Auckland Institute. 515 



in the words of Tyndall : "The great and now universally received doctrine, 

 that throughout the universe the sum of potential and actual energy is constant ; 

 that to create or annihilate energy is as impossible as to create or annihilate 

 matter, and that all the phenomena of the material universe consist of 

 transformations of energy alone." (Tyndall, " Heat," 132.) 



Now, if heat and force are convertible, and are really one and the same 

 thing in different forms — as had been suggested more or less clearly by many 

 philosophers ever since Bacon — then there must be some definite quantity of 

 heat corresponding to, nay, in fact, identical with or equivalent to, a given 

 amount of force ; and until this relation was established on undeniable 

 data the doctrine was an hypothesis only, and not a theory. 



This relation Dr. Joule, a man actively engaged in other pursuits, set 



himself to determine by direct experiments, planned and effected with an inge- 

 nuity as admirable as the perseverance which carried him over the comparative 

 failures of several years. A little preceding him, Dr. Mayer, of Heilbronn, 

 had thought out the same result, but it needed the patient industry of Joule 

 to confirm it by irrefragable evidence. Commencing in 1843, and continued 

 to 1849, Joule endeavoured, by extremely varied methods, to ascertain exactly 

 the effect in foot-pounds which arises from warming one pound of water 1° of 

 Fahrenheit : his results ranged in the earlier years from 1040 foot-pounds 

 to 770, discrepancies which arose from the inevitable imperfections in the 

 elaborate and delicate appliances and precautions required for such very subtle 

 investigations, but by the later period named these difficulties had been so 

 far overcome that the variation between the highest and lowest of his 

 determinations in 1849 was reduced to less than l-340th part; and the 

 contemporaneous reasonings and inferences of Mayer having led him to a very 

 nearly identical but slightly lower number ; the actual equivalent of heat has 

 been, I believe I may say, universally adopted as 772 foot-pounds. To quote 

 the words of Dr. Carpenter, in his presidential address to the British Associa- 

 tion, last September: " The unit of force which all scientific men, in all parts 

 of the world, now accept, on the basis of Dr. Joule's researches, as expressing 

 the equivalent of heat and mechanical force — that unit is called a Joule." 



It is scarcely possible to over-estimate the changes in all branches of the 

 analytical study of nature which result from this doctrine of the Conservation 

 of Force, and the recognition of the constantly active forces of the molecules of 

 all matter, which necessarily flows from it. By it every view of chemistry 

 and physics has been modified, and all, but especially those forms of chemical 

 action w T hich result in the development of electricity, have come to be under- 

 stood in a manner as widely different from, and as much clearer than, those 

 which prevailed in my youth, as the motions of the heavenly bodies were after 



the establishment of the Copernican System. The observation, for instance, 



