Mr. P. G. Tait on the History of Thermo-dynamics. 289 



blish when, in consequence of his lecture on "Force," we wrote 

 our article in ' Good Words J nearly two years ago. 



We have all along held that the questions as to the nature of 

 heat, and its equivalence to mechanical energy, were settled by 

 Davy; and that Rumford experimentally obtained a very fair 

 approximation to the equivalent. Also that, as Newton had 

 completely enunciated the Conservation of Energy in ordinary 

 mechanics, Davy's experiments brought heat under the same law, 

 and that, therefore, in the beginning of the present century the 

 Dynamical Theory of Heat was completely established, although 

 not developed. The development has been since furnished by the 

 experiments and reasonings of Joule on Electric Thermo-dyna- 

 mics*, his experimental determinations of the mechanical equi- 

 valent, his experiments and reasoning on the thermal effects of 

 the condensation and rarefaction of airf ; and by the theoretical 

 writings of Helmholtz, Clausius, Rankine, and Thomson. 



Hence, so far as regards the question of heat alone, Mayer 

 has no title to the position Dr. Tyndall claims for him. He 

 did no more than repeat what Davy and Rumford had done 

 better j and he has never, so far as even Dr. TyndalFs partisan- 

 ship can show, attempted anything of the nature of either the 

 theoretical or experimental developments which have advanced 

 thermo-dynamic science during the present century. What, in 

 point of fact, did Mayer do in thermo-dynamics ? In 1842 he 

 published a paper, of which Prof. Thomson and I remarked as 

 follows. "In this paper the results obtained by preceding 

 naturalists are stated with precision — among them the funda- 

 mental one of Davy — new experiments are suggested, and a 

 method for finding the dynamical equivalent of heat is pro- 



* Of these the following are perhaps the most important : — 



"On the Production of Heat by Voltaic Electricity " (Proc. Roy. Soe. 

 Dec. 17, 1840). Printed in Phil. Mag. 1841, with the title " On the Heat 

 evolved by Metallic Conductors of Electricity, and in the Cells of a Bat- 

 tery during Electrolvsis." 



" On the Electric Origin of the Heat of Combustion " (Phil. Mag. 1841). 

 Extension of the same (Report of British Association, 1842). 



" On the Heat evolved during the Electrolvsis of Water " (Lit. and 

 Phil. Soe. of Manchester, Jan. 1843). 



" On the Calorific Effects of Magneto-Electricitv, and the Mechanical 

 Value of Heat" (Phil. Mag. 1843). 



"On the Heat disengaged in Chemical Combinations," sent to the 

 French Academy in 1846 (Phil. Mag. 1852). 



" On the Mechanical powers of Electro-magnetism, Steam, and Horses," 

 by Scoresby and Joule (Phil. Mag. 1846). 



" On the Economical Production of Mechanical Effect from Chemical 

 Forces" (Manchester Memoirs, 1852, and Phil. Mag. 1853). 



t " On the Changes of Temperature produced by Rarefaction and Con- 

 densatiou of Air," sent to the Roval Societv, June' 1844 (printed in Phil. 

 Mag. 1845). 



