472 POPULAR SCIENCE MONTHLY. 



tion of Force,'* in which he 'endeavored to ascertain all the relations be- 

 tween the different natural processes.' In his lecture of 1854, he 

 credits earlier writers on the subject, in the following order: Carnot 

 (1824), Mayer (1842), Colding (1843), Joule (1843), and states that he 

 was awakened to this work by the last-named. 



To the Carnot law, Helmholtz gives the following expression: 'Heat 

 only when passing from a warmer to a colder body, and then only par- 

 tially, can be converted into mechanical work.' 



This is obviously no other than the essence of the principle as not 

 only asserted, but actually proved, a quarter of a century before Carnot 

 by Benjamin Thompson and Humphry Davy, by direct experiment, so 

 far as it is an assertion of the convertibility of the two energies. Helm- 

 holtz acknowledges the indebtedness of the scientific world to Mayer, 

 whose paper 'On the Forces of Inorganic Nature' had been printed in 

 1842, that 'On Organic Motion and Nutrition' in 1845, and that 'On 

 Celestial Dynamics' in 1848; while his paper 'On the Mechanical 

 Equivalent of Heat' was not published until 1851. f 



Helmholtz concludes: 'Thus the thread which was spun in darkness 

 by those who sought a perpetual motion has conducted us to a universal 

 law of nature which radiates light into the distant nights of the begin- 

 ning and to the end of the history of the universe.' 



Dr. W. B. Carpenter, in a lecture before the Eoyal Society, published 

 later in their Transactions for 1851, summarized the work in this field, 

 to his date, under the title 'The Correlation of the Vital and Physical 

 Forces,' and showed, probably for the first time in this field, the unity 

 of the principle of equivalence of energies in organic and vital, as well 

 as in inorganic and lifeless nature. He attributes to Dr. Mayer, of Heil- 

 bronn, the first annunciation of the great principle of 'Conservation of 

 Force,' in its then broadest form, in his paper of 1845, already men- 

 tioned; while Carpenter considers his own paper of 1850 'On the Mutual 

 Eelations of the Vital Physical Forces, as the first announcement of 

 the extension of the law beyond the latter class of phenomena into the 

 range of vital energies. It is in his lecture on this subject that Carpen- 

 ter states the fact, since recognized perhaps most explicitly, among con- 

 temporary writers, by Haeckel, that 'what the germ supplies is not the 

 force but the directive agency.' 'The actual constructive force is sup- 

 plied by heat.' Even 'the life of man, of any of the higher animals, con- 

 sists in the manifestation of forces of various kinds, of which the or- 

 ganism is the instrument,' and, further: •' during the whole life of the 

 animal, the organism is restoring to the world around it both the 

 materials and the forces which it draws from it.' 



* It will be noted that it was very usual among these earlier writers to employ 

 'force' synonymously with 'energy,' as we now define the latter. 



f All these papers may be found in Youman's collection, already alluded to. 



