PHYSICAL FORCES, CORRELATION OP 



PHYSICAL FORCES, CORRELATION OF. i : 



(whe* w consider the relations of hat and light, thus Ukou tantsMr 

 to b* otwr physical forces) that they in reality an the initiating 

 forms of nature, and that when they aeam to b produced by the other 



faross, they are, in fact, merely evolved from them. Much evidence 

 might be adduced from natural phenomena, and the reculu of experi- 

 mental reeearoh, in favour of tins view of the subject. But heat and, 



light appear to have the power of producing the other force* from the 

 moment of their own origination ; and the broad induction front the 

 actual state of our knowledge of their radiation is that they originate 

 in union, and in an abeolute aenie are inseparable, both being always 

 present, though in variable propartioni to each other ; with, at the 

 aune time, a certain reciprocity of preeence and activity, the one taking 

 the pUrt of the other to the extent, or in the degree, to or in which 

 the other u absent. The recent experimental researches on radiation 

 of M. Foucault, Mr. Balfour Stewart, and Professor Kirchhoff (' Proo. 

 of Hoy. Soo.,' and ' 1'hil. Mag.,' 1860, Ac.), seem to furnish irrefragable 

 evidence on thU point ; and a remarkable example of the reciprocity 

 here alluded to, in the relation of animal heat and animal light to each 

 other, was pointed out by Mr. Bray ley, in a lecture delivered at the 

 London Institution in 1833, the substance of which was communicated 

 to the Natural History section of the British Association in that year, 

 but not printed till 1835, when it appeared in ' Phil. Mag.,' third seriea, 

 voL vi pp. 941-247. 



Electricity is characterised by the author of the theory of the cor- 

 relation of physical forces, " as that affection of matter or mode of 

 force which moat distinctly and beautifully relates other modes of 

 force, and exhibits, to a great extent in a quantitative form, its own 

 relation with them, and their reciprocal relations with it and with 

 each other." Commencing with it as an initiating force, we get motion 

 directly produced by it, in various forms ; for instance, in the attraction 

 and repulsion of bodies,* and in the deflection of the galvanometer 

 needle. Electricity directly produces heat, as shown in the ignited 

 wire, the electric spark, and the voltaic arc. In these phenomena, 

 also, it directly produces light, of the greatest known intensity. It 

 directly produces magnetinu, as originally shown by Derated in his 

 great discovery [ELECTRO-MAGNETISM]. Lastly, electricity produces 

 ektmical qftmty ; and by its agency we are enabled to obtain effects of 

 analysis or synthesis with which ordinary chemistry does not fur- 

 niah us. 



Light is, perhaps, that mode of force the reciprocal relations of which 

 with the others have been the least traced out. Until the discoveries 

 of Niepoe, Daguerre, and Talbot [PHOTOGRAPHY], very little could be 

 definitely predicated of the action of light in producing other modes of 

 force. Viewing the phenomena of photography as resulting from a 

 function of light, we get the latter as an initiating force, capable of 

 producing, mediately or immediately, the other modes of force. Thus, 

 it immediately produces chemical action ; and having this, we at once 

 acquire a means of producing the others. In Mr. Grove's lectures at 

 the London Institution in 1843, already mentioned, he showed the 

 following experiment by which the production of all the other modes 

 of force by light is exhibited. " A prepared daguerreotype plate is 

 enclosed in a box filled with water, having a glass front, with a shutter 

 over it. Between this gloss and the plate is a gridiron of silver wire ; 

 the plate is connected with one extremity of a galvanometer coil, and 

 the gridiron of wire with one extremity of a Breguet's helix : the other 

 extremities of the galvanometer and helix are connected by a wire, and 

 the needles brought to zero. As soon as a beam of either daylight or 

 the oxyhydrogcn light is, by raising the shutter, permitted to impinge 

 upon the plate, the needles are deflected. Thus, light being the 

 initiating force, we get chemical action on the plate, electricity circu- 

 lating through the wires, maytuiitm in the coil, htat in the helix, and 

 *M*WM in the needles." 



Light would seem directly to produce heat in the phenomena of 

 what is termed absorption of light. Whenever light is absorbed heat 

 takes its place, affording us apparently an instance of the conversion of 

 light into heat; and of the fact, that the force of light is not, in reality 

 absorbed or annihilated, but merely changed in character, becoming in 

 this insrsnoe converted into heat by impinging on solid matter, as heat 

 is converted into light when solid incombustible matter becomes 

 intensely luminous by being introduced into highly-heated bat only 

 slightly luminous gas. The difference between the correlation of 

 light and heat and that of the other forces with each other, and 

 with them, has already been noticed, and will also be returned to in the 



Maynetum, at was proved by the Important discovery of Faraday 



[MAOIHTO-IXICTRICITT], will produce electricity, but with this pecu- 

 liarity, that in itoulf it is static ; and, therefore, to produce a dynamic 

 force, motion must be superaddod to it; it is in fact directive, not 

 motive, altering the direction of other forces, but not in strictness 

 initiating them, Magnets being moved in the direction of linos joining 



* It followi at a eonstqosset of the doctrine of the eomlstlon of fortes, thst 

 whea rU-ctricitjr performs any meehanlraj work which doct not return to the 

 machine, circuital power Is loet, baring been converted Into mechaaleal force. 

 In a diacoone 'On Inference* from the Negation of I'erpetnal Motion,' delivered 

 Jon* t), 1858, Mr. Orore performed an experiment In which this lots wu 

 rendered eidtnt. The acknowledged truth of the impouibility of pen ctual 

 motion U applied, deductively, la thU dlKourte, to Torifjr the doctrine of 

 correlalio-i. ( Proe. of the Moral Institution,' pp. 1SJ-1 J.) 



their poles, produce electrical currents in such neighbouring bodies as 

 are conductor* of electricity, in directions transverse to tho line of 

 motion. So if the magnet be stationary, conducting bodies moved 

 across any of the lines of magnetic force have currents of electricity 

 developed in them. Magnetism can, then, through the medium of 

 electricity, produce keat, ttykl, dumieal ajhiify, and molum. It can 

 itself be produced by these forces, but cannot produce them except 

 when in motion, which, therefore, is to be regarded in this oaso as the 

 initiative force. Magnetism will, however, directly affect the other 

 forces, light, heat, and chemical affinity, and change their direction or 

 mode of action, or, at all events, will so affect matter subjected to these 

 forces that their direction is changed. When this force, however, is in 

 what may be called its dynamic condition, that is, its state of change 

 at the commencement and the termination, or during the increment or 

 decrement of iu development, it will produce directly some of the 

 other forces, electricity and heat for example. " But it may be said," 

 observes Mr. Grove on this point, and the observation is important 

 with reference to the philosophy of the entire subject of the correla- 

 tion of physical forces, " while magnetism is thus progressive some 

 other force* is acting on it, and therefore it does not initiate." This he 

 admits to be true, but urges that " the same may be said of all the 

 other forces; they have no commencement that we can trace. \Ve 

 must ever refer them book to some antecedent force equal in amount 

 to that produced, and therefore the word initiation cannot in strictness 



remarked above, to a limitation of the truth of his views in this 

 respect. 



Chemical affinity, or the force by which dUainiilar bodies tend to 

 unite and form compounds differing generally in character from their 

 constituents, will directly produce motion of definite masses, by tho 

 resultant of the molecular changes it induces, of which the projectile 

 effects of gunpowder ore familiar instances. By chemical affinity, 

 again, we can directly produce electricity, and through its medium it 

 may be quantitatively converted into the other modes of force : but 

 heat and liyht are immediate products of chemical affinity, and che- 

 mical action produces magnctitm whenever it is thrown into a definite 

 direction, as in the phenomenon of electrolysis, a simple instance of 

 which Mr. Grove adduces as presented by his gas voltaic battery. 

 This completes the review of the phenomena arising from the 

 correlation of the physical forces, each taken in turn as the initiating 

 one. 



Mr. Grove states his belief that the same principles and mode of 

 reasoning as have been adopted in his Esuay, might be applied to the 

 organic as well as tho inorganic world ; and that muscular force, animal 

 and vegetable heat, Ac., might, and at some time will, be shown to 

 have similar definite correlations ; but that he boa purposely avoided 

 this subject, as pertaining to a department of science to which he hag 

 not devoted his attention. He alludes, however, to the experiments 

 of Professor Matteuci, by. which it appears that whatever mode of 

 force it be which is propagated along the nervous filaments, that mode 

 of force is definitely affected by currents of electricity ; and he states, 

 also, that by on application of the doctrine of the correlation of forces. 

 Dr. Carpenter has shown how a difficulty arising from the ordinary 

 notions of the development of an organised being from its germ-cell 

 may be lessened. 



In the 'Philosophical Transactions ' for 1850, pp. 727-757, is a 

 valuable paper by Dr. Carpenter 'On the Mutual Relations of the 

 Vital and Physical Forces," in which the principle of the correlation 

 of the latter U successfully extended in some detail to the i . 

 the subject of the germ-cell considered, as just alluded to, and, 

 the view of the correlation of the nervous and electrical forces, in 

 particular, which had been proposed by Dr. Carpenter some yean 

 before, and had been afterwards formally adopted by Professor 

 Matteuci, fully established. In this paper, perhaps the most impor- 

 tant general enunciation on the subject of correlation which has 

 followed Mr. Grove's ' Essay,' and certainly the first, of an adequately 

 definite and comprehensive nature, on the application of tho doctrine 

 to tho phenomena of organisation, the author states, that ho " in not 

 aware that any other attempt has been mode to furmularite the cntiro 

 series of these mutual relations, [the 'very intimate mutual relations 'of 

 the physical forces] than that which has been put forth by Professor 

 Grove in his short treatise ' On the Correlation, 4c." But Mr. Grove, 

 we must here remark, did much more than merely formularise 

 relations. He announced a new conception of their nature, whii -li 

 logically speaking, is a unirertul of physics, and this it is which given 

 his enunciation its true value, and elevates it almost to the rank of a 

 discovery. Another "f I>r. C;u Center's introductory remarks concerns 

 " a point on which," he says, " Professor Grove has not thought it 

 requisite strongly to dwell ; namely, the necessity for a certain material 

 luliitraliim as the medium " of the conversion of force. The existence, 

 however, of that substratum is a necessary implication of Mi. 1 

 entire doctrine. As he considers all the physical forces to be intrin- 

 sically affections of matter, understanding that term (to H~ 

 language of philosophical criticism) in its vulgar sense, the necessity 

 in question is an inseparable element of his theory, and is therefore 

 virtually dwelt upon throughout his Essay. 



