SIXTH ORDINARY MEETING. 41 



There can be now no doubt that the theoretical foundation for the 

 modern doctrine of the conservation of energy, of which the equiva- 

 lence of heat and work is a particular case, was distinctly and 

 substantially laid by the genius of Newton in his wonderful scholium 

 to his Third Law of Motion. 



In this scholium and in the commentary on it Newton not only 

 enunciates the law of conservation of energy, so far as the state of 

 experimental science in his day would permit, but also clearly antici- 

 pated the so-called modern principle of Vis Viva and D'Alemhert's 

 principle. No further advance of any moment seems to have been 

 made till about 100 years later Davy and Rum ford proved experi- 

 mental lv the immateriality of heat. To Rumford is mainly due the 

 credit of having rescued the question of the nature of heat from the 

 domain of metaphysics, and of having devised several ingenious 

 experiments, by means of which he arrived at a remai'kably approxi- 

 mate value of the mechanical equivalent of heat. The next im- 

 portant names in connection with the history of the theory of heat 

 are those of Fourier and Carnot. The calculations and conclusions 

 of these profound mathematicians were expressed, it is true, in terms 

 which to a certain extent involved the now exploded corpuscular 

 theories of light and heat, but their reasoning and results were 

 to such an extent independent of any particular theory that the 

 elements involving the truth of these untenable hypotheses are 

 capable of being almost entirely eliminated, leaving results which 

 have proved of the greatest use in the development of the true 

 theory of energy. Perhaps the most important of the many valuable 

 contributions of Clausius to the theory of heat was his adaptation 

 of the theorem of Carnot, so as to make it consistent with the prin- 

 ciple of the equivalence of heat and work. 



To Joule, the great English physicist, is undoubtedly due, as has 

 been conclusively shown by Prof. Tait, the credit of having placed 

 the grand law of the conservation of energy, of which the first main 

 principle of the mechanical theory of heat is but a particular case, 

 on a sure experimental foundation. By means of some of the most 

 ingenious and refined experiments of modern times, Joule deter- 

 mined that 772 foot-pounds of work, if converted into heat, would 

 raise I pound of water 1° F., or that to produce a quantity of heat 

 sufficient to raise 1 kilogramme of water through 1° C. work must 

 be consumed to the extent of 424 kilogrammetres, and thus placed 



