138 SCIENTIFIC THOUGHT. 



underlying unity and correspondence of all natural phe- 

 nomena, inasmuch as they all depend on the trans- 

 formation of a quantity, termed energy, which is in 

 many cases measurable in its best-known form i.e., as 

 energy of motion and, where this is not possible, in 

 the form of heat. 



Helmholtz had already, in 1847, summarily reviewed 

 the whole field, beginning with a restatement of the 

 fundamental formulae of dynamics in the light of the 

 new principle, and ending with a reference to the trans- 

 formation of energy in living vegetable and animal 

 organisms. The key to his explanations is to be found 

 in the introduction of a term to denote what becomes 

 of energy if it ceases to exist as energy of motion or as 

 a velocity, when it is changed to energy of mere position. 

 2 8. To this end he introduces the idea of stress or tension, 

 hoitzon The conception is already contained in older books on 



"tension." 



mechanics as latent force (Carnot), and the purely 

 mathematical treatment of dynamics by Lagrange and 

 Hamilton had prepared the ground by showing how all 

 dynamical problems could be reduced to the knowledge 

 of two quantities, the vis viva and the force function. 



1 L. N. M. Carnot (1753-1823), | gether with Monge, one of the 



usually termed the great Carnot, founders of modern geometry, of 



father of Sadi Carnot, member of the which more in a subsequent chapter. 



Directory, War Minister, and one : He introduced the principle of the 



of the most celebrated generals of I ' Correlation des Figures de Geo- 



France, has a name in science me'trie' (Paris, 1801). His books 



through his ' Essai sur les Machines ' were translated in Germany, where 



en ge'ne'ral ' (Dijon, 1784), his ' Prin- I they had a great influence. On his 



cipes fondamentaux de 1'Equilibre I connection with the history of the 



et du Mouvement' (Paris, 1803), as j conception of energy, see Bohn in 



well as through his ' Reflexions sur | 'Phil. Mag.,' iv. 300, vol. xxix. ; 



la Metaphysique du Calcul infi- j also Helm, ' Energetik,' p. 13 ; and 



nite'simal' (Paris, 1797) and his the Eloge by Arago of the year 



' Theorie des Transversales ' (Paris, 

 1806), by which he became, to- 



1837. 



