far the most important (and which is, indeed, generally looked upon as being alone the funda- mental and sure support of the theory), is Roemer*s observations of the eclipses of Jupiter's satellites. We have now shown, with respect to those observktions, that the velocity-of-light assumption, adopted to explain the rariation in the apparent period of the satellites, is a mistake which has arisen in the omission to appreciate the variation in the visual angle occasioned by the increase and decrease of the earth's distance from the planet. ..• • ,...; The second of thi supposed facts is the so-called aherration of light. t has been now shown that the reasoning which attributes certain natural phenomena to such suppositious cause is unsound, and that the aber- ration theory is merely notional without actual support of fact. It is therefore unreal. The third supposed fact is the result of certain experi- ments with Wheatstone's reflecting apparatus. But the T'-^ ^. THEOHT AND LIOHT. 57 result of these experiments as evidence on the primary question, viz., whether light has velocity, was assumeil therein ; and the actual question which the enquirer proposed thus to submit to experiment, to be answered and determined, was — what is the quantity or amount of the velocity?* If it be assumed, on the contrary, that light has no velocity, an experiment with an apparatus of this des- cription similarly conducted would, nevertheless, give an apparent velocity as the result, according to the .lumber of reflectors employed ; because the light leaves the last reflector subsequently to its leaving the reflector next before it, and, again, it leaves that one subsequently to the one next before that, and so on ; and, therefore, in a series of reflectors, a certain time would be occupied in the transmission of the light from one reflector to the next.t It is true the result of the experiments with this 'That is to say. time would be occupied in the act of reflection, not in the communication of llie light from the surface of the one reflector to the surface of the next. tin thus stating the question, submitted to experiment, we are according to our view, extending rather than lessening the significance of the questioa actually submitted. The question submitted was practically . . Is that amount of velocity already established exactly cor- rect ? The con viction (prej udice) in the minds of those submitting the question being not only that a velocity was established, but that the quantity of velocity had been ascertained either with precision or with a dose approximation thereto. In all probability more than a slight discrepancy in the result, from what it was already decided that re- sult must be, would have condemned the apparatus as being in some way unsuitable for the experiment. , THE NATCRB OF LIGHT. apparatus is stated to have been in close agreement withr the velocity which had been previously fittributed to- light ; but, when we consider that such an agreement^ even if the experiments were conducted with scrupulous precaution and care, might be quite fort. litous, and when we consider, also, that the experiments were undertaken with a foregone conclusion or prejudice of so strong a character that it might be called a conviction, (i.e., an unsound conviction,) not only as to a velocity but also us to the established quantity of that velocity, we cannot allow that these experiments, viz., with Wheatstone's^ reflecting apparatus, standing alone and unsupported, which they now do, are entitled to be considered as fur- nishing evidence of value in any degree in regard to the primary question. Since, therefore, it has been now shown that the several theories, which attribute a material nature to light (meaning thereby the influence which occasions light),are, each of them severally, and all of them collectively, un- souiid and consequently untenable ; and since it has been also shown that the supposed facts of observation, by which the velocity attributed to light was considered to be established, are, in that sense, illusory, and do not, in fact support such conclusion, we are thrown back upon the primary question. is light material f .Now if light be material in its nature, it is certain that time must be occupied in its transmission ; and, inverting the proposi- tion, if no time is occupied in its transmission, then it is certain that light is not of a material nature. To answer the question in this fonii we have the positive evidence of Roemer'e observations, confirmed by all later obser- vers, of the eclipses of Jupiter's satellites. This is, ^i I THE NATCP.E OP LIGHT. 59 perhaps, the only positive (direct) evidence* which can, at the present moment be put before the rendoi us fact demonstrated by direct observation, and as, therefore, indisputable: but it is, we opine, entitled in itself to be considerad conclusive ; for the distance of the planet Jupiter ia so great that, as already stated, any conceivable velocity of a material substance or of an influence trans- mitted by means of a material fluid (or any description of matter) would necessarily occupy a very appreciable quantity of time in travelling from that planet to the earth : consequently, since it is established by astrono- mical observation that no appreciable quantity of time is occupied in the transmission from the planet Jupiter, the evidence is positive and decisive that light has no velocity. Wherefore we conclude that the evidence in fad is sufficient to answer demonstratively the primary question; and the answer to that question is accordingly — that the nature of light (meaning thereby the influ- ence which occasions light) is sjtiritual, and not material. Assuming that the conclusion just stated, in regard to the primary question, is sound ; let us now see what secondary conclusions of an important character will follow as corollaries or consequents tliereto. For this purpose it will be convenient to take physical \ I * There is much negatice eviilence, poine of wliich we liave alluded to, or indicated. Theoretical considerations are, we opine, in the present state of knowledge, it' the mind be freed from the prejudice occasioned by tlie undulatory and otiier tiieories, altogether opposed to the idea of light having velocity. If, for exuinple. such u supposi- tion be entertained, it immediately apjH'ars to lolluw that interfer- ence and confusion, occasioneil by liglit arriving at tlie same time from a number of ditlerent objects, would iieceasaiily take place. THE NATURE OF LIQUT. science, or that division of physical science to which the phenomena of light and sound belong, and to put these conclusions in the form of a brief generalization, making use of certain of the recorded facts, and a part of that common knowledge belonging to the subject, which may be considered certified by science at the present time. The Physical Forces of Natural Science. Force is that which causes a change in the condition of matter, overcoming a resistance (antagonism or oppo- sition) ; which resistance is equal in amount to the quan- tity of force ex ed. Force is k.iown to us as manifested in several forms or conditions (modes), differing from each other and having its act'.ve energy in each condition controlled by definite and distinct laws, which, having been more or less investigated, are now in some measure known. The several forms or modes of force, now recognized as acting on the material world, and distinguished each from each by the effects on matter of its manifes- tations, definite and different in the one particular form from those in each of the other forms, are Forms of Force. Forces ( Voluni Electric Force. < ( Light. Manifestations of Force on Molecular Matter. Volumetric Electricity. Light. Heat. Magnetic Force. Molecular (Voltaic) Elec- tricity. Acoustic Force. 5 Sound. Manifestations of Force on Aggregated Matter. Dynamic Force. B'orce •< Motion of Material bodies. Mechanical effect. ( Mechanical effect. Gravitative Force. < ( Weight or Gravity. €2 FORCE AND MATTER. All change in the material world is the result of a mani- festation o{ force. The primary or general law under which all the fonns or conditions (modes) of force are manifested and become cognizable by us is that of suc- cession. The successive manifestations of force, that is, its mea- surement by the successive effects of its manifestations on matter is known to us as time.* Distance is the quantity of separation (i.e., inter>\ining space) between definite localities at which manifestations of force upon matter are cognized. Force is, therefore, not material l)ut sinritiial. Since the cognition of the material world (i.e., of matter) by the spiritual being, is in ourselves a manifestation or result oiforce-eneryy acting on matter, we cannot divest ourselves of the irfea of «e in cognizing matter except in the case of a simple sensation, because the succes- sive recognitions of the successive eflects is that which we mean by the expression ' idea of time.' But matter itself, in its simple elementary condition, separated from force, is only indirectly known to us. Chemical science teaches us to indirectly recognize the fact that such simple elementary matter is existent +, but it has not been, neither can it ))e, directly cognized by us apart from its spiritual adjunct /o/ce. * This may bs familiarly illustrpted by reference to the dial-plate of a clock, where the motion of the hour-hand measures the successive vibra- tions of the pendulum. The measurement m»y '-wl oT (cognized) in hours, minutes, or seconds, but it is alwuv; ? mjai^nrewi-at fr ^ a definite starting point (zero-point), and it expressea iht co. ecti'.e cosf.iUio.T of the successive vibrations \rhichhave taken place t. 'nsv^ueni i tl.ai.; ;at. t But to aitutne that chemical evidence, as set TortL icfuo atomic theory, makes us acquainted with simple elementary matter sf '•nted from /orcf is, perhaps, to assume (i.e., to include the assumption' that natter itself is primarily a materialized (fixed) condition or mode of ^^gravitativc) force. FOBCE AND MATTER. # Therefore all the forms or varieties of compound matter i^nown to us, are compounded of {the spiritual and the material) force and matter. And, also, by an addition to or a deduction from the quantity oi force contained in a particular form (variety) of matter, the physical condition of that form of (com- pounded) matter may undergo a change. . although its essential form as distinguished from other fonns of (com- pounded) matter remains unaltered: ... as, for example Nv.iter, which by the addition or deduction of that form of force known as heat, assumes accordingly the con- dition oi steam or of ?co, in either of which conditions it still remains essentially the same form or variety of (compounded) matter — vi/., water, m distinguished from all other varieties of mattt;r. Force in combination with matter may be considered Aonxiwniox latent ; the energy of the force may be said to be employed (in resisting change) in preserving the ex- istence, condition, and form of the compounded matter ; it has been (so to speak) materialized, and has become (temporarily) a part of the compound matteir ; but, if the equilibrium of the compounding elements of the body be disturbed by addition or interference of (other) force, the condition, or, it may be, the compounded form, of the body must undergo modification or decomposition, and a certain quantity of force, exactly proportional to the quantity of matter acted upon and changed, is set free to manifest its energy as active force, by combining with or disturbing the conditions of, other forms of compounded matter. Herein we have particular sources of force or of mani- festations of force-energy within the material world, 64 FORCE AND MATTER. % as known to us. It may be said that the source of all the force-energy usually recognized as belonging to the material world is such a disturbance of existing com- pounds or combinations, and the consequent setting free of force previously latent or inactive, in the com- pound. Sidereal (solar) force may be, however, consider- ed as, to some extent, a possible exception* i.e., as, possibly, including an outside source ; because, although there is strong probabilility that the active or free force thence derived ' the result only of a continuous regu- lated (material) disturbance of the same character, and that the sun may be correctly understood to act as a re- servoir of force, continually collecting and redistributing a regulated supply — nevertheless we cannot be quite sure, in the present state of knowledge, that sidereal (solar) force may not include a more distinct manifesta- tion of outside t spiritual energy, in which case solar force would have have to be looked upon as the primary J source of terrestrial force ; whereas, otherwise, i.e., as- suming *Le sun to be simply the central recipient and dis- tributor of active force — all terrestrial (or planetary) and solar manifestations of force must be looked upon equally as parts of that collective quantity of force belonging to the solar system. * If it be assumed that the Aggregate quantity of compound matter in the universe undergoes increase, i.e., that a manifestation of Creative energy is continully or occasionally tuking place, a propor- tionate addition to the collective quantity of force would be, perhaps, necessary, and (it is meant that) the sun, or other central star, may possibly be the medium through which such additional quantity is supplied. t Meaning thereby ... a source outside that which is known to us as the material universe. t That is — primary, in a merely terrestrial sense. Allied Forms of Force According to the Eecord of Physical Facts. A reference to the record of observed facts will show the close relationship of volumetric (frictional) electricity and light. (Note. — It is necessary to remark that certain unde- monstrated theories or mere assumptions have been allowed in some cases to mingle with the recorded facts in such wise as to necessitate considerable caution ; for example, the theory or assumption of two electricities, or two kinds (varieties) of electricity, having characteristic properties, in some respects directly opposite in the one kind from the corresponding characteristic properties in the other. It was early objected to such assumption that it was superfluous and undemonstrated (unsup- ported), and a sort of compromise was effected in regard to the nomenclature, by calling the (supposed) one kind positive, and the other ymjativc electricity. Since that time, however, the illegitimate influence of theory has been still further allowed to usurp the legitimate autho- rity of science, ano it seems to be now almost forgotten that the two electricities, or two kinds of electricity, is a mere hypothesis unsupported excepting by a certain superficial appearance of probability which would equally apply to a supposition of ' coldness' being a variety of form of * heat ' ; that is to say, to an assumption of two ' heats ' or two kinds (varieties of heat), in which certain of the characteristic properties of the one would be the opposite to the corresponding characteristics of the other.; 4t eleotricitt and liout. Volumetric Electricity and Light. Encjclopedia Britannica. Art. Electricity. Part 1. Sect. V. — On the Electric Spark. "Since the discovery of electric light by Otto Guerick nnd Dr. Wall, the subject has attracted the particular atten- tion of philosophers. In exciting a glass tube, or in work- ing an electrical machine in the dark, sparks and streams of light are distinctly visible ; but the phenomenon is best eeen when the knuckles or a brass ball is brought near to an electric conductor. A bright light, .^allod the electric spark, passes from the conductor to the knuckle or ball, and exhibilN a groat variety of phenomena, varying with the nature and intensity of the olectricitj', and with the form, magnitude, distance and nature of the l)odie9 between which it passes. Exp. 1. — Having screwed into a prime conductor a brass ball about two inches in diameter, and projecting about three inches, electrify the conductor positively, and hold another ball near tlie fii'st. Long ramified zig-zag sparks will j^ss between the two balls, as shown in Fig. 6, (Pi. 10,) where pos. is the positively electrified ball, and nat, the one hold in the hand in a natural stale of electricity. If the ball on the conductor is very small, the spark will become a faint divided brush of light. If the ball on the conductor is elec- trified negatively, the spark will be as shown in Fig. 7, (PI. 10.) clear, straight, and more luminous. If one of the balls is positively, and the other negatively electrified, the forms shown in. Fig. 6 and 7, will bo combined as in Fig. 8. When, in this last experiment, the distance of the balls is rot too great, the positive zig-zag ppark will strike the nega- tive straight spark about one-third of the length of the latter from its point, the other two-thirds becoming very lumin- ous. Sometimes the positive spark strikes the negative •Imll at a distnnce from the negative spark. Exp. 4. — Hold an insulated sheet of paper at a small dis- Htl If w w ELECTRICITY AND IKiHT. 67 ■"tnncofVom a positively olottrified conductor, and n boftutiful Htur with dintinct radiatioos will bo thrown ujxn the poper. If tho conduitor in utx^ativoly electrical, a cone of ray-^, with itH Itaso {^\\ tho |i«|»v)r and it.t apex on tlii' conducts*, will rqtiaco tl>o ntar ExfK B. — If the point of a noodlo is pros^i .-d to a j,«/>!»itively cloctrifl«Ml »'on\lmtorin thudark, the point will be illnnunated with a Ktar; but if tho conductor i^ imjative, the needU; will exhibit a pencil or bruxh of light* Tlio following experiment illustrates the offcct ofdistance on tho spark. Krp. 6. — Fix a sharp-pointed wire to the end of the prime conductor, and having electi'irt»'i it positively, hold an insuU nted ball of metal very near the metallic point; a succes«i'>ii of small and hriUiantly white sparks will jias!* between liieni. Tho '.vhite colour will tend to red an the distance of the ball and tho point is increased, and at a certain di.^tanoc the sharp explosions will cease, and a ff«>ble violet light will diverge fr^m tho extremity of the puint, covering with its base the nearest half of the sphere. The influence of the form of tho bod}' upon the spark ■which it giv( •< is considerable. Professor Hildebrand, of Krlang, found an obtuse cone with an angle of 52° gave a much more luminous spark than one with an angle of 30°, and ho found that the parabolic rounding of the summit, or slight inequalities of the surface, are particularly advant- ageous in the production of a stntng light. The i>:fluence of points on the spark has been already described. Tho nature of the IxKly by which the spark is taken exercises also an influence upon its magnitude and its colour Pro- fessor Hildebrand made some interesting t .<)i(.'rimenis on this wubjoct. The pie'cs of metal had a conical form. an time, according to what has been explained (1785), the fluid on A. accumulates on the side next to B. These two tides of electricity of opposite kinds exert a reciprocal attraction, and nothing prevents them from rushing together and coalescing, except the pressure of the intervening air. They will coalesce, therefore, as soon as their mutual attrac- tion is so much increased as to exceed the pressure of the air. This increase of mutual attraction may be produced by several causes. First, by increasing the charge of elec- tricity upon the conductor A., for the pressure of the fluid will be proportioual to its depth or density.* Secondly, by diminishing the distance between A. and B., for the attraction increases in the jame ratio as the square of that distance is diminished ; and, thirdly, by increasing * Herein may be remarked the (perhaps unintentional) expression of a . coftclusion or prejudice to the effect that the electric influence (force) is a material fiiiid, and consists of particles which gravitate. If this be not the intended meaning. . . why not have written ' proportional to the quan- tity ?' Some writers on electricity thus use the term ' fluid' (electric fluid) with a sort of protest that they are not to be understood as defining or denoting the character of the influence. They nevertheless use it ; and every one is familiarized with the idea of an electric-:/2ut(;( passing or flowing in a current through a conductor. Thus we have an illustration of some of the consequences of introducing definitions into scientific nomenclature based on vague conjecture. The supposition of the two electricities will not, we opine, be found to be supported by fact ; yet it is not, in the exist- ing state of scientific knowledge, unreasonable, and may be considered, for tba moment at least, tenable, and therefore a scientific theory. The assump- tion of that theory is the existence of two electricities — that is, of two posi- tiva electricities having certain different and opposite characteristics; and one of these two positive electricities is called negative electricity. The other case (the misuse of the term^uii) is, however, much more seriously objectionable ; and the supposition therein embodied, if formerly considered to belong to science, has become long since untenable, being contradicted by many of the now well-known facts pertaining to the subject. . , , , • F ' ' L_ ™ ■;,'■■ "" if ■■ '-'^Kti tur. » '74 BLECTRICITT AND LIGHT. ■" the conducting power of either or both of the bodies A. and B., for by that means the electric fluids, being more free to move upon them, will accumulate in greater quantity on the sides of A. and B. which are presented towards each other. Fourthly, by the form of the bodies A. and B., for according to what has been already explained (1776),* the fluids will accumulate on the sides presented to each other in greater or less quantity, according as the form of those sides approaches to that of an edge, a corner, or a point. When the force excited by the fluids surpasses the sus- •laining force of the intervening air, they force their passage 'through the air, and, rushing towards each other, combine. This movement is attended with light and sound. A light appears to be is produced Lotween the points of the two bodies A. and B., which has been called the electric spark, and this luminous phenomenon is accompanied by a sharp sound like the crack of a whip." (1812.) " The Electric Spark. — The luminous phenomenon • called the electric spark does not consist, as the name would Fig. 11. imply, of a luminous point which moves from the one body to the other. Strictly speaking, the light manifests no pro-, gressive motion. Itconsists of a thread of light, which for an instant seems to connect the two bodies, and in general is not extended between them in one straight unbroken direction, like a thread which might be stretched tight be- tween them, but has a zigzag form resembling more or less the appearance of lightning. (1813.) " Electric aigrette.— U the part of either of the bodies A. or B. which is presented to the other have the form of a point, the electric fluid will escape, not in the form * See page 88, et teq. ELECTRICITY AND LIGHT. w *" of a spark, but as an aigrette or brush light, the diverging rays of which sometimes have the length of two or three inches. A very feeble charge is sufficient to cause the escape of the fluid when the body has this form." (1814.) " The length of the spark.— If the knuckle ot the finger or a metallic ball at the end of a rod held in the hand be presented to the prime conductor of a machine in operation, a spark will be produced, the length of which will vary with the power of the machine. By the length of the spark must be understood the greatest distance at which the spark can be transmitted. A very powerful machine will so charge its prime conductor that sparks may be taken from it at the distance of 30 inches." (1815.) " Discontinuous conductors produce luminous effects. — Since the passage of the electricity produces light where- cver the metallic continuity, or, more generally, wherever the continuity of the conducting material is interrupted, these luminous effects may be multiplied by so arranging the conductors thtit there shall be interruptions of continuity arranged in any regular or desired manner." (1816.) " Experimental illustratim.— If . a number of metallic beads be strung upon a thvead of silk, each bead be- ing separated from the adjacent one by a knot on the silk so as to break the contact, a cux'rent of electricity sent through them will produce a series of sparks, a separate spark being produced between every two successive beads. By placing one end of such a string of beads in contact with the con- ductors of the machine, and the other end in metallic com- munication with the ground, a chain of sparks can be main- tained'so long as the machine is worked." (1817.^ "Effect of rarefied air. — When the electric fluid passes through air, the brilliancy and colour of the light •evolved depends on the c" jnsity of the air. In rarefied air the light is more diffused und less intense, and acquires 76 ELECTRICITY AND LIQHT. " a reddish or violet colour. Its colour, however, is affected^ Bb has been jast stated, by the nature of the conductors be- tween which the current flows. When it issues from gold the light is green, from silver red, and from tin or zinc white;, from water yellow inclining to orange. It is evident that these phenomena supply the means of producing electrical apparatus- by which an infinite variety of beautiful and striking luminous effects may be pro- duced. When the electricity escapes from Fig. 12 a metallic point in the dark, it forms aa aigrette, Fig. 12, which will continue to be visible so long as the machine is worked. The luminous effect of electricity on rarefied air is exhi- bited by an apparatus. Fig. 13, consisting of a glass recei- ver, b.b.', which can be ecrowed upon the plate of an air- pump and partially exhaurted. The electric current passes- between two metallic balls attached to rods, which slide in. air-tight collars in the cover of the receiver b.b'. Fig. 13. It is observed that the aigrettes formed by the negative- fluid are never as long or as divergent as those formed hy the positive fluid, an effect which is worthy of attention a» indicating a distinctive character of the two fluids."* (1828.) " Experimental imitation of the auroral light — Thi* 1 henomenon may be exhibited in a still more remai'kable^ » yes ; if we suppose two distinct kinds of electricity ; but, if there be- only one, the explanation may be thus stated:— (1.) The electricity- entering at 6.', diverges from that ball. (2.) The electricity having been, removed from the ball at 6. , an equivalent quantity is attracted or gravi- tates thereto. ' - ' V" i ELECTRICITY AND LIGHT. 77 m •" manner by using, instead of the receiver 6.6'., a glass tube two or three inches in diameter, and about thirty inches in length. In this case a pointed wire being fixed to the inte- rior of each of the caps, one is screwed upon the plate of the air-pump, while the external knobs of the other is connected by a metallic chain with the prime conductor of the electri- cal machine. When the machine is worked in the dark, a succession of luminous phenomena will be produced in the tube, which bear so close a resemblance to the aurora borealis as to suggest the most probable origin of that •meteor. When the exhaustion of the tube is neany perfect, •the whole length of the tube will exhibit a violet red light. If a small quantity of air be admitted, luminous flashes will be seen to issue from the two points attached to the caps. As more and more air is admitted, the flashes of light, which .^lide in a serpentine form down the interior of the tube, will ^become more thin and white, until at last the electricity will cease to be diffused through the column of air, and will appear as a glimmering light at the two points." (1819.) " Phosphorescent effect of the spark.—Tho electric spark leaves upon certain imperfect conductors a trace •which continues to be luminous for several seconds, and -sometimes even so long as a minute after the discharge of the spark. The colour.of this species of phosphorescence varies with the substances on which it is produced. Thus white chalk produces an orange light. With rock crystal the light first red turns afterwards white. Sulphate of i)aryta, amber and loaf sugar render the light green, and ■calcined oyster-shell gives all the prismatic colours." (1822.) " Electric light above the barometric column. — The electric light is developed in every form of elastic fluid and vapour when its density is very inconsiderable. A remarkable example of this is presented in the common barometer. When the mercurial column is agitated so as lit fll 91 ELICTRICITT AND LIGHT. Fig. 14. " to oscillate in the tube, the space in the tube above the col- umn becomes luminous, and is visibly so in the dark.* Thi» phenomenon is caused by the effect of tho ■ electricity developed by the friction of the mercury and the glass upon the atmosphero of mercui'ial vapour which fills the space above the column in tho tube." (1823.) " CavendisKs electric barometer . — The electric barometer of Cavendish, Fig. 14, illustrates this in a striking manner. Two barometers are connected at the top by a curved tube, so that the spaces above the two columns communicate with each other. When the instrument is agitated so as to make tho columns oscillate, electric light appears in. the curved tube."* (1824.) " Luminous effects produced by imperfect con- ductors. — The electric spark or charge transmitted by means of the universal discharger and Leyden jar or battery through various imperfect conductors produces luminous effects which are instructive. Place a small (melon, citron, apple, or any similar fruit on the stand of the discharger; arrange the wires so that their ends are not far asunder, and the moment when the- jar is discharged the fruit becomes transparent and lumin- ous. One or more eggs may be treated in tho same manner if a small wooden ledge be so contrived that their ends may just touch, and the spark can be sent through them all. Send a charge through a lump of pipe-clay, a stick of brim* stone, or a glass of water, or any coloured liquid, and the- entire mass of substance will for a short time be rendered luminous. As the phosphorescent appearance induced is by *We would note this experiment as particularly valuable on the assump- tion tbit h?reiD we have the coaversion of one form of electric force... namely, motion or mechanical effect, into another form . . . namely, light. ZLECTBICITY AND LIOBX. 7^ " no means powerful, it will bo necessary that these experi- ments should be performed in a dark room, and, indeed, the effect of the other luminous electrical phenomena will be heightened by darkening the room. n827.) " Cracking noise attending electric spark.* — The sound produced by the electric discharge is obviously ex- plained by the sudden displacement of the particles of the air, or other medium through which the electric fluid passes."" THE LUMINOUS TRAIN OF THE COMET. Returning now to the required explanation as to the luminous train of the comet (see conclusion of Part Fourth), let us again state the actual circumstances,, such as we found reason in the previous examination of the case to believe them to be . . . namely, circum- stances more or less similar in character to those of the primary condition of the earth. (Part Fourth page 12.) "The spherical mass of matter in a liquid (molten or fluid) state, occupying the central part of the body,, covered by the solid crust in an intensely heated condi- tion, and surrounded by the vaporous and gaseous en- velope, would give the appearance of the ' nucleus ' and the ' coma.' Now, if we suppose a quantity of free electricity (/.^., uncombined electric-force in the form of volumetric electricity), belonging to the cometary-mass of mat* ir, to be in a state of disturbance, it is evident from \ hat has been put before the reader that herein ♦ It will be understood tbat we do not consider the undulatory theory of sonnd to be longer tenable. It does not, however, follow, because air is not the cause or orif^in of sound, that, therefore, air does not conduct sonnd ; on the contrary, the evidence, we opine, is conclusive that air does con- duct sound . . . tbat is to say, conducts that form of Force which occasions thtefftctcsMeiaouni.— See Second Division. 80 ELECTRICAL INDUCTION. we should have a cause of a luminous appearance. Are the circumstances, such as we have stated favourable to tlie supposition ? Certainly, they are very favourable; because, since free elec .'icity is readily convertible into that form of electric -force culled ' heat,' as, for example, when an imperfect conductor such as a wire is heated and fused by electricity, so is free (active) heat readily convertible into free electricity. It is also apparent that the circumstances known to be favourable to the produc- tion of free electricity in the earth's atmosphere... namely, a high temperature of the earth, and a vaporous condition of the air, would be, in the case supposed, far more effec- tive, in consequence of the very high temperature of the solid matter of the comet and the highly vaporous con- dition of the comet's atmosphere. What would be the probable effect of the sun's influence on a planetary mass (i.e., a comet) in such condition? We shall now show by reference to the observed facts that the probable effect would be to drive the free electricity to that side of the comet opposite to the sun, where it would accu- mulate, and by which accumulation of electricity, sup- posing the quantity of it to be very great, the observed appearances of the luminous train would be produced. •For the record of the observed facts we will refer to the same two writers as before. ELECTRICAL INDCCTIOX. Encyelopedia Britannica* Chap. I, Sec. XII. — " On Electrical Induction, or the decomposition of the combined Electricities by actions at a distance.— In the preceding sections we have considered the phenomena of electricity as produced by friction, and as communicated or transmitted by conductors to other bodies. But it has been found that electricity may be developed in bodies by the mere influence of • Sir David Brewster. ILKCTRICAL INDUCTION. •i " an electriflcJ bcxiy placed ata If the sides of a flat plate of sufiicient thickness be rounded, the accumulation of fluid at the edges will be diminished. .[,;;,/; ,? The depth of the fluid is still more augmented at corners where the increase of depth due to two or more edges meet and are combined ; and this eflect is pushed to its extreme limit if any part of a conductor have the form of a ^oini. * The pressure of the surrounding air being the chief, if not the only force, which retains the electric fluid c a conductor, it is evident that if at the edges, corners, or angular points, the depth be so much in- creased that the elasticity of the fluid exceeds the restraining pressure of the atmosphere, the electricity must escape, and in that case will issue from the edge, corner, or point exactly as a liquid under strong pressure would issue from a jet d'eau." (1777.) " Experimental illusiraiion of the effect of a point. — Let F. (Fig. 609) be a metallic point attached to conductor C, and let the 'f^ TOLITMITRIC ILEOTRICITT. 89 perpendicular n. express the thickness or density of the electric fluid at that place; this thickness will increase in approaching; the point P. so as to be represented by perpendiculars drawn from the respective points of the course n.n.n." to A. P, so Fig. 509. '^*** '^^ density at P. will be ex- pressed at the perpendicular n" . P. Experience shows that in ordinary states of the atmosphere a very moderate charge of electricity given to the conductor C. will produce such a density of the electric fluid at 4he point P. as to overcome the pressure of the atmosphere, and to «au3e the spontaneous discharge of the electricity. The following experiments will serve to illustrate the escape of electricity from points : Let a metallic point, such as A. P., (Fig. 509,) be attached to a conductor, and let a metallic ball of two or three inches in diameter, having a hole in it corresponding to the point P., be stuck upon the point. If the conductor be now electrified, the electricity will be dif- fused over it, and over the ball which has been stuck upon the point P. The electric state of the conductor may be shown by a quadrant electrometer being attache', to it. Let the ball now be drawn off the point P. by a silk thread attached to it for the purpose, and let it be held suspended by that thread. The electricity of the conductor C. will now escape by the point P., as will be indicated by the eleclro- meter, but the ball suspended by the silk thread will be electrified as before." (1778.) Rotation produced by the reaction of points.— Let two wires A. R and CD., (Fig. 510) placed at right angles, be supported by a cap E. upon n fine point at the top of an insulat- ing stand, and let tiiem communicate by a chain F. with a conductor kept constantly electrified by a machine. Let each of the four arms of the wires be terminated by a point in a horizontal direction at right angles to the wire, each point being turned in the same direction, as represented in the figure. When the electricity comes from the conductor to the wires it will escape from the vires at these four points respectively ; and the force with which it O Fig. 610. ' VOLUMETRIC ILICTRIOITT. leaves them will be attended with a proportionate recoil,* which will cause the wire to spin rapidly on the centre E. (1779.) " Anothtr experimental illustration of this principle.— An apparatus supplying another illustration of this principle is repre- sented in Fig. 511 ; a square wooden stand T. has four rods of glass inserted in its corners, the rods at one end being less in height than those at the other. The tops of these rods having metal wires 4 . B. and C. D. stretched between them, across these wires another wire E, F. is placed,, having attached to it at right angles another O.H, having two points Fig. 511. turned in opposite direction at its extremities, so that when 6, H. is horizontal these two points shall be vertical, one being presented upwards and theotherdownwards. A chain from B. communicates with a conductor kept constantly elec- trified by a machine. The electricity coming from the conductor by the chain, passes along the system of wires and escapes at the points G. and H. The consequent recoil causes the wire G. H. to revolve- round E. F. as an axis, and thereby causes E, F. to roll up the- inclined plane." (1794.) " Curiaus effect of repulsion of pith ball. — Let a metallic point be inserted into one of the holes of the prime conductor, so that,, in accordance with what has been explained, a jet of electricity may^ escape from it when the confluctor is electrified. Let this jet, while • It may be well again to remind the reader of the hypothesis of aa imponderable but material fluid ... a hypothesis scientifically inadmissi- ble, but which Dr. Lardner appears to have practically accepted. Dis- allowiag that hypothesis, it does not quite follow that the electric force, being spiritual, may not or might not have an action on the particles ot' air such as seems to be here indirectly attributed to it ; we opine, how- ever, that the evidence is quite insuflScient to substantiate such conclusion. If the effect is recoil in the material and usual sense, the case is one of action and reaction. Evidently the air should have motion imparted to it.. Is there any evidence of such e£fect7 Let the apparatus with its four arms (Fig. 610.) be prevented from rotating, and let it be shown that the escape or discharge of electricity causes motion in the air in the opposite direction, i.e. moves away the air from each of the points, tangentially to the circle. I> VOLUMKTBIC BLBCTRICITT. 91 the machine is worked, be received on the interior of a glass tumbler, by which the surface of the glass will become charged with electric city. If a number of pith balls be id upon a metallic plate communicat- ing with the ground, and the tumbler be placed with its mouth upon the plate, including the balls within it, the balls will begin immedi- ately leaping violently from the metal and striking the glass, and this action will continue till all the electricity with which the glass was charged has been carried away. This is explained on the same principle as the former experiments. The balls are attracted by the electricity of the glass, and when electrified by contact, are repelled. They give up their electricity to the metallic plate, from which it passes to^the ground ; and this pro- cess continues until no electricity remains on the glass of suiiicient strength to attract the balls." Lardner's Natural Philosophy. (1796.) Curious experiments on electrified water. — " Let a small metallic bucket B., Fig. 619, be sus- pended from the prime conductor of a machine, and let it have a capillary tube C. D., of the siphon form, immersed in it ; or let it have a capillary tube inserted in the bottom ; the bore of the tube being so small that water cannot escape from it by its own pressure. When the machine is put in operation, the particles of water, becom- ing electrified, will repel each other, and immediately an abundant stream will issue from the tube; and as the particles of watar after leaving the tube still exercise a reciprocal repulsion, the stream will diverge in the form of a brush. If a sponge, saturated with water, be suspended from the prime conductor of the machine, the water, when the machine is first worked, will drop slowly from it ; but when the conductor becomes strongly electrified, it will descend abundantly, and in the dark will exhibit the appearance of a shower of luminous rain." (Note.) In connection with this the reader may be reminded of the occasionally luminous appearance of (seawater) the surface of the ocean in the very I'^autiful phenomenon known as the phosphores- cence of the sea.* * This " phenomenon is usually attributed, incorrectly we opine, to the presence of some form of animal or vegetable life, which is supposed, to be distributed on the surface in vast numbers of minute individuals. 92 THI OOMIT'b LtTMINOtrS TRAIN. To apply these examples to the case of the comet. If we consider the sun as the body charged with electricity, and the comet as the insulated conductor, it becomes readily understood that the inductive power of the sun will cause the electricity of the comet to accumulate on the side opposite to itself. We have already called atten- tion to the fact that the physical condition of the matter at the comet's surface must be highly favourable to the ■development of free electricity or, to speak more strictly, to the elimination of force in the form of free volumetric electricity. The sun's action on the comet, will conse- Sat each of the particles composing the sorface of a liquid is aflbcted bj an alternate vertical motion. This motion, however, not being simul* taneous but successive, an effect will be produced on the surface which mil be attended with the form of a wave, and such wave will be progressive. The alternate vertical motion by which the particle* oi^the 'iquid are affected will however sometimes take place under such conditions as to produce not a progressive but a stationary undulation. This would be the case if all the particles composing the surface were simultaneously moved upwards and downward* in the saa7e direction, their spaces varying in magnitude according to their distance from a fixed point. To explain this, let us suppose the particles of the surface of a liquid between the point «. «. Fig. 234, (PI. 1) to be simultaneously moved in vertical lines upwards, the centre particle c. being raised through a greater space than the particles contiguous to it on either side. The heights to which the M UNDULATION OF LIQUIDS. Other Bucceeding particles are raised will be continually diminishing, so tlint at the end of a second the particles of liquid which, when at rest, turini'd the Burlacea. e. will form the curved surface a. b. c. d. e. In like manner, suppose the particles of the surface e. i. to be depressed in vertical lines corresponding exactly with those through which the particles a, e. were elevated. Then the particles which originally fomieil the surface e. i. would form the curved surface e.f. g. h. i," and they would become the depression of a wave. Thus the elevation of the wave would be a, b. c. d. e., and its depression t.f.g. A. i. . • X Having attained this form, the particles of the surface a. b. c. d. e. would fall in vertical lines to their primitive level, and having attained that point, would descend below it ; while the particles e.f. g. A. t. would rise to their primitive level, and, having attained that position, would continue to rise above it. In fine, the particles which originally formed the surface of the undulation a. b. c. d. e.f. g. A. i, would ultimately form thesurfacea.' b.' c' d.' «.'/.' g: A.' t.' represented by the dotted line. Having attained this form, the particles would again re> turn to their primitive level, and would pass beyond it, and so on alternately. In this case therefore, there would be an undulation, but not a progressive one. The nodal points would be a. e. i. n. r. and these points, during the undulation, would not be moved ; they would neither sink nor rise, the undulatory motion affecting only those between them. This phenomenon of a stationary undulation pro- duced on the surface of a liquid may easily be explained, by two systems of progressive undulation meeting each other under certain conditions, and producing at the points we have here called nodal points the phenomenon of interference, which we shall presently ex- plain." ^-^^f .<':■• ,•• ■■' .^ - ■_ 1 802. " D^th to which the effect of waves extend.— Whea a system of waves is produced upon the surface of a liquid by any disturbing force a question arises to what depth in the liquid this disturbance in the equilibrium extends. It is possible to suppose a stratum of the liquid at any supposed depth below which the vertical derangement would not be continued. Such a stratum would operate as the bottom of the agitat'id part of the fluid . The Messrs. Webber, to whose experimental inquiries in this de- partment of physics, science is much indebted, have ascertained that From Lardmtr'i Natural Philowphy. Pliti I. The Form and Rtfteetion <^ If ar««. REFLECTION OF WAVES. 95 ifhe equilibrium of the liquid is not disturbed to a greater depth than ■about thremarkaUe elegance by the Meseere. Webberalready refer- red to. These phenomena are represented in Fig. 240, PL3, where a. and b. are the two foci. The strongly marked circles indicate t^e elevation, of the waves formed around each focus, and Uie more lightly traced, circles indicate their depression . The points wLere the strongly mark*- ed circles intersect the more &intly mariced circles, being point? where an elevation coincides with a depression, are coaaeqnently- points of interference, according to what has > een just explained. The series of these points form lines of interference, which are marked in the diagram by the dotted lines, and which, as will be seen, have the- forms of ellipses and parabolas round the same foci." 812. "Jn/fection o/* toovM.— -If a series of waves encounter a solid surface in which there is an opening through which the waves may be admitted, the series will be continued inside the opening and with' out interruption ; but other series of progressive waves having a circu*^ lar form will be generated, having the edge of the opening as their centres. Let M. N., Fig. 241, PI. 3, represent such a surface, having an opening whose edges are A. and B.. and let C. be a centre from which a series of progressive circular waves is propagated. These waves. ■I I 1 4 1 Fy-om Lardner't Natwral Philotophy. Plati III. Fig 241 Fig. 240 Interjerenee and Inflttion i\f Wnvn. UNDULATION OF BLASTIO FLUIDS. ■' Wf- entering at the opening A.B., will continue their oouri,e uninterrupted forming the circular arcs D. E. But around A, and B. as centres, sys- tems of progreeflive circular waves will be formed which will unite with the waves D.E., completing them by circular arosD.jP. and E.F, meeting the obstructive surface on the outside ; but these circular waves will also be formed throughout the remainder of tlieir extent, as indicated in the figure, on both sides of the obstructing surfitce, and intersecting the original system of waves propagated from the centre C. They will also form with these, series of points of interference according to the principles already ezpliuned. The effects here described as produced by the edges of an opening through which a series of waves is transmitted is called inflection, and it will appear hereafter that they form an important feature in several branches of physics whose theory is based upon the prinoifdesofun' dulation." Quotation from Lardner's Natural Philosophy, continued :— Undulation of Elattic Fluids. " If any portion of the atmosphere, or any other elastic fluid diffused through space, be suddenly compressed and immediately relieved ftom the compressing force it will expand in virtue of its elasticity, andr like all other 8imiK^r examples already given, will, after its expansion^ exceed its former volume to a certain limited extent, after which it will again contract, and thus oscillate alternately on the one side and on the other of its position of repose. 814. " Undulations of a sphere of air. — ^We may consider this effect- to be produced upon a small sphere of air having any proposed radius, as, for example, an inch . Let us suppose that it is suddenly compressed so as to form a sphere of half an inch in radius, and being relieved . ^. to .^. would be to push the remote extremity T. through a space to the right corresponding with and equal toS. A. -••■{ > ' < 11 1 S AAA' BB'lT But such an effect does not take place, first, because air is highly «la8tic, and has a tendency to yield to the force excited by the solid surface upon it while it moves from S.to A.; and secondly, because to transmit any effect from ^. to a remote point, such as T., would require a much greater interval of time than that which elapses during the movement of the surface from S. to A. The effect, there- fore, of the compression, in the interval of time whicii elapses during the motion from S.U> A.,iB to displace the particles of air which lie at a certain definite distance to the right of A. Let this distance for AERIAL UNDULATIONS. 99 example be A. B. All the particles, therefore, of air which lie in succession from^. to B. will be effected more or less by the com- pression, and will consequently be brought into closer contiguity with each other ; but they will not be equally compressed, because to enable the series of particles of air lying between A. and B. to assume a uniform density requires a longer time than elapsee during the motion of the solid surface from S. \jo A. At the instant, therefore, of the arrival of the compressing surface at A. the line of particles between A. and B. will be at different distances from each other ; and it is proved by mathematical principles, that the point where they are most closely compressed is the middle point m. between A. and B. and therefore, departing from the middle point m. in either direc- tion, they are less and less compressed. The condition, therefore, of the air between A. and B. is as follows. Its density gradually in- creases from A. to m. and gradually decreases from m. to B. Now, it is also proved that the effect of the elastic force of the air is such that, at the next moment of time after the arrival of the compressing surface at A the state of varying compression which has just been ■described as prevailing between A. and B. will prevail between an- other point in advance of A. such as A . and a point B . equally in advance of fi., and the point of the greatest compression will, in like manner, have advanced to m'. at the same distance to the right of m. In short, the conditions of the air between A . and B . will be in all respects similar to its condition the previous moment between A. and B., and in like manner, in the next moment, the same condition will prevail between the particles A" . and li', to the right of A', and B. Now, it must be observed that as this state of varying density prevails from left to right, the air behind it, in which it formerly prevailed, resumes its primitive condition. In a word, the state of varying density which has been described as prevailing between A. and B- at the moment the compressing surface arrived at.^. will in the succeed- ing moments, advance from left to right towards T., and will so advance at a uniform rate ; the distance between the points A. B. A' . B , and A'. B',, &c., always remaining the same." 816. " Aerial undulations. — This interval between the points A. and B. is called a wave or undulation, from its analogy, not only in form but in its progressive motion, to the waves formed on the surface of liquids, already described : the difference being that in the one case the centre of the wave is the point of greatest elevation of the 100 AIRIAL UNDULATIONS. surface of the liquid, and in the other case it is the point of greatest condensation or compression of the particles of the air. The distance between A. and B. or between A', and B'. or between A", and B",, which always remains the same as the wave progresses, is called the length of the wave. ,.• « ■ In what precedes we have supposed the compressing surface to advance fVom S.to A. and to produce a compression of the air in ad- vance of it. Let us now suppose this surface to be at .4., the air conti- guous to it having its natural density. If the w&ve proceed eontrariwiae from A. to S, the air which was contiguous to it at 4. will rush after it in virtue of its elasticity, so that the air to the right of A. will be disturbed and rendered less dense than previously. An effect will be produced, in fine, precisely contrary to that which was produced when the wave advanced from S.to A. i the consequence of which will be that a change will be made upon the air between A. and B. exactly the reverse of that which was previously made, that is to say, the middle point m. will be that at whicl . the rarefaction will be greatest, and the density will increase gradually, proceeding from the point m. in either direction towards the points A. and B. The same observations as to the pro- gressive motion will be applicable as before, only that the progression m. instead of being the point of greatest condensation, will be the point of least density." 817. " Wave3 condensed and rarejied. — The space A, B. is also in this case denominated a wave or undulation. But these two species of waves are distinguished one from the other by being denomina. ted, the former a condensed, and the latter a rarefied wave. Now, let it be supposed that the compressing surface moves alternately backwards and forwards between S. and A. making the excursions in equal times. The two series of rvaves, as already defined, will be produced in succession. While the condensed wave moves from S. towards T. the rarefied wave immediately follows it, xnd in the same manner this rarefied wave will be followed by another condensed wave, produced by the next oscillation, and so on. The analogy of these phenomena to the progressive undulation on the surfiice of a liquid, as already described, is obvious and striking. What has been here described with reference to a single line of particles extending from the centre of the distance ^. in a particular direction, is equally applicable to every line diverging in every con- AERIAL UNDULATIONS. 101 ■ceivable direction around such centre, and hence it follovrs that the succesaionof condensed and raretled waves will be propagated round the centre, each wave forming a spherical surface, which is continually progressive and uniformly enlarges, the wave moving from the common centre with a uniform motion." 818. " Velocity and force of Aerial leavu. — The velocity with which such undulatious are propagated through the atmospliere depends on, and varies with, the elasticity of the fluid. The degree of compreHsion of the wave which corresponds to the height of a wave in the case of liquids, depends on tlie energy of the disturbing force. All the effects which have been described in the case of waves formed upon the surface of a liquid are reproduced, under analogous conditions, in the case of undulations propagated through the atmosphere." 819. " Their interference. — Thus, if two series of waves coincide as to their points of greatest and least condensation, a series will be formed whose greatest condensation and rarefaction is determined by the sum of points, as prevailing in the separate undulations;* and if the two series are so arranged that the points of greatest condensation of the one coincide with the greatest rarefaction of the other, and, vice verad, the series will have condensations and rarefactions deter- mined by the ditterence of each of the separate series ; and, in fine, if in this latter case the condensations and rarefactions be equal, the un- dulations will mutually efface each other, and the phenomena of in- terference, already described as to liquids, will be reproduced. As the undulations produced in the air are spread over spherical surfaces having the centre of disturbance as a common centre, the magnitude of these surfaces will be in the ratio of the squares of the radii, or what is the same, of the squares of their distances from the point of central disturbance ; and as the intensity of the wave is diminished * See the note at page 95. Assuming that the soundness of the objection stated in that note has to be allowed, it is not perhaps quite so obvious that it will also apply to the case above. We opine, however, that (assum- ing the possibility of an aerial wave such as described) the two cases ate, in respect to this particular, strictly analogous, and that, consequently, the same objection does apply ; namely, that the coincidence of two undulations (or waves) in the elastic fluid will not increase the condensation and rare- faction as stated above but will increase the amplitude and wave length of the undulation. • . . 102 AERIAL UNDULATIONS. in proportion to tlic space over which it in diifufled, it follows that the ettectB or energy of these waves will diminish as the^squares of their distances from the centre of propagation increase." It appears to us that certain of the propositions relat- ing to interference in the (liquid) wave theory, as stated in the preceding quotation, are not sufficiently supported by experimental demonstration and are by no meana satisfactorily established. In the four cases, stated art. 809, of two systems of waves encountering each other, it seems most probable that, whether the elevations and depressions of the one coincide with those of the other or whether they do not coincide, the two waves will de- stroy or neutralize each other ; and, moreover, it seems probable that such neutralization would take place immediately in the case where the elevation of the one coincided with the elevation of the other, • (but this is directly the contrary to Dr. Lardner's statement in the preceding quotation), whereas if the elevation of the one coincided with the depression of the other, the one would probably pass over and under the other, and both would continue to undulate in the opposite directions for a limited distance and only gradually destroy each other by an interference which might be called frictional. The propositions would, as it seems to us, apply more cor- rectly to two systems of waves travelling (or propagated) in the same direction, the undulations of the one having a gi'eater velocity than, and overtaking, the other. (It is on the assumption of an actual interference of the kind supposed that the objection to the particular case contain- * If, however, the elevation and depression of the encountering waves be considerable, both waves would be partially reflected, and this reflection would be more complete the greater the velocity of the encountering "*■:. *; waves. AERIAL UNDULATI0N8. 103 ed in the note at p. 16 is made, and we are not to be under- stood thereby as affirming or admitting the soundness of any part of the general theory to which these propositions belong.) But the same propositions are applied, Art. 819, to interference of encountering undulations in elastic fluids ; and it is, as appears, at once assumed, on the ground of analogy only, that these propositions are to be accepted as (fact) postulates or axioms. But the objec- tion taken to them in their application to the liquid wave also applies, and even more obviously, to tlie encounter- ing undulations of the elastic fluid. If two equal undu- lations encounter from opposite directions it seemn almost obvious either that they most destroy (neutralize) each other, or that both of them must be reflected ; but Nos. I. and III. of the propositions, applied to elastic fluids in Art. 819, teach that in such case, the effect (in the compression and rarefaction of the resulting undula- tion) is the sum of the two undulations ; without defin- ing, however, in vvhicii direction the resulting undula- tion or wave is to proceed. In the case of proposition II., where the resulting wave or undulation is stated to be the difference of the two, the doctrine does not appear so incredible — although, in this case, the result which any- one acquainted with the laws and phenomena belonging to mechanical science would probably expect to find, would be a velocity in the resulting wave or undulation equal to the difference in the velocities of the encountering unequal undulations. ,^ .< . ; ., i However, the entire theory in its application to elastic fluids, as set forth, is quite at variance with the known facts and established laws of mechanical science. What should be our answer if cfiUed upon to admit that a pound 101 ABBtAL IT5DCLATI0NI. of water in descending one foot could develope or elimin- ate mechanical power capable of raising a ton weight of water not only to a height of one foot but to a height of an unlimited or indefinite number of miles f Yet such assumption is substantially contained in the doctrine here set forth. Referring to tlie illustration, Fig. 342, " let S. A. represent the space through which the disturbing force acts, and let us imagine this air suddenly pressed from S. to A. by some solid surface moving against it, and let us suppose that this motion from S. to A. is made in a second." Herein we have clearly stated the definite exciting or developing cause of a definite quantity of mechanical force or power, because a definite amount of compression in a definite time of a definite quantity of Air (or other elastic fluid) represents a definite amount of mechanical power just as certainly as the descent ot u ^'^' ' "^ : ^ • ■ We may here take the opportunity, also, to remarh the hy- pothetical definitions contained in the several terms tised by teachers to denote the imjmlses in connection tvith the partial explanations tvhich frequently accompany their use, e.g., tin- 114 AERIAL UNDVLATIONH. (lulations, waves, vibrations, wave-lengths of tJ^e vibrations, or of the oscillations, longitudinal oscillating motions of the particles of ether; transverse oscillating motions of the particles of ether, eing communicated to the pump- plate, let the receiver be exhausted in the usual way. When the air has been withdrawn, let the bell be made to ring by means of the sliding rod. No sound will be heard, although the percussion of the tongue upon the bell, and the vibration of the bell itself are visible. ■''ation ; and those vibrations impart vibrations to the external air which are transmitted to the ear. If in the preceding experiment a cushion had not been interposed' between the alarum and the pump-plate, the sound of the bell would have been audible, notwithstanding the absence of air from the receiver. " The vibration in this case would have been propagated, first fronv the bell to the pump- plate and the bodies in contact with it, and thence to the external air." 822. " A continuous body oj air not necessary. — Persons shut up in a close room arc sensible of sounds produced at a distance outside such room ; and they may be equally sensible of these, evCi* though the windows and doors should be absolutely air-tight. In such case the undulations of the external air produce sympathetic vibra> tion on the windows, doors or walls by which the hearers are en- closed, and then produce corresponding vibrations in the air within the room, by which the organs of hearing are immediately affected."' 823. " Propagation of sound proffressive. — Let a series of observers » A. B. C. &c., be placed in aline, at distances of about 1000 feet asun- der, and let a pistil be discharged at P. about 1000 feet from the first observer. Pi- — f- —t- e — i~ X — «- —4 This observer will see the flash of the pistol about one second be- fore he hears the report. The observer B. will hear the report one second after it has been heard by A. and about two seconds after he sees the flash. In the same manner, the third observer at C will hear the re- port one second after it has been heard by the observer at B. and two seconds after it has been heard by the observer at A. and three seconds afler he perceives the flash. In the same way, the fourth observer at JD. will hear the report one second later than it was heard by the third PROPERTIES OF SOUND. 117 observer at C. and three seconds later than it was lieard by the o\ • «erver at A, and four seconds after he perceives the flash.. Now it must be observed, that at the moment the report is heard by the second observer at B. it has ..eased to be audible to the first ob- server at A., and when it is heard by tlie third observer at C. it has ^jeased to be heard by the second observer t,i B ., and so forth. It follows, therefore, from this, that sound passes through the air, not instantaneously, but progressively, and at a uniform rate." 824. " Breadth of sonorous waves.— -As the sensation of sound is produced by the wave of air impinging on the membrane of the ear- drum exactly as the momentum of a wave of the sea would strike the «hore, it follows that the interval between the production of sound and its sensation is the time which such a wave would take to pass through the air from the sounding body to the ear ; and since these waves are propagated through the air in regular succession, one following -another without overlaying each other, as in the case of waves i pon a liquid, the breadth of a wave may always be determined if we take the number of vibrations which the sounding body makes in a second, and the velocity with which the sound passes through the air. If, for ex. ample, it be known that in a second a musical string makes 500 vibrations, and that the sound of this string takes a second to reach the ear of a person at a distance of 1000 feet, there are 500 waves in the distance of 1000 feet, and consequently each wave measures two feet. The velocity of the sound, therefore, and the rate of vibration, are Always sufficient data by which the length of the sonorous wave can be computed." , 826. " Distinction between musical sounds and ordinary sounds. — It has not been ascertained, with any clearness or certainty, by what physical distinctions vibrations which produce common sounds or noises are distinguisheil from such as produce musical sounds. It is nevertheless certain, that all vibrations, in proportion as they are regular, uniform and equal, produce sounds proportionably more agreeable and musical. Sounds are distinguished from each other by their pitch of tone, in virtue of which they are high or low by their intensity, of which they are loud or soft ; and by a property expressed in French by the word timbre which we shall here adopt in the absence of any English equivalent." 118 PROPERTIES OF SOUND. 82<5. " Pitch of a sound. — The pitch or tone of a sound is grave or acute. In tlie former case it is low, and in the latter high, in *he musical scale. It will be shown hereafter that the physical condition which determines this property of sound is the rate of vibration of the sounding body. The more rapid the vibrations are, the more acut& v'iil be the sound. A bass note is produced by vibrations much less rapid than a note in the treble. But it will also be shown that the- length of the sonorous wave depends on the rate of vibration of the- body which produces it: the slower the rate of vibration, the longer will be the wave, and the more grave the tone. All the viliration» which are performed at the same rate produce waves of equal length and sounds of the same pitch." 827. " Intensity or Loudness.— Tl\e intensity of a sound or its degree of loudness, depends on the force with which the vibrations of the sounding body are made, and consequently upon the degree of condensation produced at the middle of the sonorous waves. Waves of equal length, but having different degrees of condensation at their centre, will produce notes of the same pitch, but of different degrees of loudness, in proportion to such degrees of condensation." 828. " Timbre of a sound. — The timbre of a sound is not easily- explained ; and still less easily can the phyjical conditions on which it depends be ascertained. If we hear the same musical note produced with the same degree of loudness in an adjacent room successively upon a tlute, a clarionet, and a hautboy, we shall, without the least> hesitation, distinguish the one instrument from the other. Now, this- distincC:on is made by observing some peculiarity in the notes prO' duced, yet the notes shall be the same, and be produced with equal loudness. This property by which the one sound is distinguished from the other, is called the timbre." 829. •* All aoittt'^1 propagated with the same velocity.~-AU sounds, whatever be their pitch, intensity, or timbre, are propagated through the same medium with the same velocity. That this is the case, is manifest from the absence of all confusion in the effectrfof music, at whatever distance it may be heard. If the different notes simultane- ously produced by the various instruments of an orchestra movecB with different velocity through the air, they would be heard by a. distant audit'^r at different moments, the consequence of which would be, that a musical performance would, to the auditors, save those in immediate proximity with the performers, produce the most intolera- PROPERTIES OF SOUND. 119 ble confusion and cacophony ; for, different notes produced simultane- ously, and which, when heard together form harmony, would at a distance be heard in succession, and sounds produced in succession would be heard as if produced together, according to the different velocities with which each note would pass through the air." 030. " Experiments on the velocity of sound. — The velocity of sound varies with the elasticity of the medium by which it is propagated . Its velocity, therefore, through the air, will vary, more or less, with the barometer and thermometer. . ', - The experimental methods which have been adopted to ascertain the velocity of sound are similar in principle to those which have been briefly noticed by way of illustration. -The mo.-^ extensive and accurate system of experiments which have been made with this object were those made at Paris by the Board of Longitude in Uie year 1822. The sounding bodies used on this occasion were pieces of artillery charged with from two to three pounds of powder, which were placed at Villejuif and Montlh6ry. The experiments were made at midnight, in order that the flash might be more easily and accura- tely noticed. They were conducted by MM. Prony, Arago, Mathieu, Humboldt, Gay Lussac, and Bouvard. Tht result of the experiment was that, when the barometer was at 29.8 inches, and the thermome- ter at 61°, the velocity of sound was 1118.39 feet per second. By calculation it is ascertained, that at the temperature of 50°, the velocity would be 1106.58 feet per second; and aVif, the velocity would be 1086.37 feet per second. Thus it appears that between 50° and 61°, the velocity of sound increases about 1.07 feet per second for every degree which the ther- mometer rises, and between 50° and 32°, it increases at the mean rate of 1.12 feet per second for each degree in the rise of the thermometer. 831 . " Method of estimating the distance of a sounding body by velocity of sound. — The velocity of sound being known, the distance of a sounding body can always be computed by comparing the moment the sound is produced with the moment at which it is heard. The production of sound is in many cases attended with the evolution of light, as, for example, in fire-arms and explosions generally, ami iti the case of atmospheric electricity. In these cases, by noting tlie interval between the flash and the report, and multiplying the nmnber of seconds in each interval by the number of feet per second in the velocity of sound, the distance can be ascertained with great precision. 120 PROPERTIES OP SOUND. Thus, if a flash of lightning be seen ten seconds before the thunder, -which attends it, is heard, ami the atmosphere be in such condition that the velocity of sound is 1120 feet per second, it is evident that the distance of the cloud in which the electricity is evolved must be 11,200 feet. Among the iiumerous discoveries bequeathed to the world by New- ton, was a calculation, by theory, of the velocity with which sound was propagated through the air. This calculation, based upon the elasticity and temperature of the air, gave as a result about one sixth less than that which resulted from experiments. This discrepancy remained without satisfactory explanation until it was solved by Laplace, who showed that it arose from the fact that Newton had neglected to take into account, in his computation, the effect of the heat developed and absorbed by the alternate compression and rare- faction of the air produced in the sonorous undulations. Laplace taking account of these, gave a formula for the velocity of sound which corresponds in its results equally with experiment." 832. " All gases and vapours conduct sound. Experimental illus- trations. As all elastic fluids are, in common with air, susceptible ot undulation, they are equally capable of transmitting sound. This may be rendered experimentally evident by the following means. Let "the alarum be placed under the receiver of an air pump, an already descibed, and let the receiver be exhausted. If, instead ot introduc- ing atmospheric air into the receiver we introduce any other elastic fluid, the sound of the alarum will become gradually audible, accord- ing to the quantity of such fluid which is introduced under the recei- ver. If a drop of any liquid which is easily evaporated be introduced, the atmosphere of vapour, which is thus produced, will also render the alarum audible." 833. " Thiintensity of a sound increases with thedensily of the pro- pagating medium. — The same sounding body will produce a louder or lower sound, according as the density of the air which surrounds it is increased or diminished. In the experiment already explained, in which the alarum was placed under an exhausted receiver, the sound increased in loudness as more and more air was admitted into the receiver. If the alarum had been placed under a condenser, and high- ly compressed air collected round it, the sound would have been still further increased. When persons descend to any considerable depth in a diving-bell, the atmosphere around them is compressed by the PROPERTIES OF SOUND. 121 weight cf the column of water above them. In such circumstances, a whisper is almost as loud as the common voice in the open air, and when one speaks with the ordinary force, it produces an effect so loud as to be painful.* On the summit of lofty mountains, where the barometric column falls to one half its usual elevation, and where, therefore, the air is highly rarefied, sounds are greatly diminished in intensity. Persons who ascend in balloons find it necessary to speak with much greater exertion, and as would be said louder, in order to render themselves audible. When Saussure ascended Mont Blanc, he found that the report of a pistol was not louder than a common cracker."t 837. " Eifperimenial illustration of interference of sound, — This phenomena of interference may be produced in a striking manner by means of the common tuning-fork, used to regulate the pitch of musi- cal instruments. Let A, and B., Fig. 243, be two cylindrical glass vessels, held at right angles to each other, and let the tuning- fork, after it has been put in vibration, be held in the middle of the angle formed by their mouths. Although, under such cir- cumstances, the vibration of the tuning-fork will be imparted to the columns of aiir included within the two cylin- ders, no sound will be heard ; but if either of the cylinders be removed the sound will be distinctly audible in the other. In this case the silence produced by the combined sounds iu the consequence of inter- * But, is this the effect as nsually experienced ? We have a recollection under such circumstances, of a sensation of oppression in the ears, and as of a continued peculiar noise, accompanied with a considerable difficulty in hearing any one speak. t These instances are given as evidences in support of the proposition that the transmitting or propagating capability of the elastic fluid increases or decreases according to the increased or decreased density of the fluid. But they do not in themselves furnish any conclusive evidence, becaase the effects noticed may be, with equal probability, attributed to another cause. The necessity for greater exertion in the balloon may arise from a difficulty in speaking instead of a difficulty in hearing ; and again, if the noise, in quantity of sound, be de|>endent on the concussion, the rarefaction of the air would diminish the violence of the concussion [occasioned by the explosion] in firing the pistol, and consequently less noise or quantity of sound would be produced. 122 PROPEBTIES OF SOUND. ference. Another example of this phenomenon may be produced by the tuning- fork itself. If this instrument, after being put into vibra- tion, be held at a great distance from the ear, and slowly turned round its axis, a position of the prongs will be found at which the sound will become inaudible. This position will correspond to the points of interference of the two systems of undulation propagated from the two prongs." 838. "Examples of sounds propagated by solids.— SoVida which possess elasticity have likewise the power of propagating sound. If the end of a beam composed of any solid possessing elasticity be lightly scratched or rubbed, the sound will be distinct to vholly spiritual. Nevertheless, there is abundant evidence that each of these forces can and does exert a potent influence on matter, and a distinction in the general character of the effects on matter caused respectively by each of them may be made : — Light acts molecularly (chemically) disturbing the internal molecular arrangement and in some cases causing combination or decomposition of the elements of the compounded matter. Sound acts volumetrically (mechafiically) occasioning alteration in the arrangement, or dynamical disturbance in the relative positions, of ihe aggregated particles of which the matter consists. The objection which we stated to the undulatory theo- ry of light, viz., that it has not been shown or explained how a number of undulations propagated through a material fluid (the ether) in various directions can cross each other at angles of all degrees of obliquity and yet not destroy, interfere with or modify each other, applies also to the aereal waves or vibratory pulses which are supposed to propagate the effect called sound. We are decidedly of opinion that this objection alone in its application to the aereal wave theory of sound is quite insurmountable and fatal. Other fadts opposed to the theory and irreconcilable with it, have been, in our quotations from the record, abundantly put before the reader : for example, (1) the conduction or transmission of sound through water and through metallic and other NATURK or SOUND. 125 solid bodies with considerably greater velocity than through air. In the undulatory theory' of light the hypothetical ether is supposed to occupy the interstices between the constituent particles of metals and other solids : but in the kindred theory of the aereal sound undulations, not even hypothesis can venture to suppose the interstices between the particles of metals and other solids, occupied by air. (2) The much greater velocity with which sound is transmitted by the medium of these solids. (3) Ghladni's experiment of two persons con- versing by means of a stick held between the teeth, having their ears stopped. (4) The familiar fact that sound is transmitted through air in one direction whilst the air itself is in rapid motion in the opposite direction. (5) The fact that a feeble and a very loud sound are transmitted with equal velocities. We are not disputing or questioning the established facts of acoustics. That the mode of the communication in which the acoustic force is transmitted from the place where the active force is disengaged to the recipient, is such as may be termed an undulation or vibratory pulse, and tha^ the note or quality of the sound is dependent upon the greater Oi lesser rapidity, and upon the regu- larity or iiTegularity of the vibrations, is, we opine, established as a general fact belonging to the subject. Many of the subordinate regulations or laws, under which the manifestations of this force upon matter operate, have been successfully investigated. It is not, however, the purpose of this work to enter at length into the particular facts and phenomena belonging to such a department of science as acoustics and optics further than is necessary to support and establish the 186 NATDRI or BOUND. Bv. i '.■ opinions we have advanced on the fundamental doctrines pertaining to the subjects of sound and light. The record of most of the interesting and important investi- gations which have been made in this department is con- tained in the comprehensive and very useful treatise of Dr. Lardner from which we have so largely quoted. Students of scien^'e wishing to become acquainted with the most recent physical observations and discoveries relating to acoustics illuF.trated by refined exposition and experiment may avail themselves of the instruction afforded by Prof. Tyndall's Eight Lectures on Sound. MANIFESTATIONS OF FORCE ON MATTER, HAOMETIO AND THERMAL EFFEOTH OF ELEOTRIOITT, Fovine's Manual of Chtmiatry. Part I. PhysicH, page 72. | '* Not long before two very remarkable facts — *■ had been discovered. Oersted, in Copen- hagen, showed that a current of electricity, however produced, exercises a singular and perfectly definite action on a magnetic needle ; and Seebeck, in Berlin, found that an electric current may be generated by the Fig. 52. unequal effects of heat on different metals in contact. If a wire conveying an electrical current be brought near a magnetic needle, the latter will immediately alter its position and assume a new one, as nearly perp?ndicular to the wire as the mode of suspension and the magnetism of the earth will permit When the wire, for example, is placed directly over the needle, while the current it carries travels from north to south, the needle is deflected from its ordinary direc- tion and the north pole driven to the eastward. When the current is reversed, the same pole deviates to an equal amount towards the west. Placing the wire below the needle instead of above produces the same effect as reversing the current. When the needle is subjected to the action of two currents in opposite directions, the one above and the other below, they will obviously concur in their effects. The same thing happens when the wire carrying the current is bent upon itself, nnd the needle Fig. 53. placed between the two portions ; and since every time the bending is repeated a fresh portion of the current is made to act in the same man- ner upon the needle, it is easy to see how a current, too feeble to pro- duce any effect when a single straight wire is employed, may I* made by this contrivance to exhibit a powerful action on the magnet. It is on this principle that instruments called galvanometers, galvanoscopes. 128 MAGNITISM AND KLEOTRIOITT. or multipliers are constructed t thej Aerve, not only to indicate the existence of electrical currenls, but to show by the effect upon the needle the direction in which they are moving. By using a very_ long coil of wire, and two needles, immovably connected, and hung by a fine filament of silk, almost any degree of sensibility may be com- municated to the apparatus.* Fig. 69. When two pieces ofdifTerent metals connected together at each eml, have one of their points more heated than the other, an electric current is immediately set up. Of all the metals tried, bismuth and antimony form the most powerful combina- tion. A single pair of bars, having one of their junctions heated in the manner shown, can develope a current strong enough to Fig. 64 (a). * The cummon galvanoscope, consisting of a coil of wire having a com- pass-needle suspended on a point within it, is greatly improved by the addition of a second needle, as already in part described, and by a better mode of suspension, a long fibre of silk being used for the purpose. The two needles are of equal size, and magnetized as nearly as possible to the same extent ; they are then immovably fixed together, parallel, and with their poles opposed and hung with the lower needle in the coil and the upper one above it. The advantage gained is two-fold : the system is attatie, un- affected, or nearly so, by the magnetism of the earth ; and the needles being both acted upon in the same manner by the current, are urged with much greater force than one alone would be, all the actions of every part of the coil being strictly concurrent. A divided circle is placed below the upper MACINETISM AND BLKOTRIOITY. 129 deflect a oompans-needle placed within, and, by arranging a number in a series and heating their alternate ends, the intensity of the our- Fig. 64. rent may be very much increased. Such an arrangement is called a thermo-electric pile. M. Melloni constructed a very small thermo- electric pile of this kind, containing fifly-five slender bars of bismuth and antimony, luid side by side and soldered together at their alter- nate ends. He connected this pile with an exceedingly delicate multiplier, and found himself in the possession of an instrument for measuring small variations of temperature far surpassing in delicacy the air-thermometer in its most sensitive form, and having great advantages in other respects over that instrument when employed for the purposes to which he devoted it." ( See Fig. 64). By means of this apparatus, the close analogy between radiant heat and light was made apparent. The example here given illustrates the conversion of heat (caloric force) into molecular-electricity (voltaic electric force). Examples of the connection between Volumetric (fric- tional), and Molecular (voltaic) Electricity are . . .The production of Magnetism, .of Chemical decomposition. . of Light., and of Heat,(e. ^. in the heating and fusion of a conducting wire) .... effects which result from the action of both (i.e., of either one of) those forces, or forms of force, on compound matter. And the relation of ' motion ' and ' mechanical-effect ' to each of those forces is shown in the production of volumetric electricity needle, by which the regular motion can be measured ; and the whole is enclosed in glass, to shield the needles from the agitation of the air. The whole is shown in Fig. 69. 1 li ; 130 MAGNBTI8M AND ELICTBICITY. uy friction in the plate or cylinder electrical machine ; and in the production of molecular electricity by the rotatic^ of an armature (a piece of iron) in front of the poles of a magnet. The production of volumetric electricity by a jet of steam also shows the connection of that force with me- chanical-efiect, and also with heat (because the mechanical effect of the steam results from the addition of caloric force to the water.) And, again, in the development of the same kmd of electricity (volumetric) by or in certain animals (fishes) — e. ^., the Gymnotus, electricity is seen to be closely connected with nervous power, (i. e., with mechanical-effect) . . .the electric shock is given at the will of the animal, and great exhau3tii/n follows the repeated exertion of the power. The proposition that compound matter is compounded of force together with matter, and that t^ o distinctive characteristics of the compound substance are dependent upon the definite proportional quantity of force which enters into its composition and constitutes a part of it, may be demonstrated by the facts belonging to chemical and physical science. i; ■ 1 ! . Lardner's Natural Philosophy. (1799) •' A Ourfent of EleetrieHy passing over a Conductor raises its Temperature. — ^If a current of electricity pass over a conductor as would happen when the conductor of an electrical machine is con- nected by a metallic rod with the earth, no change in the thermal con- dition of the conductor will be observed so long as its transverse sec- tion is BO considerable as to leave sufficient space for the free passage of the fluid. But if its thickness be diminished, or the quantity of fluid passing over it be augmented, or, in general, if the ratio of the fluid to the magnitude of the space afibrded to it be increased, the conductor will be found to undergo an elevation of temperature, which will be MAGNETISM AND XLEOTRIOITT. 131 a. greater the greater thequantityof the electricity and the less the space supplied for its passage." (1800.) " Experimental Verification, Wire heated, fused, and burned. — If a piece of wire of several inches in length be placed upon the stage of the universal discharger, a feeble charge transmitted through it will sensibly raise its temperature. By increasing the strength of the charge, its temperature may be elevated to higher and higher points of the thermonietric scale ; it may be rendered incan- descent, fused, vaporized, an , in fine, burned. With the powerful machine of the Taylerian Museum at Haarlem, Van Murum fnsed pieces of wire, above 70 feet in length. Wire may be fused in water ; but the length which can be melted in this way is always less than in air, because the liquid robs the metal of its heat more rapidly than air. A narrow ribbon of tinfoil, from 4 to 6 inclies in length, may be volatilized by the discharge of a common battery. The metallic vapor is, in this case, oxidized in the air, and its filaments float like Ihose of a cobweb." (1801.) " Thermal effects are greater as the Conducting Power is less. — These thermal effects are manifested in different degrees in different metals, according to their varying powers. The worse con- ductors of electricity, such as platinum and iro:i, suffer much greater changes of temperature by the sam charge than the best conductors, «uch as gold and copper. The caarge of electricity, which only elevates the temperature of one conductor, will sometimes render another incandescent, and will .olatilizea third *' (1802.) " Ignition of Metals. — If a fine silver wire be extended be- tween the rods of the universal discharger, a strong charge will make it burn with a grMnish f!arii«>. It will pass off in a greyish smoke ; other metals may be similarly ignited, each producing a flame of a peculiar colour. If the experiment* be made in a receiver, the pro- ducts of the combustion being collected, will prov<> to be the metallic oxides. If a gilt thread of silk be extended between the rods of the dis- charger, the electricity will volatilize or bum the gilding, without affecting the silk. The effect is too rapid to allon the time necessary for the heat to affect the silk. A strip of gold or silver leaf placed between the leaves of paper, being extended between the rods of the discharger, will be burnt by a ili MOLECTTLAR ELEOTRIOITT AND MATTER. discharge from ajar Laving two square feet of coating. The metallic oxide will in this case appear on tlie paper as a patch of purple colour in the case of gold, and of grey colour in that of silver. A spark from the prime conductor of the great Haarlem machine burnt a strip of gold leaf twenty inches long by an inch and a half broad." (1806.) " Resinous Powder J5urn«rf.— The electric charge trans- mitted through fine resinous powder, such as that of Colophony, will ignite it. This experiment may be performed either by spreading the powder on the stage of the discharger, or by impregnating a hank of cotton with it ; or, m a still more striking manner, by sprinkling it on the surface of water contained in an eathenware saucer." MOLECULAR (VOLTAIO) ELECTRICITY AND HATTER. Fowne's Chemistry, Page 92.— The second form of apparatus, or crown of cups, is precisely the same in principle, although different in appearance. A number of cups or glasses are arranged in a row or circle, each containing a piece of active and a piece of inactive metal and a portion of exciting liquid; zinc, copper, and dilute sul- phuric acid, for example. The copper of the first cup is connected with the zinc of the second, the copper of the second with the zinc of the third, and so to the end of the series. On establishing a commu- nication between the first and last plates by means of a wire, or other- wise, disciiarge takes place in the form of a bright enduring spark or stream of fire. (Page 206). "When a voltaic current of considerable power is made to traverse various compound liquids, a separation of the elements of these liquids ensue* ; provided that the iiijuid be capable of conducting a current of iv certain degree of energy, its decomfjosi- tion almost directly follows. The elements are disengageil solely at the limiting surface of the MOLECULAR ELEOTRIOITT AND MATTER. 133 liquid ; where, according to the common mode of speech, t1>e current enters and leaves the latter, all the intermediate portions appearing perfectly quiescent. In addition, the elements are not separated indit- ferently and at random at these two surfaces, but, on the contrary, make their appearance with perfect uniformity and constancy at one or ! ' )ther, according to their chemical character, namely — oxygen, chlorine, iodine, acids, etc., at the surface connecteil vith the copper or potitive end of the battery; hydrogen, the metai.->, etc., at the surface in connection with the zinc or negative extremity of the arrangement.* The terminations of the battery itself, usually, but by no means necessarily of metal, are designated poles or electrodes, as by their intervention *^i' liquid to be experimented on is made a part of the circuit. The process of decomposition by the current is called eUctrolyaic, and the liquids, which, when thus treated, yield up their elements, are denominated electrobftes. When a pair of platinum plates are plunged into a glass of water to which a few drops of oil of vitriol have been added, and the plates connected by wires with the extremities of an active battery, oxygen is disengaged at the positive electrode, and hydrogen at the negative, in the proportion of one measure of the former to two of the latter nearly. A solution hjrdrochloric acid mixed with a little Saxon blue (indigo), and treated in the same manner, yields hydrogen on the negative side, and chlorine on the positive, the indigo there becoming bleached. Iodide of potassium dissolved in water is decomposed in a similar manner, and with still greater ease ; the free iodine at the positive side can be recognized by its brown colour, or by the addition of a little gelatinous starch. *Note the evidence here that compounded matter as usually- cognized by us, is comptmnded of force and matter ; and that the aeave force may be transmitfed (communicated) through the'MMnbined (latent) force without either mechani- cal or moiecimlar disturbance of the material elements. This evidence may be compared with that in Optics and Acous- tics, where the communication or transmission of the force through air (or through other fluid or solid) is unattended with displacement of the material particles. ii i 184 MOLEOULAB ELEOTRIOITT AND MATTS.B. Every liq" d is not an electrolyte; many refuse to conduct, and no decomposition can then occur; alcohol, ether, numerous essential oils, and other products of orfjanic chemistry, besides a few saline inorganic compounds, act in this manner, and completely arrest the current of a very powerful battery. It is a very curious fact, and well deserves attention, that very nearly, if not all the substances acknow ledged to be susceptible of electrolytic decomposition, belong to one class ; they are all binary compounds, containing single equivalents of their components, the latter being strongly opposed to each other in their chemical relations, and held together by very powerful affinities." " The metallic terminations of the battery, the poles or electrodes, have, in themselves, nothing in the sliape of attractive or repulsive power for the elements so often separated at their surfaces. Finely, divided metal suspended in water, or chlorine held in solution in that liquid, shows not the least symptom of a tendency to accumulate around them ; a single element is altogether unaffected, directly at least ; severance from previous combination is required, in order that this appear'-*'ce should be exhibited. It is necessary to examine the processes of electrolysis a little more closely. When a portion of water, for example, is subjected to decom- position in a glass vessel with parallel sides, oxygen is disengaged at the positive electrode, and hydrogen at the negative ; the gases are pure and unmixed. If, while the decomposition is proceeding, the intervening water be examined by a beam of light, or by other means, not the slightest disturbance or movement of any kind will be per- ceived, nothing like currents in the liquid or bodily transfer of gas from one part to another can be detected, and yet two portions of water, separated perhaps by an interval of four or five inches, may be respectively evolving pure oxygen and hydrogen." "If a number of different electrolytes, such as acidulated water, sulphate of copper, iodide of potassium, fused chloride of lead, &c,, be arranged in a series, and the same current be made to traverse the whole, all will suffer decomposition at the same time, but by no means to the same amount. If arrangements be made by which the quantity of the eliminated elements can be accurately ascertained, it will be found, when the decomposition has proceeded to some extent, that these latter will have been disengaged exactly in the ratio of ih* chemical equivalmtt. The same curreut which deconjposes 9 parts of t ^"^■ppf^ MOLKOULAR ELEOTRIOITT AND MATTER. 185 water will separate into their elements 166 parts of iodide of potas- sium, 139-2 parts of chloride of lead, Ac. Hence the very important conclusion : The action of the current is perfectly definite in its nature, producing a fixed and constant amount of decomposition, expressed in each electrolyte by the value of its chemical equivalent." From a very extended series of experiments, based on this and other methods of research, Mr. Faraday was enabled to draw the general inference that effects of chemical decomposition were always proportionate to the quantity of circulating electricity, and might be taken as an accurate and trustworthy measure of the latter. Guided by this highly important principle he constructed his voltameter, an instrument which has rendered the greatest service to electrical science. This is merely an arrangement by which a little acidulated water is decomposed by the current, the gas evolved being collected and measured. By placing such an instrument in any part of the circuit, the quantity of electric force necessary to produce any given effect can tie at once estimated ; or, on the other hand, any required amount of the latter can be, as it were, measured out and adjusted to the object in view. The voltameter has received , many differ -t forms; one of the most extensively useful is that ■ figured, ir which the platinum plates are sepai-ated by a very small interval, and the gas is collected in a graduated jar standing on the shelf of the pneumetic trough, the tube of the instrument, which is filled to the neck with dilute sulphuric acid, being passed beneath the jar." " The experiments of Mr. Faraday and Professor Daniell have given very great support to the chemical theory, by shewing that con- ' tact of dissimilar metals is not necessary in order to call into being powerful electrical currents, and that the development of electrical force is not only in some way connected with the chemical action of the liquid of the battery, but that it is always in direct proportion to the latter. *One very beautiful experiment, in which the decomposi- tion of iodide of potassium by real electrolysis is performed by a current generated without any contact of dissimilar metals can be thus made : — ^A plate of zino is bent at a right angle, and cleaned by 136 MOLEOULAR BLEOtRtOITT AMD MATTER. ,! nibbing with sand-paper. A platinum plate has a wire of the same metal attached to it by careAilly rivet- ting, and the latter bent into an arch. A piece of folded filter-paper is wetted with solution of iodide of potassium, and placed upon the zinc; the platinum plate is arranged opposite to the latter, with the end of its wire resting upon the paper, and then the pair plunged into a glass of dilute sulphuric acid, mixed with a few drops of nitric. A brown spot of iodine becomes in a moment evident beneath the extremity of the platinum wire ; that is, at the positive side of the arrangement. A strong argument in favour of the chemical view is founded on the easily proved fact, that the direction of the current is determined by the kind of action upon the metals, the one least attacked being always positive. Let two polished plates, the one iron and the ether copper, be connected by wires with a galvanometer, and then immer- sed in a solution of an alkaline sulphide. The needle in a moment indicates a powerful current, passing from the copper, through the liquid, to the iron, and back again through the wire. Let the plates be now removed, cleaned, and plunged into dilute acid ; the needle is again driven round, but in the opposite direction, the current now passing f^om the iron, through the liquid, to the copper. In the first instance the copper is acted upon, and not the iron; in the second, those conditions are reversed, and with them the direction of the current." , " The principle of the compound battery is, perhaps, best seen in the crown of cup«* ; by each alternation of zinc, fluid, and copper, the current is urged forward with increased energy, its intensity is augmented, but the actual amount of electrical force thrown into the current formf is not increased. The quantity estimated by its decom- posing power is in fact determined by that of the smallest and least active pair of plates, th« quantity of electricity in every part or section of the circuit being exactly equal. Hence large and small plates, battfiries strongly and weakly charged, can never be connected with- out great loss of power." <' When a battery, either simple or compound, constructed with pure or amalgamated xinc, is charged with diluted sulphuric acid, a • See pag* 168. t i.<.. The quantity of force rendered dynamic. MOIIOVLAB rOROK AND COMIPOUND MATTIE. 18T number of highly intcrteting phenomen* may be obtenred. While- the circuit remftine broken the tine ii perfectly ioMtiTe, no wAter i» decompoaed, no hydrogen liberated; but the moment the connection is completed, torrents of hydrogen arise, not flrom the line, but fhNn the copper or platinum surfaces alone, while the lino undergoes tranquil and imperceptible oxidation and solution. Thus, exactly the same effects are seen to occur in every active cell of a closed circuit which are witnessed in a portionof water undergoing electroly sis ; the oxygen appears at the positive side, with respect to the current, and the hydrogen at the negative ; but with this diflforenoe, that the oxygen instead of being set free combines with the line* It is, in fact, a real case of electrolysis, and electroly tea alone are availa- ble as exciting liquids." " From experiments very carefully made with a dissected battery ol peculiar construction, in which local action was completely avoided,, it has been distinctly proved that the quantity of electricity set in. motion by the battery varies with the zinc dissolved. Coupling this ftict with that of the definite action of the current, it will be seen that Fig. 73. MOLIOCLAR FOBCI AMD TBS MATUUAL ELXXBXTB Of OOMroUXD MiTtKR. * It may be therefore considered— a combustion of the sine in which a definite quantity of molecular force is set free in the form of molecular (voltaic) electricity, instead of in the form of beat (caloric force) as in ordbary combustion— which last may be termed, for the sake of distinc- tion, gaseous oxidation, the former being termed nascent or liquid oxida- tion. K 138 MOLICULAA FORCE AND COMPOUND MATTIB. whan a perfect battery of thia kind ia employed to deoompoae water, in order to evolve 1 grain of hydrogen fVom the latter, 33 graina of sine muat be oxidiied and ita equivalent quantity of hydrogen diaen- gaged in each active cell of the battery. That ia to aay, that the electrical force generated by the oxidation of an equivalent of line in the battery, is capable of affecting the decomposition of an equivalent of water, or any other electrolyte out of it." "The red oxide of mercury ia placed in a abort tube of hard glaaa, to which ia fitted a perforated cork, f\tmiahed with a piece of narrow glaaa tube, bent aa in the figure. The heat of a apirit lamp being applied to the aubetance, deeompoaitir a apeedily coinmencea, globules of metallic mercury collect in the cool part of the wide tube, which anawera the purpoae of a retort, while gas iaauea inconsiderable quan- tity fW>m the apparatua. Thia gaa ia collected and examined by the aid of the pneumatic trough, which conaiata of a veaeel of water pro- vided with a ahelf, upon which atanda the jara or bottlea destined to receive the gaa, filled with water and inverted. By keeping the level of the liquid above the mouth of the jar, the water ia retained in the latter by the preaaure of the atmoaphere, and entrance of air is prevented. When brought over the extremity of the gas-delivery tube, the bubbles of gas rising through the water collect in the upper part of the jar and displace the liquid. As soon aa one jar is filled, it may be removed, atill keeping ita mouth below the water level and another aubatituted. The whole arrangement is flhown in Fig. 73. The experiment deacribed ia.more inatructive as an excellent case of the resolution by simple means or flask furnished with a bent tube, a portion of the aalt called chlorate of potaaaa. A common Florence flaak answers perfectly well, the heat of a spirit lamp being sufficient. The salt melts and decomposes with ebulli. tion, yielding a very large quantity of oxygen gaa, which may be col- lected in the way above deacribed. The firat portion of the gas often contains a little chlorine. The white saline residue in the flask is chloride of potassium." These facts serve to show the intimate nature of the connection between chemical and electrical forces, i.e.f between those forms of force. CALORIC FORCE AND MATTER. We have adopted the term ' caloric-force ' as including the two distinct forms or modes of heat known as radiant •(or free) and la^t (or combined) heat. Of these, radiant heat may be considered as nearly allied to volumetric electricity and to light ; whilst latent heat appears to be more closely allied in its characteristics to molecular elec- tricity, for it enters into and modifies or changes the in- ternal physical condition of the compound matter. The inter-relation of these two forms of force, nair.:ly radiant and latent hea^^ has to be now briefly considered. Note. — ^It may be observed that the phenomena of latent heat (and of specific heat) together with those of isomorphism, strongly support the proposition that com- pound matter consists of elementary matter compounded with force. Fowne^s Chemistry.— HeeA. ..Chmge of state. "If equal weights of water at 32°, and water at I74<*, be mixed, the temperature of the mixture will be the mean of the two temperatures, or 108°. If the same experiment be repeated with anow, or finely powdered ice, at 3V and water at 174" the temperature of the whole will be still only 37P, but the tee will have bem melted. 1 iJ:;f::!St!i?S: }=»»••«•'"•' "'• 1 lb. of ice at 32°. > _ I lb. of water at 174° :;} = 2 Iba. water at 32'. In the last experiment, therefore, as much heat has been appa- rently lost as would have raised a quantity of water equal to that of the ice through a range of 142°. The heat thus become insensible to the thermometer in effecting the liquefaction of the ice, is called latent heat, or better, heat of fluidity. Again, let a perfectly uniform sou-ce of heat be imagined, of such .intensity that a pound of water placed over it would have its tempera- 1 I! 140 CALORIC FORCI AND MATTXR. ^ ' ture rkised 10" per minute. Starting with water at 32", in rather mor»- than fourteen niinutea its t>>mperature would have risen 142" ; but the same quantity of ice at 32", exposed for the same int<«rval of time would not have its temperature raised a single degree. But, then, it would have become water ( the heat received would have been ezclu> eively employed in effiecting a change of state. The heat is not lost, for when the water freezes it is again evolved. If a tall jar of water, covered to ezclode dust, be placed in a situation where it shall be quite undisturbed, and at the same time exposed to- great cold, the temperat'^'^e of the water may be reduced 10° or more below its freecing-poin .ithout the formation of ice t but then if a little agitation becommunicated to the jar, or a grain of sand dropped into the water, a portion instantly solidifies, and the temperature of the whole rises to 32°; the heat disengaged by the iVeeeing of a small portion sf the water will have been suiBoient to raise the whole con- tents of th« jar 10"." " The law thus illustrated in the case of water- is perfectly general. Whenever a solid becomes a liquid, a certain fixed and definite amount of heat disappears or becomes latent ; and conversely, whenever a liquid becomes a solid, heat to a correspond- ing extent is given out. The amount of latent heat varies much with different substances, as will be seen by the table :— Water 142° Sulphur 145° Lead 162° Zinc 193° Tin 600° Bismuth.: 600° A law of exactly the same kind as that described afifectsuniversally the gaseous condition { change of state from solid or liquid to gas is accompanied by absorption of sensible heat, and the reverse by its disengagement. The latent heat of steam and other vap<^nirs may be ascertained by a similar mode of investigation to that employed in the case of water. When water at 32° is mixed wiiu an equal weight of water at 212° the whole is found to possess the mean of the two temperatures, or 122° ; on the other hand, 1 part by weight of steam at 212- when con- densed into cold water, is found to be capable of raising 6-6 parts ot the latter from the freezing to the U>iling point, or through a range of 180°. Now 180-{-&'6=1003; that is to say, (team at 212° in becoming water at 212°, parts with enough heat to raise a weight of water equal to its own (if it were possible) 1008° of the thermometer. When water passes into steam, the ^ame quantity of sensible heat becomes latent." CALORIO rORCI AMD MATTIB. 141 ""It iaa very remarkable fact, that the latent heat of steantilimininhes afl the temperature of steam riees, no that equal weight* o f ateani -thrown into cold water exhibit nearly the same heating power, al< though the actual temperature of the one portion may be 212° and that of the other 360°. Thia also appears true with temperatures below the boiling point : so that it seems to evaporate a given quantity of water ^the same absolute amount of heat is required, whether it be performed slowly at the temperature of the air, in a manner presently to be noticed, or whether it be boiled off under the pressure of twenty at- »no..jhereB." CapaeHy far Heal; Spfi fie Etat. "Let the reader renew a supposition made when the doctrine of latent heat was under consideration ; let him imagine the existence of an uniform source of heat, and its intensity such as to raise a given weight of water 10° in 30 minutes. If, now, the experiment be re- peated with equal weights of mercury and oil, it will be found, that in- stead of 30 minutes, I minute will suffice in the former case, and 15 minutes in the latter. This experiment serves to point out the very important fact, that different bodies have different eapaeiiiet for h«al; that equal weights of water, oil, and mercury, require, in order to rise through the same range of temperature,— quantities of heat in the proportion of the numlMTS 30, 16, and 1. This is often expressed by flaying th^t the ipeeifie heat of water is 30 times as great as that of mercury, and the specific heat of oil 16 times as great." " MM. Dulong and Petit observed in the course of their investig- ation a most remarkable circumstance. If the specific heats of bodies be coniputed upon equal weights, numbers are obtained, all different, and exhibiting no simple relationH among themselves ; but if, instead of equal weighto, quantities be taken in the proportion of the chemical equivalents, an almost perfect coincidence in the numWrs will be observed, shewing that some exceedingly intimate connection must exist between the relations of bodies to heat and their chemical nature." CALORIO FORCE AND MBCBAN'IOAt IPrECT. The following, taken also from Fotcne^ Manual of Chemistry f are instances of the correlation (inter-relation) of caloric-force and mechanical eifect. •'"^l 142 CALoaio roRoi and uiohanioal crrioT. « An experiment of Court Rutnford is on record, in which the heftt developed by the boring of • brMi cannon wm euffioient to bring to tiie boiling point two and • half gallons of water, while the duet or alkavings of metal, out by the boror, weighed a ftw ounces only," " Sir H. Davy melted two pieces of ice by rubbing them together in vacuo at 82° i and uncivilised men, in various parts of the world, have long been known to obtain Are by rubbing together two pieces of dry wood." " A soft iron nail may be made red hot by a few dexterous blows on an anvil ) but the experiment cannot be repeated until the metal has been annealtd, and in that manner restored to its original physical state." To these examples may be added, that of the heat given out by air and other gas when subjected to mechanical pressure,* and that of the steam-engine, in which a por- tion of the heat imparted to the water may be considered to be converted into mechanical efTect. f Magnetism. — The phenomena belonging to what is termed magnetism are to be considered as included under the more general title molecular electricity. They are, however, advantageously studied as a separate class or subdivision. For the purpose of distinguishing this division of the one form of force into two kinds of manifestation, the 'The ' caloric-engine ' (of Eridon) in which the expansion of air by heat famishes the motive power, may 1 e mentioned as another illustration. t A little consideration will mai a apparent that a distinction should be made between the case of a high-pressure, and of a condensing engine ; in the former the sensible (radiant) heat, which is contained in the steam above the temperature of 2139 and occasions the pressure in exoeu of atmospheric pressure, may be considered as directly converted into mech- anical efbct ; in the latter (the condensing engine) the latent heat con- tained in the iteam through condensation of the steam and production of the vacuum, is, so to ipeak, indirectly converted into and utilised u- mechanical effect. OALORIO rOROI AND MlCRANirAT. KFriCT. 148 term ' magnetism ' might be amplified into magnetic electricity, and molecular electricity be considered to / Voltaic or Chemical electricity, { Magnetic electricity. The one class of phenomena belongs to the investiga- tion of the influence of molecular electricity upon the elementary constituents of which compound mutter is compounded, and the circumstances under which that influence causes those elements to combine or to separate. The other class — that of magnetic electricity — belongs to the investigation of the physical influence of electri- city on the various descriptions of compounded matter. That magnetism is a manifestation of molecular (voltaic) electricity, is shown by the following : — • Fownu' Jfanval of Chemutry , ■ ■> Page 96. " A little consideration will show that, flrom the peculiar nature of the electro-dynamic force, a wire carrying a current, bent into a spiral or helix, must poseees the properties of an ordinary magnetized bar, its extremities being attracted and repelled by the poles of a magnet. Such is really found to be the case, as may be proved by a variety of arrangements, among which it will be suffi- cient to cite the beautiful little apparatus of Professor De la Rive : A short wide glass tube is fixed into • cork ring of considerable size ; a little voltaic battery, consisting of a aingle pair of copper and zinc plates, is fitted to the tube, and to these the ends of the spiral are soldered. On filling the tube with dilute acid and floating the whole in a large basin of water, the helix will be observed to arrange itself in the magnetic meridian, and on trial it will be found to obey a magnet held near it in the most perfect manner as long as the current cir- culates." 144 MAONKTIO AND VOLTAIC ILKOTaiOITT. " W^hen an electric current ia pMsed ftt right angles to a pie^e ot iron or steel, the latter acquires magnetic polarity j either tem^/orary or permanent, as the case may be, the direction of the current determining the position of the poles. This effect is prodigiously increased by car.sing the current to circulate a number of times round the bar, which then acquires extraordinary magnetic power. A piece of soil iron, worked into the form of a hor8e*shoe, and surrounded by a coil of copper wire covered with silk or cotton for the purpose of " insulation, furnishes an excellent illustration of the inductive energy in this respect ; when the ends of the wire are put into communication with a small voltaic battery of a single pair of plates, the iron instantly becomes tj highly magnetic as to be capable of sustaining a very heavy weight. A current of electricity can thub develop magnetism in a transverse direction to its own ; in the same manner magnetism can call into activity electric currents. If the two extremities of the coil of the electro-i..'«^et above described be connected with a galvanoecope, and the iron magnetized by the application of a permament steel horse-shoe magnet to the ends of the bar< a momentary current will be developed in the wire, and pointed out by the movement ! Fig. 72. :iAONITIO AND VOLTAIC ILECTHICITY. US of the needle. It Ihsts but a single instant, the needle returning after a few oscillations to a state of rest. On removing the magnet, whereby the polarity of the iron is at once destroyed, a seeoni current or wave will become apparent, but in the opposite direction to that of the first. By employing a veiy powerAil steel magnet, surrounding its iron keeper or armat»ir« with a very long coil of wire, and then making the armature its-^.f rotate in front of the faces of the magnet, so that its polarity shall be rapidly reversed, magneto-electric currents may be produced, of such intensity as to give bright sparks and most power- ful i^hocks, and exhibit all the phenomena of voltaic electricity. Fig. 72 represents a very powerful arrangement of this kind." " When two covered wires are twisted together or laid side by side for some distance, and a current transmitted through the one, a momentary electrical wave will be induced in the reverse direction, and on breaking connexion with the battery, a second single wave will become evident by the aid of the galvanoscope, in the same direction as that of the primary current." Lardner'a Natural PAi'2o«qpAy.— Magnetism by induction. (1630.) "Soft Kon rendered temporarily magnetic.'-U the poles of a magnet, this bar will itself become immediately magnetic. It will manifest a neutral line and two poles, that pole which is in contact with the magnet being of a contrary name to the pole which it touches. Thus if A. B., Fig. 462, be the bar of sofl iron which is brought in contact with the boreal pole 6. of the magnet a.h., then ^. will be the austral and B, the boreal pole* of the bar of soil iron thus rendered * The term austral is applied (by Lardner, 1656) to the pole of the mag< net which points towards the north pole of the earth, and boreal to the opposite pole of the magnet which points to the south. The expressions so applied are somewhat likely to cause misunderstanding. In the case of rol- umetric electricity, we do not. think the theory of two distinct forces or forms of force is, in the present state of scientific knowledge, unreasonablu although we arc strongly of opinion that tiie facts will be found eventually not to support that theory. In applying the same theory or a modification of it to the case of magnetism there would not be, we opine, the same reasonableness. The fact that a coil of wire which is conducting voltaic electricity displays the properties of a magnet (as in De La Rive's apparatus, described by Fownes) and the fact, stated (Art. 1634) by Lard- 'jC-i 146 MAGNETISM. magnetic by contact, and E. will be its equator, whicli, howcrcr, will not be the middle of the bar, but nearer to the point of contact." " Theetate of the bar A. B. can be rendered experiiiientally mam est bj any of the testa already explained. If it be rolled in iron filings, they will attach themselves in two tufls separated by an in- termediate point which is free from them ; and if the test pendulum * be successively presented to different points of the bar, the varying intensity of the attraction will be indicated." " If the bar A. B. be detached from the magnet, it will instantly lose its magnetic virtue. (1631.) "It is not necessary, to produce these effects, that the bar of soft iron should be brought into actual contact with the pole of a magnet. It will be manifested, only in a lessdegree, if it be brought into proximity with the pole without contact. If the iiM A. B. be presented at a small distance from the pole b., it will manifest mag- netism in the same manner ; and if it be gradually removed from the pole, the magnetism it manifests will diminish in degree, until at length it wholly disappears." (1634.) "It might be supposed, from what has been stated, that if a magnetic bar were divided at its equator, two magnets would be produced, one having austral and the other boreal magnetism, so that one of them would attract an austral and repel a boreal pole, while the other would produce the contrary attraction and repulsion. This, however, is not found to be the case. If a magnet be broken in two t>' its equator, two complete magnets will result, having each an quator ^t or near the centre, and two poles, austral and boreal ; and if these be again broken, other magnets will be formed, each having ner himself, that if a magnet be divided each of the parts is a complete magnet i,i itself (i.«., having an equator and two poles), taken together controvert luch a supposition. • A small ball of iron suspended by a fibre of silk. The ball is attracted or repelled out of the perpendicular when brought near to the respective poles of the magnet. MA0NBTI8M. 14T an equator and two poles as before ; and in the same manner, what, ever be the number of parts, and however minute they be, intowliich a magnet is divided, each part will still be a complete magnet with an equator and two poles."* Fig. 26. (1638.) " Ilff'ect of induction on hard iron or tUel.—h a bar o hard iron or steel be placed with its end in contact with a magnet in the same manner as has been already described with respect to soft iron, it will exhibit no magnetism ; but if it be kept in contact with the magnet for a considerable length of time, it will gradually acquire the same magnetic properties ae have been described in respect to bars of soft iron, with this difference, however, tltat having thus acquired them, it does not lose them when detached from Jie magnet, as is the case with soft iron. Thus it would appear, tiiat it is not literally true that a bar of steel when brought into contact with the pole of a magnet receives no magnetism, but rather that it receives magnetism in an ibsenaible degree { for if continued contact impart sensible magnetism, it must be admitted that contact for shorter intervals must impart more or less magnetism, since it is the accumu- lation of the effects produced from moment to moment that the sensi- ble magnetism manifested by continued contact is produced." (1642.) " A red heat destroys the magnetism of iron. If a magnet, no matter how powerful, natural or artificial, be raised to a red heat. * VTe would suggest for consideration, whether sufBcieat prominence has been generally given to the full significance of this fact. The statement is definite and distinct, and when fully appreciated a clearer understand- ing of the character of the magnet is at once obtained ; ii becomes evi- dent that the magnetic ef%ct of the whole is the collective eflfect (or the sum of the efOicts) of the parts aclinc together, the effect of each particle augmenting the effects of the others. Hence the molecular mode of the oret becomes at once distinctly apparent. The abore illustration, Fig. 26, is fiom Fownes' Manual of Cbemiitry. 148 MAONBTIBM. it will lose altogether ita magnetic virtue.* The elevation of tempe- rature and the molecular dilatation consequent upon it, destroys the coercive force and allows the recombination of the magnetic fluid. When after such change the magnet is allowed to cool, it will continue divested of its magnetic qualities. These effects may, how- ever, be again imparted to it by the process already mentioned." Magmthaiion of Light and Diormagnetitm. Encyclopedia Britannica, Chap. III., Sect. III.— "In the year 1846, Dr. Faraday discovered that when magnetic currents, or, as he expresses it, lines of magnetic force, pass through certain bodies, they communicate to these bodies a certain magnetic condition, which, in transparent bodies, is analagous to rotatory double refiraction and polarisation, and which in other bodies is the reverse of that which takes place in iron, nickel, and some other metals. If a parallelepiped N. S. n. «. of heavy flint glass, 2 inches square and i inch thick, and having no action on polariied light, is placed, as in the figure, on the poles N. S. ofapowerAil electro-magnet y. C. S., and a strong galvanic current passed through it in the direction of S. N., the glass will neither be attracted nor repelled, but is found to have received while the current is passing through it, such a struc- tiire,t resembling that of quartz and certain fluids, as to turn the * (169S.) "It appears that a magnetic bar when raised to a red heat does not lose its magnetism suddenly at that temperature." And, when plunged into boiling water and retained there for ten minutes, it loses a part of its magnetism, and if again replunged another portion, and so on but still retaining a portion after seven or eight immersions. It is not quite apparent whether Sir D. Brewster i: :n.,v3 ' t i'ois stale- ment that an alteration or modification in the wr\:r.;rrjMi\t ci %'m wr' trial particles of the substance takes place in it whilst uudvr t'j > icf.uartco cf C-9 magnet ; supposing the expression of tvM'a supposlt^o i u tHi : ai -id m, • '. ut sot, we opine, supported by the erideuce of the ezpiuiu^u; , x>n the con- trary, the fact of the immobility of the particles in the solid gl/i-:: >. opposed MA0NBTI8M. U9 plane of apolarind ray in the Mme direction m the current. If the polarized ray ie transmitted through the upper and under faces H. O. no effect whatever is produced. The rotation of the plane of polari- zation is firom Itf* to right when the ray enters the Ikce «. n. and the observer looks into the face n. *., and from right to 10 when the ray enters n. «., and the observer looks into «. n. This is a very remark- able fact, ae the direction of rotation is the same in rock-crystal and other bodies through whatever side the light enters. The intensity of the rotatory-force depends upon the strength of the galvanic current, and upon the length of the piece of glass. When the ray, by reflections at n. and a. was made to pass three or Jive time* through the length n. «. of the glass, the effect was increased three or five times, juet as in rock-crystal it is increased by increasing the thickness of the plate." Fcraiay't Biography, by Profeuor TyndallA Page 84. " He showed that when a polarized ray passed through his heavy glass in a direction ^rallel to the magnetic lines of force, the relation is a maximum, and that when the direction of the ray is at right angles to the lines of force, there is no rotation at all. He also proved that the amount of the rotation is proportional to the length ot the diamagnetic through which the ray passes, He operated witli liquids and solutions. Of aqueous solutions he tried 160 and more, and found the power in all of them. He then examined gases ; but here all his effortt to produce any sensible action on the polarized beam were ineffectual. He then passed from magnets to currents, enclosing bars of heavy glass, and tubes containing liquids and aque- ous solutions within an electro-magnetic helix. A current sent through the helix caused the plane of polarization to rotate, and always in the direction of the current. The rotation was reversed whiin the current was reversed. In the case of magnets, he observed a gradual, though quick, ascent of the transmitted beam from a state of darkness to its maximum brilliancy whef) the magnet was excited. In the case of currents, the beam attained at once its maximum. This to the acceptance of such Bupposition ; and, moreover, it is a reasonable inference that any such structural alteration in the matter of the substance would be directly cognizable in other ways, and it is not shown that such structural alteration has been cognized in other ways. t ' Faraday as a discoverer.' 160 MAOiriTlO rOBOE. h« Bkowed to be due to the Hnu required by the iron of the electro- magnet to Heume its full mkgnetio power, which time vanishes when a current, without iron, is employed. ' In this experiment,' he says, ' we may, I think, justly say that a ray of light is electrifleii, and the electric forces illuminated.' In the helix, as with the magnet!>, he submitted thecoin was repelled, the revulsion being so vio- lent ab to cause it to spin several times round its axis of suspension . A tUbtrgroaehm similarly suspended exhibited the same deportment. For a moment I thought this a new discovery ; but on looking over the literature of the subject, it appeared that Faraday had observed, mul- tiplied, and explained the same effect during his researches on dia- magnetism. His explanation was based upon his own great dis- covery of magneto-electric currents. The effect is a most smgular one. A weight of several pounds of copper may be net spinning l)etween the electro-magnetic poles ; the excitement of the magnet infltantly stopo the rotation. Though nothing is apparent to tlie eye, the copper, if moved in the excited magnetic fleld, appears to move through a viscout* fluid ; while, when a flat piece of the metal is caused to pass to and fro like a saw l)etwe«;n the polc», the Hawing of the magnetic field reeenibles the cutting through of cheeHe or butter. MAONBTIO FOaCB. f|f This virtual /riW/o/i of the magnetic field is do strong, that copper, l.y ita rapitl rotation between the poles, might probably be ftised. We may easily ilinmiss iIiIh experiniput l.y saying that the heat la due to the electrieenmotvajMiM ift «MMppM>. Bat m Utng as we are unable to itfri^.to '^^^^^ * '^ ^• •» tlMtrio Ottmnt?' the I'xplanatioa '» ^"^^f^MlP' ^ l»7 «»B put, I look with pro- found inteittt >'all|ll^||pllMi»|| Mfidn Imn nfrmd to." lfil6. «'^*to iJli|N#fii» Md «k« mying attrMtion of the parts ot .he Hurt-aater frame, they will dispose themselves into reguiiir linos, stretchinjr from one pole of the magnet to the other, following the course of tlie magnetic curves and exhibiting them beautifully to the eye. This ef!ipct is shown in the annexed Fig. 50, where N. and (S. art* the poles of the ma^rnet iV .'.'., »i.h. l)eing the mean line where no filings adhere. Tlie same arrangement is also produced when the magnet is held above tbe paper cofjtaiiiin>r the filings. In the case of inoUiced magnrtisni, the fcteel filings arranjre them- selves in curves round the iron on which the magnetism is induceou thix in laid a circular metallic dise C, rather lesn in diameter than A, B., having a glaHH handle. Before applying the dine C. the resinous surface is electrified nega- tively by atriking it several times with the fur of a cat. The diao C, being then applied to the cake A. J9.,and the finger being at the aame time presaed upon the disc C. to establiHh a communication with the ground through the body of the operator, a decomposition takes place by the inductive action of the negative fluid on the resin. The negative flukl eecapea firom the diao C -through the body of the operator to the ground, and a poaitive charge remains, which is prevented tVoni pass- ing to the resin partly by the thin film of air which will alwaya remain between them^ven when the plate C, rests upon the reaia^iknd partly by the non-conducting virtue of the resin. When the disc C. is thus charged with positive electricity, kept latent on it by the influence of the negative fluid on A. B., the finger being previously removed fVom the disc C, let it be raised ftrom the • For further Uloatrationa of magnetic curves, see Appendix. f' THS rarsicAt roRctt. 165 rMin, Md the eleetricitjr upon it, befora diaaimulated, will become free •nd IMJ be imported to any influUted conductor adnpted to receive it. The charge of iiegntive electricity renwiniug undiminiahed on the reein A. B., the operation may be indefinitely repeatetj ; no that an inanlated conductor may therchr be charged to any extent, by giving .to it the electric fluid drop Ly drop thus cvulv«>d on the diao C. Iiy the inductive action of A. B." Keeping in mind the relationship of the several physi- cal forces as ' forms' ur ' modes ' of the one primary force, the significance of the result thus obtained by the induc- tive action of the electrophorus, in connection vi'ith the other observed facts of volumetric electricity, may be left to the attentive consideration of the reader without further comment than to note that herein we have a mode of disturbance by which a continuous and inex- haustible supply of free force can be (und is) obtained ; inexhaustible, because it consists in a conversion of latent into free force, which, being removed, is replaced from the common r^Nervoir of force, into which, again, that quantity removed from the surface of the material body, must necessarily find its way. ... It is, thereforo, a continuous circulation of force, which force in its circu- lation is capable of producing by its action, an unlimited amount of effect on material bodies ; . . . meaning there- by, an effect in its extent and character proportional only to the quantity and intensity of the force employed, but of which the supply is unlimited. Having now brought togethor, from the record, a suffi- cient number of the natural (observed) facts to illustrate the relationship of the several forms of force ; it is desi- rable to particularly caution the reader with respect to the relation of matter and force. ... On the one hand, xiot to invest matter with imaginary properties which do IMAGE EVALUATION TEST TARGET (MT-3) 1.0 I.I 11.25 |j25 1^ U i|L6 6" Photographic Sciences Corporalion 23 WIST MAIN STRUT WIBSTIR,N.Y. MSM (716)172-4303 ^^^^^m^m:^:::: 156 THE * SPmiTUAL ' AND THE ' MATERIAL.' not belong to it, and, on the other hand, not to con- found reasoning by doubting the reality of those proper- ties and characteristics which do belong to matter and things material, and which distinguish it from spirit and things spiritual. . i ; . ,, In a scientific sense, i.e., a correct sense, the meaning attached to matter should include all those things which- we clearly recognize as belonging distinctively to matter^. {i.e., to that which is so-called), and should include nothing else ; consequently the word ' matter ' should be a collective expression for those properties and char- acteristics of which it consists ; and, therefore, to fully and correctly apprehend and describe all those properties and characteristics which pertain to matter, is to give a comprehensive and correct definition of the word ' matter. ' A dispute, controversy, or argument, as to certain of the properties alleged on the one side and questioned on the other, to belong to matter, is a dispute or an argument as to the correct definition of the word, and which definition, if shown to be incorrect or defec- tive, may be amended accordingly. To deny the exist- ence or reality of matter is simple folly ; for why should not the word * matter ' be a? good as any other word to denote those things or that c^ass of existent things which. must be denoted by some collective expression. But if we are justified in the generalization with respect to the various physical forces which has been now put before the reader, the question then suggests itself, whether matter is not also referable to the primary force, or, in other words, whether matter is not itself a form of force, differing only more essentially from each THE spiritual' and the 'material.' 157 and all the other forms of force, known to us, than those •other forms of force differ from each other. The supposition being entertained, accordingly, that mafier is, strictly speaking, a distinct fundamental form offeree, differing from that fundamental or collective form which we have denominat sd Electric Force. The relationship may be thus formulated : The various Forces (modes or forms of Force) known to [physical science. f The various descriptions of J elementary matter known to I chemistry. ■ r The phenomena of the -Active Force manifested J material world ; . . . . state of on Matter. | motion, gravitation, incandes- [cence, &c., &c. The various conditions or Free (Electric) Force. Materialized Force - (or Fixed Force.) I, Xatent Force combined ! molecular states of matter, with Matter. ■ i.e., the solid, fluid, gaseous I condition. • ^ If we adopt this as a theory, or assume it to be an .approximately correct explanation, we shall find therein cause to look upon matter as particularly connected with •our8elve8,because entering into our organization as human beings, and appearing to our material senses to constitute nature. (Constituting, in fact, that which we term nature.) But, viewing the subject in this relationship, we are ablt to perceive that . . in a spiritual (or universal) sense . . we ought to consider matter, {i.e., the material world) as comparatively artificial, by which we mean, as a restricted 158 THE NATURAL WORLD, AND THE UNIVERSE. and limited form of that which is in its primary nature unrestricted and unlimited. Or, to express the same meaning otherwise, we ought to consider that those forces . . . which in a universal or celestial sense may be termed, in their primary condition, natural ... are in the material world materialized and adapted to a particular and limited purpose . . . that purpose including a special res- triction within certain definite limits and boundaries, of forces which ore in their primary nature unrestricted and unlimited. Both are actually existent ... the spiritual and the material ... and both are consequently real. It would not, therefore, be correct to speak of the one as the shadow of the other ; nevertheless, the material reality being de- rived from and dependent upon the spiritual, and being limited and restricted to certain conditions, the material reality does represent the shadow or the reflected image (so to speak) of the unlimited spiritual reality of which it is (may be said to be) a modification. We believe that the form of self-deception or prejudice called 'materialism' has now (in a greater or lesser degree) so strong a hold on the minds of even educated persons that it will, at first, appear to many like stating a paradox to make the assertion that the actual inter-relation of spiritual and natural reality is such that the material world (i.e., matter in its variousforms constituting that which we call nature,} occupies a relationship to the spiritual world somewhat akin to that which the shadow bears to the substance. We believe that to many this will be calling upon them to reverse their preconceived notions about natural reality ; but it necessarily follows that such is the char- acter of the actual relationship D3tween ' material ' and * spiritual ' reality, if the explanation we have given of ihe THE NATURAL WORLD, AND THE UNIVERSE. 159 nature of the physical forces and of matter, be accepted as approximately correct, . . . and we say that, by the rules of sound science, that explanation must necessarily be 80 accepted. -^ Note. — To those persons who are desirous to correctly understand this relationship and who find a difficulty in following the argument, we wish to point out the neces- sity of carefully examining, in the first instance, the pre- cise value of the meaning which they themselves attach to the most prominent terms here made use of, and especially to the words * nature ' and ' matter.' The word ' matter ' having been defined, the entire argument or explanation of the subject might be very well put in the form of a definition of the word ' nature,' or, on the other hand, the meaning of the word 'i^ature' may be restricted and limited to that material sense in which it is usually understood and used, but if so, then, let those who use it in that sense be mindful that its meaning is so restricted, viz., that it is used in a material sense only and not in a general or absolute .sense. It may assist some persons, perhaps, to suggest the use of the compound terms 'Material-Nature' and 'Spiritual-Nature.' It may be then understood that ' Material-Nature ' belongs to a part of creation having a special and distinct purpose j and being, therefore, an adaptation, in which the properties and characteristics of the elementary parts are limited and restricted by special and distinct laws framed expressly for the uniform and harmonious regulation of those parts under the limiting and special conditions to which the material world was to be subjected, it may be apprehended without much difficulty that * Material-Nature' is, in a more general i : I I' 160 CONCLUSION. i or spiritual sense, artificial ; because it is an adaptation having a special and limited character ; nevertheless, be it carefully noted that, all the parts of thii, distinct part of creation (i.e., of the material world, or of ' nature' as usually understood,) are real and true, not only in a material, but also in a spiritual sense. The plan upon which this distinct part of creation is arranged and the laws by which it is regulated. . . although arbitrary in the sense of limiting and restrict- ing the elementary and compounding parts to the con- ditions assigned them in the plan, ... are not to be considered arbitrary in any other sense ; there is no reason whatever to infer, and it is not to be inferred, that the reality and truth of the material world are not in harmony with, or that they are not a part of, the reality and truth of the spiritual world. We come now to the conclusion of a work which commenced with a reference to the author of the ' great instauration.' The purpose of this our undertaking is in a great measure the same as that which he had in view, namely, to separate sound and wholesome knowledge from the pernicious influence of that corrupt philosophy and unsound knowledge with which it was then, as it is- now again becoming more and more, contaminated. Much of his work was almost necessarily, and most ad- vantageously, occupied in teaching the method of scien- tifically classifying knowledge. • • .i.e., of separating and arranging, into an available and useful form, the hetero- geneous and disorderly collection of knowledge which at that time obtained. "For a long time past this part of CONCLUSION. 161 Bacon's system has been fully in use, and it is now well understood and practised ; therefore, since it is needless to teach what is already known, the two v/orks will necessarily appear to differ very much in form. We believe, however, that the method adopted will be found on investigation to be essentially the same in both. However this may be, we know, at least, that the pre- sent work has been undertaken and carried out in the same spirit in which we believe that his was accom- plished, and we have the same hope and desire that our work will commend itself to the acceptance of those for whose benefit it is intended, which he expressed and doubtless felt. We will, therefore, conclude by express- ing, in his words, feelings which we share with him, and by dedicating, in his words, this our work, in reverence, gratitude and confidence, to Him without whose aid and approval the wisdom of the cleverest man is but foolish- ness. .."May Thou, therefore, Father, who ga vest the light of vision as the first fruit of creation, and who hast spread over the fall of man the light of Thy understand- ing as the accomplishment of Thy works, guard and direct this work, which issuing from Thy goodness, seeks in return Thy gloiy ! When Thou hadst surveyed the works which Thy hands had wrought, all seemed good in Thy sight, and Thou restedst. But when man turned to the works of his hands, he found all vanity and vexation of spirit and experienced no rest, if, however, we labour in Thy works, Thou wilt make us to partake of Thy vision and Sabbath ; we, therefore, humbly beseech Thee to strengthen our purpose, that Thou mayst be willing to endow Thy family of mankind with new gifts, through our hands, and the hands of those in whom Thou shalt implant the same spirit." Ill <-*,-,.*■■- :■■■■!- Append ix :p, ;i*- (1.) Eclipses and Occultations of Jupiter's Satellites, Merschel's Outlines of Astronomy. (537) " These eclipses (of Jupiter's satellites) moreover, are not seen, as is the case with those of the moon, from the centre of their motion, but from a remote station, and one whose situation with respect to the line of shadow is variable. This, of course, makes no difference in the times of the eclipses, but a very great one in their visibility, and in their apparent situations with respect to the planet at the moments of their entering and quitting the shadow." (538) " Suppose S. to be the sun, E. the earth in its orbit, E. F. G. K., J. Jupiter, and a.h. the orbit of one of its satellites. The cone of the shadow, then, will have its vertex at X., a point far beyond the orbits of all the satel- lites ; and the penumbra, owing to the great distance of the sun, and the consequent smallness of the angle (about 6' only) its disc subtends at Jupiter, will hardly extend, with- in the limits of the satellites' orbits, to any perceptible distance beyond the shadow — for which reason it is noC represented in the figure. A satellite revolving from west to east (in the direction of the arrows) will be eclipsed when 164 APPENDIX— Jupiter's hatellites. ■" it enters the ishadow at a., but not suddenly, because, like the moon, it has a considerable diameter seen from the planet ; so that the time elapsing from the drat perceptible loss of light to its total extinction will be that which it occupies in describing about Jupiter an angle equal to its apparent diameter as seen from the centre of the planet, or rather somewhat more, by reason of the penumbra ; and the same remark applies to its emergence at b. Now, owing to the diflference of telescopes and of eyes, it is not possible to assign the precise moment of incipient obscuration, or of total extinction at a., or that of the first glimpse of light falling on the satellite at b., or the complete recovery of its light. The observation of an eclipse, then, in which •only the immersion, or only the emersion, is seen, is in- ■complete, and inadequate to afford any precise information, theoretical or practical. But, if both the immersion and «mersion can be observed with the same telescope and by the same person, the interval of the times will give the duration, and their mean the exact middle of the eclipse, when the satellite is in the linQ S. J. 2C,, i.e., the true moment of its opposition to the sun. Such observations, and such only, are of use for determining the periods and other particulars of the motions of the satellites, and for the calculation of terrestrial longitudes. The intervals ©f the eclipses, it will be observed, give the synodic periods * of the satellites' revolution ; from which their siderial periods must be con- tina,the spots of light simply des- cribe a series of parallel luminous lines upon the screen, the length of • How has this been proved ? in APP«»n>TX— THB ETHXK. these lines marking the ampyitude of the vibrKtion . The imprefloion of wave-motion has totally disappee:*ed." « The most fiimiliar illusiration of the interference of sound waves is furnished by the beuis produced by two mutiiGal sounds slightly out of unison. These two tnning-fbrks are now in perfect unison, and when they are agitated together the tvro sounds flow writhout rough • ness, as if they were but one. But by attaching to one of the fbrks a tw crest coincides with crest, sinus with sinus, and the two systems blend together to a single system of double amplitude. If both series start at the same moment, one of them being, at starting, a whole wave-length in advance of the other, they also add themselves i. 172 APPINDIX— TBI XTHIB. together, and we have an augmented luminous effect. Jnet aa in the case of sound, the same occurs when the one system of wares is any ectn number of semi-undulations in advance of the other. But if the one system be half a wave-length, or any odd' number of half wave- lengths in advance, then the crests of the one fall upon the sinuses of the other; the one system, in fact, tends to lift the particles of ether at the precise places where the other tends to depress them { hence, through their jomt action the ether remains perfectly still. This stillness of the ether is what we call darkness, which corresponds, aa Alreadly stated, with » dead level in (h« oase of water.". \i APPENDIX TO TR> MANIFESTATIONS OF FOBOB. MAONIiTO-BLEOTBIO FOBOB. ^Uneyelopedia BrUannica, Chap. VII., See. III., Art. MagneUum, —Dr. Boget gives the following interesting account of the phenomena which take place by continuing to agitate the filings when thej ar' arranged as in Fig. 53 : " By continuing to tap upon the paper," says he, *' the filings arrange themselves still more visibly into separate lines ; but here a curious and perhaps unlooked for phenomenon presents itself. The lines gradually move and recede from the magnet, appearing as if they were repelled instead of attracted, as theory would lead us to ex- pect. This arises from the circumstance, that each particle of iron, or cluster of particles, is thrown up into the air by the shaking of the paper, and while unsupported, immediately turns on its centre, and acquires a position more or less oblique to the plane of the paper. This is shown in Fig. 63, in which M. represents a section of Mie magnet, P. P. a section of . the paper, and/, /.the position of the filaments of iron thrown up into the air. The end of each fila- ment nearest to the magnet is thus turned a little downwaids, and the filament falls upon the paper at a point a little more distant than that which it before occupied ; and thus, step by step, it moves farther and farther from the magnet, till it reaches the edge of the paper and ftUs oflf." :■*;■' 174 HAaNXTIO OURVKS. magnet, instead of being beneath the paper, is held just the reverse. In this latter case, the lower "When above it, tfa ends of the filaments having a tendency to turn towards the mag- net, the filings gradu- ally collect under it, when made to dnnce by the vibrations of the pa- '°' per, instead of falling outwards as they did before. This will be seen in Fig. 64, where the letters have the same indications as in Fig. 63." " A different set of magnetic curves is produced when two similar poles, for example, two north poles, as shown in Fig. 66, (PI. 11,) are placed near each other. These curves are called divergent cnrveBf aud may be exhibited by iron filings like the convergent ones. Dr Boget has given the following expeditious method of deliaeat- ing a great number of magnetic curves, related to the same distance between two magnetic poles. He describes from each pole N. S., Fig. 66, as centres, the equal circles or semi-circles A. A., B. B., with as large a radius as the paper will allow ; and dividing the axis produced till it meets both circles, he marks off> on the circumference of both circles, the points where they are cut by perpendiculars flrom these points of division ; then drawing radii from the centre of each circle to the divisions of the respective circumferences, the mutual intersections of these radii will give different sets of points indicating the form of the magnetic curves which pass through them. Fig. 66, (Plate 11.) These curves are, in the present case composed, of a succession of diagonals of the lozenge-shaped interstices formed by the intersecting radii, as shown from converger.' curves in the upper half of the Figure. In the case of divergent curves, in Fig. 66, (PI. 11,) we must take the other diagonals of the lozenge-shaped intervals betwic :i the intersecting radii ; that is, the diagonals which cross those constituting the convergent curves. This is shown in the lower half of the Figure. ■« ' (' <;> ,, ,v^ ^ ../^ ■: ^ MAOXITIO CKAVSS. 17ft Plati 11. Ill $ ■ li MAGNETIO CUfiYES. , L'!<.i-y M. ■;'>■) ,iMr )' ■.:IJ4!-V: ;,; ,,:• i(-'.j .!. ^i"^.^•iy' J "^-i >^;;» 1^ lUaifXTIO OVKTIB. Sect. 11.— On themutual action ofMagwiU. , When a needle is exposed to the combined action of two magnetflt •8 shown in the annexed Fignre, the phenomena, though capable of calculation by the principles already explained, are extremely perplex- ing and complicated when studied experimentally. Tr. Bobison, who first discovered and explained these phenomena, has given such an interesting account of them, that we shall make use of his description of the phenomena, leaving the explanation of them to the next Motion on magaetio curves. llg. 46. " Two large and strong magnets, A. and B., were placed with their dissimilar poles fronting each other, and about three inches apart. A small needle, supported on a point, was placed between them at J>., and it arranged in the same manner as the great magnets. Happen- ing to set it off to a good distance on the table, as at ^., he was sur- prised to see it immediately turn round on its point, and arrange iteielf nearly in the opposite direction. Bringing it back to 2>., res- tored it to its former position. Carrying it gradually out aXongD.F., perpendicular to N.S., he observed it to become sensibly more feeble, vibrating more slowly ; and when in a certain point, E., it had no polarity whatever towards A. and B., but retained any position that XLEOTaiOAL INDUCTION 111 was given it. Carrying it farther out, it again acquired polarity to A. and B., but in the opposite direction ; for it now arranged itself in a position that was parellel to N. S. but <*'-' north pole was next to ^. and its south pole to /6^." • « • ; \ APPENDIX TO ELECTRICAL INDUCTIOH. (1734.) " Development of Electridiy by Induetion.—A conductor may be cliarged with electricity by an electrified body,though the latter shall not lose any of its own electricity or impart any to the conductor no electrified. For this purpose, let the conductor to be electrified be supported on a glass pilhir so as to insulate it, and let it then be connected with the ground by a metallic chain or wire. If it be desired to charge it with positive electricity, let a body strongly charged with negative electricity be brought close to it without touch- ing it. On the principle already explained, the negative electricity of tlie conductor will be repelled to the ground through the chain or wire; and the positive electricity will, on the other hand, be attracted from the ground to the conductor. Let the chain or wire be then removed, and, afterwards, let the electrified body by whose inductive action tlie effect is produced, be removed. The conductor will remain charged with positive electricity. It may in like manner be charged with negative electricity, by *he inductive action of a body charged with positive electricity."* * In this case the eondnctor connected with the ground and the grouna itself should be looked upon as one conductor, so long as they are connected. Therefore, removing the chain or wire cuts off the communica- tion between the one part of the conductor and the other. Rejecting the dual-hypothesia, the explanation will be that the body charged with negative electricity which ha? been deprived or denuded of its electricity attracts or inducps a quantity of electricity to that part of the conductor nearest to it. Tbe chain being removed and the inducing body being afterwards also removed, the electricity nceumulated in that part of the conductor (now insulated) is unable to return, and consequently remains in excess of the quantity which naturally or normally (so to speak) belongs to that part of the conductor. 378 ■I.MTRIOAL IM»VCT|ON. From Lardim't Natmml PMlotopkg. (1746.) "Bedproeal Induettve I^ffteU ^ two Oomd»don.—l( a conductor ul.,coniiMUDio«tii>g withtbt groand b* placed near anoUier conductor B. insulated ami charged with a certain quantity of cl«o- tricity E., a ueries of effects would cnsne by the reciprocnl inductive power of the two conductors, the result of which will be augmented in a certain proportion, depending on the distance between the two eondtictor8 through which the indoctive force aots." (1747.) " The electricity developed in such case^ on the conductor A. is subject to the anomalous condition o< being Incapable of passing; away though a coudnctor be applied to it. In (act, the conductor A. in the preceding experiment is 0uppo8e inductive action of A. is held thereby the influence of i4. and cannot escape even if the condnctors be applied in contact with it." (1748.) " Free Ehetrieity. — Electricity, therefore, wiiicb is deve- loped independently of induction, or which being first developed by induction, is afterwards liberated from the inductive action, is distin- guished as free electricity. In the process above descnbcd^ that part of the charge P. of the conductor B. which is expresecil by JET. and which was imparted to B. before the approaclt of the conductor.^., is free, and continues to be free after the approacli of A. Ifaconductoi- connected with the earth be brought into contact with ^., this elec- tricity E. will escape by it; bat all the remaining charge of B. will remain, so long as tlie conductor A. is auuntaincd in its position. If, however, E. be discharged from B. the charge whicli remains will not be capable of retaining in tlie dissiinulated state so- great a quan- tity of negative fluid on .^. as before. A part will be accoidingly act free, and if A. be maintained in connection with tlw ground it will escape. If ^ be insulated it will be charged with it still, but in a free state. If this free electricity be discbaurgied from A. the remaining charge will not be capable of retaining in the latent state so large a quantity of positive fluid on B. as previonsly, and a part of what was dissiniu- lateu will accordingly be set free, and nmy be discharged. ▼OLVMBTUO ILBOTRIOITT. 179 In thia manner, hj •Iternato diMhargiti from the one sod the other oonductor, the diaaimuUited charges may be gradually liberated and diamiaaed, without removing the oonductor iVom one another or aus* pending their inductive aot> *>». h iPPEVDIX TO TOLUUETRIO BLIOTRIOITT. From Fnme^ Manual of Chmittry. , , , " If glass, amber, or sealing-wax be rublioil with a dry cloth, it acquires the power of attracting light bodies, as feathers, dust or bits of paper i this is the result of a new and peouliar condition of the body rubbed, called electrical excitation. If a light downy feather be suspended by a thread of white silk, and 'V dry glass tube, excited by rubbing, be presented to it, the feather will be strongly attracted to the tube, adhere to its surface for a few seconds, and '.i en fall off. If the tube bo now excited anew, and presented to the (bather, the latter will be strongly repelled. The same experiment may be repeated with shellac or resin, the feather in its ordinary state will be drawn towards the excited body, and after touching, again driven from it with a certain degree of force. Now let the feather be brought in contact with the excited glass, so tis to be repelled by that substuiioc, and let a piece of excited sealing- wax be presented to it ; a degree of attraction will be observed far exceeding that exhibited when the feather is in its ordinary state. Or, again, let the fmtlior be made repulsive for sealing-wax, and then the excited glass presented ; strong attraction will ensue. The reader will at once see the perfect parallelism between the efi^ts described and some of the phenomena of magnetism; the electrical excitement having a two-fold nature, like the opposite polarities of the magi.et. A body to which one kind of excitement has been communicated is attracted by another body in the opposite state, and repelled by one in the state same. The excited glass and resin being to each other as the north and south poles of a pair of magnetized bars. To distinguish these two different forms of excitement, terms are employed, which, although originating in some measure in theoretical views of the nature of the electrical disturbance, may be understood by the student as purely arbitrary and distinctive: it is customary to oall the electricity manifested by glass pontive or vitreous, and that « i I . 180 TOLOlflTRIO ILIOTMOITT. developed in the oMe of ihellao, and bodies of tbe a»ine oltsf, negaiivt or ruinoui. The kind of electricity depends in some measure upon the nature of the surface t smooth glass rubbdd with silk or wool becomes ordinarily poiitive, but when ground or rough* enfd by sand or emery, it acquires, under the same circumstances, • negative charge. The repulsion shown by bodies in the same electrical state is taken nilvantage of to construct instruments for indicating electrical excite- ment and pointing out its kind. Two balls of alder-pith, hung by threads or very fine metal wires, serve this purpose in many cases | they open out when excited in virtue of their mutual repulsion, and show by the degree of divergence the extent to which the exoitemtnl has been carried. Fig. 66. Fig. 69. A pair of gold leaves suspended beneath a bell-jar, and communi* eating with a metal cap above, constitute a . uch more delicate arrangement, and one of great value in all electrical investigations. These instruments are called electroscopes or electrometers ; when excited by the communication of a known kind of electricity they show, by an increased or diminished divergence, the state of an electrified body brought into their neighbourhood. One kind of electricity can no more be developed without the other than one kind of magnetism t the rubber and the body rubbed always assume opposite states, and the positive condition on the surface of a massofmatter is invariably accompanied by a negative state in all surrounding bodies." The induction ./f magnetism in soft iron has its exact counterpart in electricity; a body already electrified disturbs or polarizes the particles of all surrounding substances in same manner and according to the same law, inducing a state opposite to its own in the nearer VOLCMITRXO IbSOTRIOlTT. m portion*, and a ■imilar state in the more remote parts. A sericH of globes BUHpended by sillc threadii, in the manner represented, will each become electric by induction when a charged body is brought near the end of the series, like so many pieces of iron in the vicinity of a magnet, the positive half of each globe looking in oneand the sam* direction, and the negative half in the opposite one. The positive •nd negative signs aip intended to represent the statM. -4[^^-(|^-y Pig. 60. The intensity of the induced electrical disturbances diminishes with the distance from the charged body i if this be removed or discharged, all the effects cease at once. So far, the greatest resemblace may be traced between inese two sets of phenomena ; but here it seems in a great measure to cease. The magnetic polarity of a piece of steel can awaken polarity in a second piece in contact with it by the act of induction, and in so doing loses nothing whatever of its power; this is an effect completely different from the apparent transfer or discharge of electricity con* ■tantly witnessed, which in the air and in liquids oflen gives rise to the appearance of a bright spark of fire. Indeed, ordinary magnetic efibcts comprise two groups of phenomena only, those namely of attraction and repulsion, and those of induction. But in electricity, in addition to phenomena very closely resembling these, we have the effects of discharge, to which there is nothing analogous in magne- tism,* and which takes place in an instant when any electrified l)od7 is put in communication with the earth by anyone of the class of substances called conductors of electricity ; all signs of electrical disturbance then ceasing. * May not the magneto-olectric machine (page 168), wherein the poles of the armature in wbicb the magnetism i': induced, are suddenly and continually reversed in front of the magnet, be considered as exhibiting a succession of discharges (of molecular or magnetic electricity) 7 The wire, in that case, which is coiled an immense number of times around the magnet, would represent, or be analogous to, the condenser and conductor of the volnmetrio electricity. 182 fOtOillBTRIO tShUmVLtClTt. These conductors of electricity, which thus permit dldcharii^B td take place through their mass, are contrasted with another class of substances called non-conductors or insulators. The difference, however, is only one of degree, not of kind ; the very best conductors oBet a certain resistance to the electrical discharge, and the most perfect insulators pennit it to a small extent. The metals are by far the best conductors ; glass, silk, shellac, and dry gas, or vapour of any sort, the very worst ; and between these there arc bodies of all degrees of conducting power. Electrical discharges take place silently and without disturbance in good conductors of sufficient size. But if the charge be very intense, and the conductors rery small or imperfect, from its nature, it is often destroyed with violence. When a break is made in a conductor employed in effecting the discharge of a highly excited body, disruptive or spark-discharges, BO well known, take place across the intervening air, provided the ends of the conductors be not too distant. The electrical spark itself presents many points of interest in the modifications to which it is liable. The time of transit of the electrical wave through a chain of good' conducting bodies of great length is so minute as to be altogetheF inappreciable to ordinary means of observation. Professor Wheats stone's very ingenious experiments on the subject give, m the instanott of motion through • copper wire, arekjoity approaching that of lights Electrical excitation is appareHt only upon the surfaces of bodies^ or those portions directed towards other objects capable of assuming the ociXMite state. An insulated ball charged with positive ele<^'' city, and placed in the centre of 'he room, is maintained in that stats by the inductive action of the walls of the apartment, which immfr* diately become negatively electrified ; in the interior of the ball then is absolutely no electricity to be found, although it may be con- structed of opm mfttal gauM, with meshes half an inch wide. Even on the surface the distribution of electrical force will not always be the same it will depend upon the figure of the body itself, and its position with regard to surrounding objects. Tht; polarity will always be highest in the projecting extremities of the same conduct- ing mass, and greatest of all when these aire attenuated to points, in which case the inequality becomes so great thai discharge takes place to the air, and the excited condition cannot be maintained. VOXmOfeTBIT SLEOTRIOrrt. T1IB ELEOTBIOAL MAOHINE AND OONDKNSBR. 18^ The ordinary plate machine, Fig. 62, is thus described by Fownea : *' Another fonn of the electrical machine eonsiBts of a circular plate of glass moving upon an axis, and provided with two paira of cushions or rubbers, attached to the upper and l«.7er parts of the wooden frame, covered with amalgam, between which the plate moves with considerabls friction. An insulated conductor, armed as before with points, discharges the plate as it turns, the rubbers being at the same time connected with the ground by the woodwork of the machine, or by a strip of metal ." Fig. 62. The most simple modification of the electrical machine is the elec- trophorus already mentioned (page 180); another form of the elec- trophorue is shown at Fig. 11, contrived by Mr. John Ph.lhps.of York, in which the resinous disc is perforated and brass wires c. c. c. in the Fig.) are inserted through the bottom plate and have their ends level with the surface of the resin, so that when the cover is put on, communication be- tween it and the ground is establiahed through the wires. " With ordinary ex- 184 YOLUIIBTBIO KUEOTUOITT. citation this instrument will yield loud flashing sparks two inches long or more, and speedily charge cpnsiderable jars. The cover can be easily charged and discharged fifty or a hundred times in a minute, by merely setting it down and lifting it up as fkst as the operator chooses, or the hand can work. In charging a jar or plate, I place one knob oi the connecting rod near the insulated surface of the jar or plate, and the other some inches above the cover { then the cover being alternately lifted up and set down* the jar ifl rery quickly charged." - THE CONDENSER AND LETDEN JAB. From Lu, diUf*M Aahtni FhUoaophy., (17S9.) '* The mauctive prmcip.e wnich has supplieu the meanfl in the case of the condenser of detecting and examining quantities of electricity so minute and so feeble as to escape all common tests, has placed in the Leyden jar, an instrument at the disposal of the electri- cian, by which artificial electricity may be accumulated in quantities so unlimited as to enable him to copy in some of its most conspicuous effects the lightning of the clouds. To understand the principle of the Leyden jar, which at one time excited the astonishment of all Europe, it is only necuasary to inves- tigate the effect of a condenser of considerable magnitude placed in connection, not with feeble but with energetic sources of electricity, such as the prime conductor of an electrical machine. In such case it, would be evidently necessary that the collecting and condensing plates should be separated by a non-conducting medium of sufficient resistance to prevent the union of the powerAil charges with which they would be invested. Let A. B., Fig. 499, represent the collecting plate of such a condenser, connected by a chain K. with the conduc- tor E. of an electric machine; and let A'. B. be the condensing plate connected by a chain K. with the ground. Let (7. i>. be a plate of glass interoosed between A.B, and A B. VOhVUMTWS XLIOXUCITT. 195 1' ta>^^ w^ Let «. express the quantity of eleetrioUj with which a superfloial unit of the oonductor E. is charged. It follows that t. will also express the free electricity on every super- ficial unit of the collecting plate A. B., and of the total charge on each superficial unit of ii. B. free and dissimulated, be expressed by n., we shall, according to what has been already explained, have. a =- 1 — »» " When the machine has been worked unUl e. ceases to increase, the charge of the plates will have attained its maximum. Ijet the chains K. and K be then removed, so that the plates A. B. and A'.B'. shall be insulated, being charged with the quantities of electri- city of contrary names expressed by E. and E.'" " In order to divest these principles of whatever is adventitious, and to bring their general character more clearly into view, we have here presented them in a form somewhat difibrent firom that in which they sre commonly exhibited in electrical experiments. The phenomendn which has just been explained, consisting merely in the communication of powerful charges of electricity of contrary kinds, on the opposite foeea of glass or other non-conductor, by means of metal maintained in contact with the glass, it is evident that the form of the glass and of the metal in contact with it, have no influence on the effects. Neither has the thickness or volume of the metal any relation to the results. Thus the glass, whose opposite fa^es are charged, may have the form of a hollow cylinder or q>here, or of a common flask or bottle^ and the metal in contact with it need not be masmve or solid plates, but merely a coating of metallic foil. H 186 VOLXniXTRIO ILIOTRIOIXT. ' 1760. The Leyckn Jar.— In experimental researches, therefore, the form which is commonly given to the glass, with a view to develop the effects, is that of a cylinder or jar A. B., Fig. 600, having a wide mouth and aflat bottom. The shaded part terminating at 0. is a coating of tinfoil placed on the bottom and sides of the jar, a simijar coaling being attached to the cor> responding part of the interior surface. A metallic rod, terminating in a ball 2>., descends into the jar, and is jomed (?) in contact with the inner coating." (The flattened base of the rod rests upon the inner coating at the bottom of the jar.) 1763. " Experimental proof that the charge adheres to the gUuatmd not to the coating. — The electricity with which the jar is charged in this case resides, therefore, on the glass, or on the conductor by which it passes to the glass, or is shared by these. To determine where it resides, it is only necessary to provide means of separating the jar from the coating after it has been charg^, and cxamiaing the electrical state of the one and the other. For this pur- pose let a glass jar be provided, having a loose cylinder of metK.1 fitted to its interior, which can be placed on it or withdrawn from it at plea- fiure, and a similar loose cylinder fitted to its exterior. The jar being placed on the external cylinder, and the internal cylinder being inserted in it, let it be charged with electricity by the machine in the manner already described. Let ths internal cylinder be then removed, and let . the jar be raised out of the external cylinder. The two cylinders being then tested by an electroscopic apparatus, will be found in their natural state. But if an electroscope be brought within the influence of the internal or external surface of the glass jar, it will betray the presence of the one or the other species of electricity. If the glass jar be then inserted in another metallic cylinder made to fit it externally and a similar metallic cylinder made to fit it internally be inserted in it, it will be found to be charged as if no change had taken place. On connecting by metallic communication the interior with the cx> terior, the opposite electricities will rush towards each other and com- bine. It is evident, therefore, that the seat of the electricity, when a jar is charged, is not the metallic coating, but the surface of the glass under it." VOLTJMKtRIO ILXOTRIOITr. 187 We do not find any record of this very interesting and instructive experiment having been further pursued. The •conclusion here stated does not appear to be demonstrated 'by the evidence, and it must, for the present at least, be considered questionable and possibly deceptive. By thus igradually withdrawing one metallic cylinder at a time, the effect would be to transfer the electricity to the glass •vessel by distributing it evenly over the surface thereof. For the purpose of obtaining more decisive evidence the experiment may be thus followed: — (Fig. 601.) Let two loose cylinders of glass, open at both ends, represented at g. 1 and 2, in the figure, be placed upright, one inside 4"»» JFig. 601. ^ the other, upon a plate of glass P.; and let two cylinders 'Of metal, I. and 0., not so long as the glass cylinders, be also placed upright on the glass plate, one of them, marked I. in the fig.^ inside the smaller gl -lSS cylinder, and the ^i' II 188 yOLimTBIO BUOTBIOITT. other (metal cylinder), marked 0., outside the larger glass cylinder. The apparatus being thus arranged, let either one of the metal cylinders be made to connect with the earth by a conducting chain attached to it, or in some other suitable manner, and let the other metal cylinder be then charged with electricity ; after which, the chain or other connector may be detached. Either one of the glass- cylinders may be now removed and tested by the electro- scope. If it be found not to have brought with it any of the electricity, it may be replaced and the other glas» cylinder may be removed and tested. Should it fur-^ ther ' pear that the second cylinder had likewise brought away none of the electricity, the first glass cylinder may be then also removed. If the distance between the two metal cylinders is but small and the charge considerable^ the electricity will now pass through the air from the- one to the other, and they will be thus discharged, but, on the one hanch, the distance between the cylinders may be increased, or, the quantity of electricity supplied to the apparatus may be lessened, because a very slight charge would suifice to try the question.* On the sup> position that the actual result baa not been as yet experimentally ascertained, we opipe that the electricity (all of it) will be found, contrary to Dr. Lar^r's con- clusion, to remain with the metal cylinders. • It IB here intended for the flinders to be close together and their gidei to be almost in eontact, bot, we would suggest that, by taking flin- ders difftring considerably in site, so as to increase the distance between them, some other interesting questions might be in this way submitted to experiment The matnial of which the cylinders an composed might b» alsoTaried. ' , l^> yOLtrmcuo iLiotaioiTT. Id9 Lard/net's Natural Phihsqphy. (17M.) " Charging a amiu t^ ^ surface of the next jar, and yet the supposed two eleC' tricities, having such a powerful attraction each for the other, remain separate and distinct ! For example, if we suppose the outside charge of the jar marked A. 1, to be negative electricity, then, by the record, the inside charge of the jar A. 2, is positive electricity, and between these, communicating with both of them, there is the conducting chain C. The argument may su^'^gest itself as a reply . . . Oh, a» to that, . . if you suppose only one kind of electricity you are in precisely the same difficulty. But it is not so ; . . electricity is communicated, we will suppose, to the interior coating of jar A 1, this having distributed itself over that interior surface acts by induction on the exte- rior surface, driving out the electricity over the conduct- ing chain into the interior of the next jar, where it dis- tributes itself and acts inductively on the surface of th& exterior coating of that jar, as before, and so on. Now this is quite intelligible, because the fact has been esta- bUshed by observation of many other distinct cases thak electricity has precisely such inductive action, and th& same influence of the free electricity on the one surface which drives out the electricity from the other surface, will evidently, being still free and active, prevent its return, (and this applies to the case of each jar.) It is true that no theoretical reason, based on other and disf- HOLSOULAB BLICTRIOITT. 191 tinct facts can be at present shown why electricity should thus act inductively, it is an observed property or in- fluence belonging to that particular force, and which being known the explanation of the result is quite intel- ligible. We would remark, in conclusion, that this case, also, does not appear to have received that share of at- tention, from experimental investigators, which the very interesting and peculiar nature (so to speak) of the phen- omenon invites and calls for. V MOLECULAR ELECTRICITY. ' The Encyclopedia Bniannica. ■ ■. Voltaic Electricity. Sec. IV, On the production -of Light, Heat and Cold by Voltaic Electricity. — The Ignition of Wires. — " It was \a England, however, that the calorific and luminous effects of the pile were principally developed. In 18L3, the immense battery of the Royal Institution, composed of 2000 couples, and exposing 28,000 square inches, enabled Sir H. Davy to produce light and heat of the highest intensity. When the ends of the wire from each pile terminated id two charcoal points, the most dazzling light passed from the one to the other, and continued for several hours. Steel wires and thin leaves of different metals, were made red hot and burned, and water was boiled by plunging into it an iron wire two feet long and the one-hundredth of an inch in diameter, and placed between the poles of the battery. Platina, sapphire, quartz, lime, ko., when exposed to this source of heat, were instantly melted, and the diamond and charcoal disappeared as if they were completely volati- lized. These effects were produced in vacuo as well as in air." " At the same time that Mr. Children was constructing the greatest voltaic battery ever made, Dr. Wollaston was occupied in constructing the smallest. He took a small thimble, as we have already stated, and having removed the bottom, he flattened the remaining cylinder till its sides -were about one-sixth of an inch distant. He then placed between these two surfaces a small plate of zinc which did not touch . either side of the thimble. With a platinum wire about one-fortieth I m MOLlOtTLAK ILIOTBXOITT. offtn i&oh long, and one-three thouMndth of m inoh in diameter, he united eztemallj the plate of line, with this thimble i and when thia little galvanic couple was immersed in acidulated water, the platinum wire became red hot, and was melted I This important result led Dr. Wollaston to the valuable conclusion, that in order to obtain power- ftil calorific effects, we must increase the surfkce of the copper or negative metal." " In repeating the experiments of Davy on the light developed by charcoal points, Mr. Brandes discovered that this light, like that of the sun, affected the combination of chlorine and hydrogen, and the decomposition of muriate of silver and other bodies. "By means of the powerAil voltaic battery which Dr. Hare calls a deftagrator, and which we have already described, this able chemist obtained some splendid results. A brilliant light, equal to that of the sun, was produced between charcoal points ; and plumbago and char- coal were fused * by Professors Silliman and Oriscom. By a series of 260, baryta was deflagrated { and a platinum wire, three-sixteenths of an inch in thickness, * was made to flow like water.' In the experi- ments with charcoal, the charcoal on the copper side had no appear- ance of fusion, but a crater-shaped cavity was formed within it, indi- cating that the charcoal was volatilized at this side, and transferred to the other, where it was condensed and fused, the piece of charcoal at this pile being elongated considerably. This fused charcoal was four times denser than before Aision. <* Owing to its superior conducting power, a continued voltaic our. rent will maintain in a state of incandescence a greater length of silver wire than of platinum or iron ; but if we form a wire of short pieces of Silvelr and platinum wire alternately, the platinum portion will be- come red hot, while the silver ones remain cold. In this case, the current which passes readily along the silver wire, encounters the de- gree of obstruction in the platinum which produces the red heat. The fiust is no doubt connected with the very remarkable one observed by M. Peltier, in the passage of weak currents through metallic circuits, * This Alston of charcoal and plumbago has not been, we believe, by any meaas demonstrated. The volatilisation of those forms of carbon may be also considered suppositious; conolusive evidence is wanting; these experiments show merely that a superficial disintegration and a partial modification of the solid is efiiected, and that some of the particles separated by the electric force are transferred from the one electrode to the other. MOLBOULlft BLIOTRIOITT. 193 when cold wm produced at the point* of junction of oerUinorystallif • «ble metftls." ■ (( Liqaidfl, Ilk* solids, which are the worst conductors, are the most heated by electrical currents, a result arising (h>m the resistance which the current experiences." * " While in static electricity, we have the interesting phenomenon of the electrie tpark, already discussed in the article 'Electricity.' We have in voltaic electricity the no less interesting phenomenon of the a h Fig. 66. voltaic arch, which was discovered by Oavy. It is represented at a. b. in the annexed figure, as produced between two charcoal points 4 inches distant, transmitting a current from 2000 pairs of zinc and copper, having each a surface of 32 square inches charged with acidu- lated water. It has the form of an arc convex above, and when the most reflraotory substances' were placed in it, they became incandes- cent, and disappeared as if by evaporation. When one of the points a. was charcoal and the other 6. plumbago, the particles of charcoal were transftrred in the state of vapour to the plumbago, ftom the positive to the negative pole, and by interchanging the poles the plumbago was transported to the positive pole, as first shown by Dr. Hare. The appearance and length of the arc varies with the nature of the electrodes or points a. b. between which it appears. Mr. Orove found that the longest and most brilliant arc, when shown in air, was produced when the electrodes were potassium, sodium, einc, mercury, Iron, tin, lead, antimony, bismuth, copper, silver, gold and platinum, the first giving the largest and brightest arc, and the rest * This conclusion may be considered hypoth$tieal . . .i.e., an opinion based on hypothent ; » . . it would be better to say ' a result which appears to be connected with a resistance experienced by the supposed current.' 194 MOLKOULAR ILROTftlOITT. as in their order. Mr. Orove also observed, that in vaouo the trans- ported matter was in the state or inetnilio powder when the medium vas hydrogen, nitrogen or a vacuum, and an oxide in air or in oxy- gen." Sect. V. On the Chemical Effeett of VoUaic EUetridty. "No sooner was this apparatus made known in England, than Messrs. Nicholson and Carlisle applied it to chemical enquiries. Although Volta had inferred fVom the shock that the action of the pile was electrical, yet it was to the above enquirers that we are indebted for determining, by means of the revolving doubler, that the silver end of the buttery was in a negative and the tine end in a positive state of electricity. In the course of their experiments, they observed a disengagement of gas which smelt of hydrogen, fVom water which happened to be in the circuit ; and on the 2nd of May, 1800, they discovered that water was decomposed into its elements, viz., oxygen and hydrogen, when the water foraied part of circuit between the posi- tive and negative ends of the pile." • • • • " The attention of our illustrious countryman, Sir H. Davy, was about this time attracted to the subject. So early as 1802, he had made experiments on the chemical agency of the pile ; but in 1806, in his first Bakeriau Lecture, he was led to the conclusion, that chemical attraction and repulsion werr vroduced by the same cause, acting in tke one case on particles, in tl.a other on masses, and thai the same pro- perty, under d^erent circunutances,v}as the cause of all the phenomena exhibited by different voltaic conUnnations." " With a voltaic battery of 200 plates, he decomposed several of the earths, and discovered their metallic bases, barium, strontium, calcium and magnesium." "In revolving a compound body into its elements, liquidity is an essential condition of the body. A plate of iron, the sixteenth of an inch thick, placed between the two sides of the pile, will stop com- pletely the most powerful electrical current." " By an irresistible body of evidence. Dr. Faraday has established the important proposition, ' that the chemical power of a current of electriciiy ia in direct proportion to the absolute quantity which passes ; and this is true of all bodies capable of electro-chemical de- composition. The same eminent philosopher has also deduced^ ih>m a variety of facts, the following conclusion : < that the quantity of electricity, which, being naturally associated with the particles of ACOUSTIC rOROB AND BLICTRIOITT. 19ft matter, givei them their combining power, ia able, when thrown into » current, to separate theie partiolei flrom their etate of combination » or, in other wordi, that th« eketrieHy whioh dteompotet and that which it evolved 6y the deeompoiition <\f a eertain quantity of matter are alike.' According to thifl theory, < the equivalent weighto of bodies are eimply those quantities of them which conUin equal quantities of electricity, or have naturally equal electric powers, it being the electricity which determines the equivalent number, because it de- termines the combining force i or, if we adopt the atomic theory or phraseology, then the atoms of bodies which are equivalents to each other in their ordinary chemical action, have equal quantities of elec- tricity naturally associated with them." ACOUSTIC FORCE (SOUND) AND ELECTRICITY. Encyclopedia Britannica, on the vibratory movements and sounds produced by the Electric Currents.— 80 early as 1786, the Canon Got- toin, of Como, a iViend of Volta's, observed that an iron wire, 30 feet long, when stretched in the open air, emitted a sound in certain stales of the atmosphere. Page, Delezenne, Oassiot, and Marienini, observed sounds from electric currents under different ciroumstancea ; but it ier to Delarive that we owe the most interesting experiments on the sub- ject. When a magnetic but unmagnetized body, such as iron or steel, is placed in the interior of a bobbin, very remarkable rotary move- ments are produced by discontinuous currents passing through the wire which encircles the bobbin . Two sounds are always distinguished, one a series of blows or shocks, like the noise of rain falling on a metal roof, and the other musical. A mass of iron four mches in diameter, and weighing 22 lbs., placed within a large tube, gave out a very clear and brilliant musical sound ; but the most brilliant of all are those obtained by stretching on a sounding-board well-annealed wires from three to six feet long, and one-fiileenth of an mch in dia- meter." "A remarkable vibratory motion produced by electricity was obeerred by Mr. Fearn, of Birmingham, in his electro-gilding estab- lishment When a brass tube 4 feet long and | inch wide in diameter was placed upon, and at right angles to, two horizontal and parallel brass tubes 9 feet long and an inch in diameter, and the latter con- nected with a strong voltaic battery of from two to twenty pair of 196 A00U8TI0 rOBOX AND ELIOTBIOITT. large cino »nd carbon eletnenta, the tranaverse tube immediately began to vibrate, and finally to roll upon the other two. Mr. O. Gore, who repeated the experiment under various circum* stances, found that when the resistance was small and uniform, the rolling tube continued to move in the same direction imparted to it ; but that when the resistances were not uniform, it continued to roll backwards and forwards as long as the electric current was passing. Pig. 67. In order to obtain a continuous rolling motion, Mr . Gore constructed the apparatus, where ^. is a circular base of wood provided with two loose rails or hoops, B. and C. about one thirtyflfth of an inch thick, the outer one being one-fourth of an inch higher than the other, &nd both being uniform and equidistant. F. is a perfectly round thin «opper ball, hollow and equally thick, weighing about 600 grains. When the circular base.^. E. is made level, the ball F- placed upon the rails, and a voltaic cunreiit, copious in quantity and moderate in intensity, intrcduced at the screws D. and E., the ball will begin immo- 'diately to vibKNte, and increase its motions till it revolves upon the rails. It revolves with equal facility in either direction as long as the current is passing, and it becomes much heated during its motion. With three sine and carbon batteries, the einc cylm^ a glass vessel containing mercury, and hav ing a small cylindrical magnet F. fixed to its bottom, aud projecting a little above the surface of the mercury. The wire d, being attached by a hook to the horizontal arm C. will commence its revolutions round as soon as the voltaic current passes in the direction of the ■arrows, or x. JP. d. C. If we make the current pass in the direc- tion a. d. e. C. F. x. from the zinc to the platinum end of the battery, both the above revolutions will go on simultaneously. Whep the cur- rent was made to pass in the opposite direction, the direction of the rotation was likewise changed. " The rotation of liquid conductors may likewise, as Sir H. Davy has shown, be produced by the pole of a magnet. If mercury is placed in a shallow dish between the two poles of a battery, a magnet placed either above or below the mercury, will cause the mercury to revolve round the points from which the currents issue. The rotation of the flame produced by the passage of a powerful voltaic charge between two charcoal points, arises from the same cause. Prof. Daniell gives the following pleasing method of showing the efiect. He makes a powerful horseshoe magnet part of the conducting wire of a constant battery of a moderate number of cells ; the flame which may then be drawn from one of its poles will revolve in one direction while that from the other will revolve in the opposite direction." " Various forms have been given to these electrodynamic cylinders. In some the coils all lie in one plane, as in Pig. 71,' where one face of the coil has north, and the other south polarity, the magnetic poles being as it were situated in the centre of each disc. Fig. 72. When the helix is constructed, as in Fig. 72, its power is so great that a small steel bar S. N. placed within it, and supported perpendi- oularly, will, as soon as the connection is made with the voltaic battery, by means of the mercury cap, P. p, start up, and place itself * See page 220. 200 KOTATOKT IfFXOTS OF HAGNBTISM. ROTATORT EFFECTS OF HAQNETIBM. 201 " in the air, where, like Mahomet's cofBn, it will remain suspended without any visible cause, and in opposition to the power of gravitation. We owe also to M. Ampere the very interesting apparatus of a small voltaic battery made to revolve round a magnet. This is shown in Fig. 73, where A. B. C. D. a.b.e.d. exhibits a section of two cylinders of copper soldered to a copper bottom, so as to hold a fluid. The double cylindrical vessel is suspended by a bent wire a. F. b. (having a cavity at F.,) upon the north pole N. of a vertical magnet N. S. A. lightcylinder of zinc z. z. is also so suspended by a bent wire z. E. z. and a steel pivot at E. upon the same pole N: of the magnet. The cylinder z. z. can therefore revolve upon this pivot. When the cylinder A. B. D. d. b. a. c. C. A. is filled with dilute acid so as to constitute a small battery, the cylmder z. z. will revolve from left to right when N. is the north end or south pole, and from right to left when N. is the south end or north pole. Owing to the attraction of the fluid, the cylinder of zinc is often drawn to one side, and prevented from moving ; but this may be avoided by making the space A. e. Bufliciently wide. Mr. Watkins has ingeniously applied this contrivance to the poles of a horse-shoe magnet, as in Fig. 74.* It consists of a horse- shoe magnet A. B. fixed to a stand S. S. Above each pole is sus- pended a double cylindrical copper vessel, with a bent metallic wire fixed to the top of the inner cylinder, and a vertical wire, pointed at each extremity, fixed in the middle of the bent wire. The lower ends of the vertical wires of each cylinder refit in the holes of each pole of the magnet. Within the above double copper vessel are placed two hollow cylinders of zinc, having] similar bent wires with holes in the lower side of each, in which holes, the upper ends of the vertical wires are inserted. When the copper cylinder is filled with dilute acid, the voltaic action begins, all the four cylinders revolving round their respective axes. The copper cylinders turn slowly and heavily from their weight, in opposite directions to one another and the zinc cylinders, with great velocity, in opposite directions to the copper ones. * See page 200. Fig. 73. 202 BOTATORT EFFECTS OF HAONKTI8M. Very delicate suspensions are necessary to ensure the rotation of the copper cylinders. "A very simple apparatus for shewing the magnetic stateof a single coil is shown in Fjg. 75, where Z. and C represent the elements of a omall galvanic battery of one zinc and one copper plate attached to a cork vhich floats on dilute acid. Each plate is half an inch wide, and two inches long. A piece of copper wire W. with silk thread wrapped round it, is bent into a ring, one end of which is soldered to the zinc, and the other to the copper plate. Fig. 75. Fig. 7C^. An electric current now passes in the direction of the arrow, and the ring W. becomes a flat magnet, having its poles in the centre of its two surfaces, the one being north and the other south. This floa- ting magnet will, when acted upon by a real magnet, exhibit the usual magnetic attractions and repulsions. Mr. March has improved this apparatus by doubling the copper plate as in Fig. 76, and conver- ting it into a vessel for holding the dilute acid. The plates are then placed in a glass cylinder which may float in water." The magneto-electric machine has been greatly improved by Mr. E. M. Clarke, magnetical instrument maker, London, f It is repre- in Fig. 94, where A. is the battery of bent bar magnets resting against the vertical board B., and by means of a bar of brass C, * ." A very beautiful apparatus for exhibiting helical rotation has been constructed by Mr. Watkins, and is shown in Fig. 77." It ia thought that the figure will for the present purpose sufficiently explain itself as a modi- fication of those preceding it. t This improved form of the M, E. machine may be compared with that already illustrated at page 168 from Fownea' Manual of Ghemistry. The illustration is repeated on the same plate at Fig. 96. ROTATORY EFFE0T8 OF MAGNETISM. 203 Fig. 95. Fig. 96. 204 MAaNlTO-BLECTRICITT. " with a bolt and screw-wheel, the magnets can be drawn firmly to the board B. or taken from it. One of the keepers or armatures D. is screwed into a brass mandrill between the poles of the magnets, and it is made to revolve by the multiplying wheel E. This armature has two coils of fine copper wire, 1500 yards long, wrapped round its cylinders, the beginning of each coil being soldered to the armature D. from which also projects a brass stem carrying the break-piece If., which can be fastened in any required position by a binding screw ; a hollow brass cylinder K., to which the ends of the coils are soldered, being insulated by means of a piece of hard wood attached to the brass stem. An iron wire spring 0. passes at one end against the cylinder K., and is kept in contact with it by a screw in a brass strap M. in the wooden block L. A square brass pillar P. fits also a square opening in the other brass strap N., on the other side of the block L. A metallic spring Q. rubs gently upon the break piece H., and is retained in perfect metallic contact with it by a screw in the pillar P , the two straps of brass M. N. are connected by a piece of copper wire T., and in this state the parts D, H. Q. P. N. are in con- nection with the commencement of each coil, und the parts K. 0. M. with the termination of each coil. The perfect metallic contact thus obtained by the spring and break, enables Mr. Clarke to dispense entirely with the use of mercury, which is at all times a troublesome accompaniment of machinery. " But the great superiority of Mr. Clarke's machine arises from his employing two diflTerent armatures, and thus being enabled to produce the separate effects of quantity and intiensity to the full extent of the power of his battery. Having, in November, 1834, tried .the efifects of coils of wire of difierent thickness, he found that the thick copper bell wire gave brilliant sparks, but no perceptible shock, while very fine wire gave powerful shocks, but very feeble sparks. By means of the intensily armature, which is that shown in Fig. 94 the various experimenta made with a number of separate galvanic plates may be performed, while the intense agony produced by its shocks is intolerable: it can, at the same time, (7) electrify the most nervous person without occasioning the least uneasiness. It decom- poses water and the neutral salts. It deflects the gold leaves of the electroscope, charges the Leyden jar ; and by an arrangement of wires from the mercury box to the battery, the electricity is made visible. MAONITO-SLSOTRIO FOROB. 205 " paseing from the magnetic battery to the armature, and sparks and brilliant scintillations of steel can be obtained. The quantity armature difTers greatly from the intensity one, as shown in Fig. 96, which exhibits the method of producing the spark. The weight of the iron in the cylinders is much greater than in the intensity one, the copper wire is much thicker, and its length is only forty yards. By this armature all the experiments can be made which are usually performed by a single pair of voltaic plates of large sur- face, or by a calorimotor ; but it will not do for any of the intensity experiments. It produces such large and brilliant sparks, that a person can read small print from the light it produces. It ignites gunpowder and platinum wire, without enclosing the. wire in a her- metically sealed glass case. It deflagrates gold and silver leaf, and produces brilliant scintillations from a small steel file. It produces also rotatory motions in delicately suspended wire frames round the poles of a vertical horseshoe magnet and all the other effects of voltaic electricity . - . Although the law which go^'ern8 the evolution of electricity by magneto-electric-induction is very simple, yet Dr. Faraday has found it rather difficult to express it, except in reference to diagrams. We shall therefore give it ir his own words : " If in Fig. 89, P. K. re- present a horizontal wire passing by a marked magnetic pole so that the direction of its motions shall coincide with the curved line proceedir.g fro»r be'nw upwanls ; or if its motion parallel to itself be in a line tangential to the curved line, but in the general direction of the arrows ; or if it pass the pole in other directions, but so as to cut the magnetic curves * in the same general direction, or on the same side as they would bo cut by the wire, if moving along the dotted curved line; then the current of electricity in the wire is from P. to N. If it be carried in the reverse direction, the electric current will be from N. to P. Or if the wire be in the vertical position, as at P.' N.', and Fig. 89. * " By magnetic carves, I mean the lines of magnetic force, however modified by the juxtaposition of poles, which would be depicted by iron filings, or those to which a very small magnetic needle would form a tan- gent." 206 MAQNBTIO-XLIOTaiO FORCC. " it be carried in eimilar directions, coinciding with the dotted horizon* tal curve, so far as to cut the magnetic curves on the same side with it, the current will be from P.' to JV. If the wire be considered a tangent to the curved surface of the cylindrical magnet, and it be carried round that surface into any other position, or if the magnet itself be revolved on its axis, so as to brirg any part opposite to the tangential wire ; still, if afterwards the wire be moved in the directions indicated, the current of electricity will be from P. to N. ; or if it be moved in the opposite direction, from N. to P. ; so that as regards the motions of the wire past the pole, they may be reduced to two, directly opposite to each other, one of which prodtices a current from P. to N. and the other from N. to P. The same holds true of the unmarked pole of the magnet, except that if it be substituted for the one in the figure, then, as the wires are moved in the direction of the arrows, the current of electricity would be from N. to P., and when they move in the reverse direction from P. to JV. " Hence the current of electricity which is excited in metal when moving in the neighbourhood of a magnet, depends for its direction altogether upon the relation of the metal to the resultant of magnetic action, or to the magnetic curves, and may be expressed in a popular way, thus : Let A. B. (Fig. 90) represent a cylinder magnet, A. being the marked pole, and B. the unmarked pole ; let P. N. be a silver knife blade resting across the magnet, with its edge upward, and with its marked or notched side to- wards the pole A.; then in whatever direction or position this knife be moved edge foremost either about the marked or the unmarked pole, the current of electricity produced will be from P. to N. provided the intersected curves pro- ceeding from A. abut upon the notched surface of the knife, and those from B. upon the unnotched side. Or, if the knife be moved with its back foremost, the current will be from N. to P. in every possible position and direction, provided the intersected curves abut on the same surfaces as before. A little model is easily constructed, by using a cylinder of wood for a magnet, a flat piece for the blade, and a piece of thread connecting one end of the cylinder wiih the other, and MAONITO-lLBOTaiO FOROI. SOT " pasiiing though a hole in the blade for the magnetic curven t this readily giveB the result of any poasible direction/ When the wire under inducation is passing by an electro-magnetic pole, as, for instance, one end of a copper helix traversed by the electric current, the direction of the current in the approaching wire is the same as that of the current in the parts or side of the spirals nearest to it, and in the receding wire the reverse of that in the parts nearest to it. All these results show that the power of inducing electric currents is circumferentially exerted by a magnetic resultant, or axis of power, just as circumferential magnetism is dependent on, and is exhibited by, an electric current." (Note.*) — ^The following clearly expressed statement from Fowne^s Manual of Chemistry, may enable (or assist) the reader to correctly appreciate the preceding expla- nation. " The action which a current of electricity, from whatever source proceeding, exerts upon a magnetized needle, is quite peculiar. The poles or centres of magnetic force are neither attracted nor repelled by the wire carrying the current, but made to move around the latter, by a force which may be termed tangential, and which is exerted in a direction perpendicular at once to that of the current, and to the line joining the pole and the wire. Both poles of the magnet being thus acted upon at the same time, and in contrary directions, the needle is forced to arrange itself across the current, so that its axis, or the line joining the poles, may be perpendicular to the wire ; and this is always the position which the needle will assume when the influence of terrestrial magnetism is in any way removed. This curious angu- lar motion may even be shown by suspending a ipagnet in such a way that one only of its poles shall be subjected to the current ; a permanent movement of rotation will continue as long as the current is kept up, its direction being changed by altering the pole, oi' revers- ing thecurrent. The moveable connections are made by mercury, into which the points of the conducting wires dip. It is often of great practical consequence to be able to predict the direction in which a particular pole shall move by a given current, because in all galvan- OBCopes, and other instruments involving these principles, the move- ment of the needle is taken as an indication of the direction of the cir- 208 MAONKTO-BLIOTBIO FOROB. " culating current. And this ia euily done by a simple meohanioal aid to the memory. Let the current be supposed to pass through a watch iVoni the face to the back ; the motion of the north pole will be in tho direction of the hands, or a little piece of apparatus may be used if reference is often required ; this is a piece of pasteboard, or i ^ [fc ; '"*\M i Fig. 68. other suitable material, cut into the form of an arrow for indicating the current crossed by a magnet having its poles marked, and ar- ranged in the true position with respect to the current. The direction of the latter in the wire of the galvanoscope can at once be known by placing the representative magnet in the direction assumed by the needle itself." On th« AppUcationt of EUctro-Magnetiam. Encyclopedia Britannica. — " The power of electric currents to de- velop magnetism in soft iron is so great as to have led several philo- sophers to apply it to the production of a continuous movement, either rotatory or reciprocating. M. Jacobi, of St. Petersburg, was the first who constructed such a machine, and it was for a long time used in impelling a boat on the Neva. Since that time many electro- motors, as such machines are called, have been constructed ; the most important of these are by Loiseau, Froment, Lamanjeau, Page and Dumoncel. The late Mr. Sturgeon pumped water with an electro- magnet; Mr. Davidson, of Aberdeen, drove a turning-lathe by the same power ; and in 1848 we sailed at the rate of a mile in the hour in a boat thus impelled and constructed by Mr. Dillwyn, of Swansea. M. Jacobi, as we have stated, has been led by Dr. Faraday's dis- covery of magnetic electricity to abandon his expectation of obtaining anything like a valuable power from electro-magnetism ; and Messrs. Joule and Scoresby have come to the same conclusion. It appears from their calculations that a grain of coal consumed by a steam- engine in Cornwall will raise 143 lb. 1 foot, whilst a grain of zinc con- sumed in a voltaic battery can raise theoretically only 80 lbs. But MAONBTO-BLBOTRIO FOSOI. 209 the price of an hundred weight of coal is leu than 9 pence, whilst that of the same quantity of sine is more than 216 pence, so that under the most favourable conditions, the power obtained fVoni electro- magnetism must ooat twentyflve times as much as that