II THE PROGRESS OF SCIENCE 8? 



be obtained at the expense of any other ; and ap- 

 paratus was devised which exhibited the evolution of 

 all these kinds of action from one source of energy. 

 Hence the idea of the " correlation of forces " which 

 was the immediate forerunner of the doctrine of 

 the conservation of energy. 



It is a remarkable evidence of the greatness of 

 the progress in this direction which has been 

 effected in our time, that even the second edition 

 of the " History of the Inductive Sciences," which 

 was published in 1846, contains no allusion either 

 to the general view of the " Correlation of Forces " 

 published in England in 1842, or to the publica- 

 tion in 1843 of the first of the series of experi- 

 ments by which the mechanical equivalent of heat 

 was correctly ascertained. 1 Such a failure on the 

 part of a contemporary, of great acquirements 

 and remarkable intellectual powers, to read the 

 signs of the times, is a lesson and a warning 

 worthy of being deeply pondered by any one who 



1 This is the more curious, as Ampere's hypothesis that vibra- 

 tions of molecules, causing and caused by vibrations of the 

 ether, constitute heat, is discussed. See vol. ii. p. 587, 2nd ed. 

 In the Philosophy of the Inductive Sciences, 2nd ed. 1 847, p. 239, 

 "Whewell remarks, d propos of Bacon's definition of heat, ' ' that 

 it is an expansive, restrained motion, modified in certain ways, 

 and exerted in the smaller particles of the body ; " that ' ' although 

 the exact nature of heat is still an obscure and controverted 

 matter, the science of heat now consists of many important 

 truths ; and that to none of these truths is there any approxi- 

 mation in Bacon's essay." In point of fact, Bacon's statement, 

 however much open to criticism, does contain a distinct approxi- 

 mation to the most important of all the truths respecting heat 

 which had been discovered when Whewell wrote. 



