THE LAW OF SUBSTANCE. 469 



the animal, and accepting Kumford's statement that the work was that 

 which could be readily performed 'by a single horse/ the writer showed 

 that the quantity of heat developed in Kumford's experiments, com- 

 pared with the accepted datum, 25,920 foot-pounds per minute as the 

 power of the horse, as given by Eankine, for the average case, or better, 

 say 25,000 for the average Bavarian horse of the last century, we obtain 

 as the 'mechanical equivalent/ 783.8 foot-pounds, differing from 778, 

 the accepted figure of Rowland and later authorities, by but six units, 

 less than 1 per cent, of its own value and vastly nearer than any figures 

 obtained up to our own time. 



Thus, as the writer claimed in 1873, we may state the achievement 

 of that great philosopher and engineer in the following terms: 



1. Eumford was the first to prove experimentally the immateriality 

 of heat. 



2. He was the first to indicate and directly to prove it to be a form of 

 energy; publishing his proof a year before Davy. 



3. Eumford first, a half -century before Joule, determined by experi- 

 mental research the quantivalence of thermal and dynamic energies, and 

 secured data giving the value of the factor of equivalence with almost 

 perfect accuracy. 



4. He is entitled to the sole credit of the experimental discovery of 

 the true nature of heat, of its equivalence with mechanical energy and 

 its measure of quantivalence. 



The work of Sir Humphry Davy was of great importance; but it was 

 in confirmation of the deductions previously announced to the Eoyal So- 

 ciety by his contemporary and colleague, Eumford. 



"Benjamin Thompson, of Concord, New Hampshire, commonly 

 known as Count Eumford, the Bavarian, should be accorded a higher 

 position and a nobler distinction than has yet been given him by writers 

 on thermodynamics."* 



Eumford, above all others, ancient or modern, is entitled to the 

 credit of not only laying down an experimental foundation for the 'Law 

 of Substance' and the principle of persistence of energy, but also for 

 actually making it a physical, rather than as previously a metaphysical, 

 topic; for proving the falsity of the older views of the nature and origin 

 of heat in thermodynamic systems, for proving by direct test and ex- 

 perimental investigation the immateriality of heat and its real character 

 as a 'mode of motion/ as Tyndall called it, as a form of energy more 

 properly. He furnished a method and means of estimating the 'me- 

 chanical equivalent of heat'; he originated by actual work of research a 

 true statement of the principle of the quantivalence of the two forms of 



* Transactions of the American Society of Civil Engineers, 1873. 'Note relating 

 to Rumford's Determination of the Mechanical Equivalent of Heat.' — Thurston. 



