493 



PHYSICAL FORCES, CORRELATION' OF. 



PHYSICAL FOECES, CORRELATION OF. 



494 



Dr. Carpenter has lately (Feb. 24, I860) returned to this subject, in 

 a discourse delivered at the Royal Institution, and printed in the 

 ' ProceedingM ' at the meetings of tl e m jmbers, vol. iii., pp. 206-209, ' On 

 the Relation of the Vital to the Physical Forces.' Heargues.tliat when 

 we carefully look into the question, we 6nd that wliat the germ really 

 supplies is not the force but the directive agency. This agency may be 

 regarded, he observes, like magnetism, as a ttatic force ; and just as 

 magnetism requires to be (as we have already seen from Mr. Grove) 

 combined with motion to enable it to develope electricity, so does the 

 directive agency of the germ need the co-operation of a dynamic force 

 for the manifestation of its organising power. That dynamic force is 

 heat, the influence of which upon the rate of growth and development, 

 both animal and vegetable, is BO marked as to have universally 

 attracted the attention of physiologists, who, however, have only 

 recognised in it a vital stimulus, calling forth the latent power of the 

 germ, instead of looking upon it as itself furnishing the power that 

 does the work. It is indeed only when the physiological survey is 

 extended from the vital phenomena of warm-blooded animals to those 

 of cold-blooded animals and of plants, that the immediate and direct 

 relation between heat and vital energy, aa manifested in the rate of 

 growth and development, or of other changes peculiar to the living 

 body, is unmistakeably manifested. "Hence," Dr. Carpenter con- 

 cludes, after summarily reviewing the phenomena of vegetable life 

 under this point of view, " we seem justified in affirming that the 

 correlation between heat and the vital force of plants is not less 

 intimate than that which exists between heat and motion. The 

 special attribute of the vegetable germ is its power of effecting the 

 metamorphosis, and of utilising the organising force according to the 

 plan of construction characteristic of each species." 



For the details of Mr. Grove's own illustrations and applications of 

 his doctrine, we must refer to his work itself, in which, also, are given 

 his views of the intrinsic nature of the physical forces ; views which 

 are inseparable, in his opinion, from the dogma of their correlation. 

 In this, howpver, we cannot agree with him. That dogma, we con- 

 ceive, will remain a concrete expression of the truth, as a frit approx- 

 imation of great generality, and in point of time the first approximation 

 to a general theory, whatever notion may be finally established of the 

 nature of the forces concerned, and whether heat, for instance, be 

 regarded as a motion of the particles of ordinary matter that is of the 

 matter exhibiting its phenomena or as a motion of a calorific ether 

 pervading that matter. This discrimination we believe will be found 

 important in the further application and investigation of the subject. 

 In the article GROVE, WILLIAM ROBERT, in the BIOGRAPHICAL DIVISION 

 of this work, some remarks relevant on this head, have been offered 

 with respect to the history and interpretation of the principle of the 

 Correlation of Physical Forces, to which we may now refer as com- 

 pleting, together with the present and following remarks, our view of 

 the subject. 



Dr. Faraday's brilliant series of discoveries respecting the forces of 

 nature, and their relations to each other and to matter, of which 

 Volta's discovery of the pile, Davy's application of it to electrolysis, 

 Oersted's discovery of electro-magnetism, Seebeck's of thermo-elec- 

 tricity, Tyndall's of tho relation to structural density of para- and 

 dia- magnetism, and Mr. Grove's own discovery of the gas-battery, may 

 be cited as parallels of single terms in that series, have probably 

 contributed more than those of any other experimental philosopher to 

 prepare the scientific public mind for the idea of correlation ; and they 

 have had this effect, not only on account of their aggregate magni- 

 tude, as constituting so great a part of the advance in physics made 

 during the last sixty years, but because, from their bearing so exten- 

 sively on what Dr. Faraday calls " the dual forms of power," electricity 

 and magnetism, they have exhibited both the actuality of physical 

 correlation, and the convertibility of force, in a manner so palpably 

 intelligible. In the relations subsisting between positive and negative 

 electricity, and north and south magnetism, respectively, we have 

 the mental idea of correlation realised to sensible perception. The 

 relation of those forces themselves is probably a not less perfect cor- 

 relation, though perhaps of a different order; while their mutual 

 tibility, in which electro-magnetism and magneto-electricity 

 originate, is so readily demonstrated by experiment. 



In an addition (June, 1858) to his discourse on the " Conservation 

 of Force," (a designation introduced we believe by Helmholz, 

 in advocating a principle long tacitly admitted in particular cases, 

 but which had not before been explicitly recognised in its true 

 generality,) delivered in the preceding year (Exp. Res. in Chem. 

 and Phya. p. 461-462), Dr. Faraday says "Those who admit the 

 possibility of tho common origin of all physical force, and also 

 acknowledge the principle of conservation, apply that principle 

 to the sum total of the force. Though the amount of mechanical 

 force (using habitual language fur convenience sake ) may remain 

 unchanged and definite in its character for a long time, yet when, 

 as in the collision of two equal inelastic bodies, it appears to 

 be lost, they find it in the form of heat, and whether they admit 

 that heat to be a continued mechanical action ( as is most pro- 

 bable), or assume some other idea, as that of electricity, or action of 

 a heat-fluid, still they hold to the principle ol conservation by 

 admitting that the sum of force, that is, of the ' cause of action,' is 

 the same, whatever character the effects assume. \Vith them the 



convertibility of heat, electricity, magnetism, chemical action, and 

 motion, is a familiar thought." This is forcibly put, and is perfectly 

 true ; but the mutual convertibility of the forces enumerated has only 

 become " a familiar thought " since Mr. Grove's announcement of the 

 | principle of their correlation. No one, however, could have more 

 ' perfectly realised the conception of that principle, or appreciated its 

 i importance, than Dr. Faraday, as indeed the preceding extract may 

 itself show. The latest course of lectures delivered by him (and 

 published in the ' Chemical News ') consisted of ' Illustrations of the 

 Various Forces of Matter, t. e., of such as are called the Physical or 

 Inorganic Forces, including an Account of their Relations to each 

 other.' The subject of the concluding lecture, given on the 7th of 

 January last (1860), was, eo nomine, ' The Correlation of the Physical 

 Forces," of which many experimental demonstrations were shown, 

 relating chiefly to the change of chemical force into electricity, and of 

 electricity into magnetism ; and this eminent explorator of physical 

 truth, observing to his audience that he might show them many other 

 experiments by which he could obtain electricity and chemical 

 action, heat and light from a magnet, terminated his course by the 

 emphatic question, " But what more need I show you to prove the 

 universal correlation of the physical forces of matter, and their mutual 

 conversion one into another ? " 



A certain amount of anticipation of Mr. Grove's views has been 

 recently claimed by Professor Tyndall (' Glaciers of the Alps,' p. 300) 

 for the late M. Rendu, bishop of Annecy, the author of a remarkable 

 essay on glaciers, published in 1841. In considering what he calls the 

 'law of circulation," and after alluding to the circulation of water 

 through terrestrial nature, and that of the elements of organic sub- 

 stances from the solid to the fluid, and thence again to the state of 

 organisation, M. Rendu adds, " That universal agent which we 

 designate by the names fire, light, electricity and magnetism, has pro- 

 bably also a circulation as wide as the universe." But this is exactly 

 one of those comparatively vague notions, however true in their 

 degree, referring the forces of nature to a common principle, which 

 have been alluded to in the introductory part of this article, and to 

 which every period in the history of philosophy, for at least a century 

 before, supplies a parallel. When Professor Tyndall in sequence 

 claims also for Rendu, on the same account, a degree of anticipation of 

 Helmholz's more recent doctrine of the ' Conservation of Force,' quot- 

 ing the latter as saying in reference to the " circuit" formed by " heat, 

 light, electricity, magnetism, and chemical affinity," ' starting from 

 each of these different manifestations of natural forces, we can set 

 every other in action," he ascribes to Helmholz what had before been 

 explicitly enunciated by Grove, almost in the same words, as may be 

 seen in the preceding statement of his doctrine. 



Dr. (late Professor) James D. Forbes (' Reply to Tyndall on Rendu ') 

 has already noticed the futility of these claims ; but what he, by the 

 free application of meiosif, calls " the theoretical inferences of Messrs. 

 Grove and Helmholz," Faraday, as we havo seen, accepts as demon- 

 strated principles of nature, and Professor Le Conte, we shall presently 

 find, regards as forming "a necessary truth," and "one of the grandest 

 generalisations in modern science." 



Two remarkable circumstances have characterised the history of the 

 reception of Mr. Grove's doctrine of correlation. Many physicists and 

 others who admit in a general manner the principle, seem very unwill- 

 ing to use the term ; while others who explicitly adopt and advocate 

 both, seem equally unwilling to ascribe them to their author, and omit 

 all reference to him. 



Thus, hi Professor Lieblg-s ' Familar Letters on Chemistry' (1858), in 

 the preface to the fourth edition, the introduction of a letter (the 13th) 

 ' On the Correlation of the Forces of Inorganic Nature,' is announced in 

 the preface, but neither in that nor in the letter itself is Mr. Grove 

 mentioned, nor indeed are his views given, though his designation of 

 the subject is thus unreservedly employed. It is applied, in the 

 letter, chiefly to a view of natural forces taken by Dr. Mayer of 

 Heilbronn, asserting both their indestructibility and their converti- 

 bility, aa consequences of tho axiom Cauta wquat effectum, but 

 not dated, and apparently subsequent to the views both of Helmholz 

 and of Grove. 



The following introductory paragraph of an excellent paper by 

 Professor Le Conte, of South Carolina College, Columbia, U. S., ' On 

 the Correlation of Physical, Chemical, and Vital Force, and the Con- 

 servation of Force in Vital Phenomena/ contains one of the most 

 emphatic and adequate recognitions of the importance of those princi- 

 ples and intelligible terse statements of their nature which has yet 

 appeared ; though, even in this, no allusion is made either to Mr. 

 Grove or to M. Helmholz, and the uninformed reader might be led to 

 suppose that being necessary truths they had always been self-evident. 

 " Matter constantly changes its form, but is itself indestructible, 

 except by the same power which called it into being. The same 

 quantity of matter exists in the universe at all times. So also force 

 changes ita form constantly, but is itself indestructible, incapable of 

 increase or diminution, and the same absolute amount of force exists 

 in the universe at all times and for ever. The mutual convertibility 

 of the various forms of force is called ' correlation of forces.' The 

 invariability of the absolute amount in the midst of constant change 

 is called ' conservation of force.' This principle of correlation and con- 

 servation of force must be looked upon as one of the grandest 



