876 Prof. Tyndall's Remarks on the 



his celebrated essay f Ueber die Erhaltung der Kraft/ published 

 in 1847 : — "Joule has examined the quantities of heat generated 

 by the friction of water in narrow tubes, and in a vessel in which 

 the water was set in motion by a kind of turbine. He has 

 found in the first case that the heat which raises 1 lb. of water 

 1° C. would lift 452 kilogrammes to the height of 1 metre; 

 in the second case he found the weight to be 521 kilogrammes. 

 Nevertheless his methods of experiment correspond too little to 

 the difficulties of the investigation to allow of these results having 

 the least claim to accuracy " * (als dass diese Result ate irgendwie 

 auf Genauigkeit Anspruch machen kbnnten). I translated this 

 paper myself for the c Scientific Memoirs f/ and was careful to 

 append to this passage a note to the effect that Helmholtz when 

 he wrote thus was only acquainted with the earlier experiments 

 of Mr. Joule. Judged on broad and liberal grounds, Mr. Joule 

 is worthy of such praise as rarely falls to the lot of a philosopher. 

 He is, in my opinion, the true experimental demonstrator of the 

 dynamical theory of heat. But to write as you write regarding 

 his first experiments is simply to betray a want of acquaintance 

 with the requirements of refined experimental inquiry. 



You state in ' Good Words ' that Mayer's hypothesis is at best 

 only "approximately " true for air. Yes ; but the approximation 

 is so close that it cost Mr. Joule six years of labour, according 

 to his own methods, to arrive at the degree of accuracy attain- 

 able by the method of Mayer. You coldly deny to Mayer's first 

 paper all claim to novelty or correctness ; and yet a comparison 

 of that paper J with the first part of your " corrective" in ' Good 

 Words ' will show that the ideas which you have there enunci- 

 ated are the ideas of Mayer. The very illustration which you 

 employ, of stirring water in a basin to produce heat, is an experi- 

 ment of Mayer's mentioned in this first paper. In the subse- 

 quent portion of the article referred to, you come to what you 

 denominate "the grandest question of all." You put it thus : — 

 " Whence do we immediately derive all those stores of potential 

 energy which we employ as fuel or food ? What produces the 

 potential energy of a loaf or a beefsteak ? What supplies the 

 coal and the water-power without which our factories must stop ? " 

 These "grandest questions of all" were asked and answered by 

 Dr. Mayer seventeen years before you wrote your article; and 

 yet you never mention his name§. You proceed, "Whence 

 does the sun produce the energy which he so continuously and 



* See also Verdet, pp. 91 & 165. f 1853. 



I A translation of it is published in the Philosophical Magazine, vol. 

 xxiv. Ser. 4. p. 371. 



§ " Ces idees introduite pour la premiere fois dans la science en 1845, 

 par Jules Robert Mayer, font faire a la physiologie generate un progres 



