216 Prof. Bohn on the History of Conservation of Energy, 



velopment and growth, during which they may be said to belong 

 to different persons. He who first expresses an idea with perfect 

 clearness and exactness is commonly regarded as the discoverer, 

 although in fact there be more than one entitled to this name. 

 Now this rule is also applicable to the question concerning the 

 author of the idea of transmutation of work of one kind into work 

 of another kind. This question, however, is complicated by a 

 circumstance which creates a difficulty in all researches on the 

 history of force, vis viva, of conservation of energy, and others : 

 these terms, as well as those of " work," " momentum of force," 

 " momentuoi of activity," " dynamical effect," " mechanical 

 power," "quantity of action," "quantity of movement," and 

 such like, are used by different authors, frequently even by one 

 and the same writer, in a different sense, and in so undefined a 

 manner that a sort of translation into the more precise scientific 

 language of the present day is required in order to clearly show 

 the meaning of the authors. 



In the Philosophical Magazine, S. 4. vol. xxviii. pp. 473, 474, 

 Dr. C. K. Akin quotes a few sentences from Placidus Heinrich and 

 Dr. Mohr, which he considers as the earliest statements of the 

 " allotropy of force." It appears to me, however, that it is essen- 

 tially left to the individual judgment of the reader whether he 

 will or will not find in those sentences a certain proof of the 

 author's firm conviction of possible transmutation of common 

 mechanical work into heat or electricity, and vice versa. 



In my opinion the following remark of L. N. M. Carnot is 

 more striking and less ambiguous than the above-mentioned 

 quotations of Dr. Akin. 



" Vis viva can figure either as the product of a mass and the 

 square of its velocity, or as the product of a moving power and 

 a length or a height. In the first case it is a vis viva properly 

 called, in the second it is a latent vis viva." 



This seems to show that, according to Carnot^s meaning, the 

 vis viva consumed in raising a weight or performing other work 

 is latent or stored up, and may be again employed in reproduc- 

 tion of a motion, or in the performance of another work at the 

 cost of the first done work. This appears more evidently from 

 another passage from Carnot : — 



" All effects of propelling powers {forces mouvantes) may be 

 compared to the raising of a weight to a certain height, and con- 

 sequently to a vis viva, be it a real or a latent one." 



For these statements I refer to Carnot' s Principes de Vequilibre 

 et du mouvement ; they are surely to be found in the edition of 

 1803, perhaps already in the first (of 1783), whereon, not having 

 the books at hand, I am not able at present to decide. For 

 the same reason I was unable to quote literally ; but I trust 



