32 Prof. Tyndall's Notes on Scientific History, 



16. In the Philosophical Magazine for April 1863, Prof. 

 William Thomson of Glasgow, and Prof. Tait of Edinburgh, 

 express themselves thus: — "Does Prof. Tyndall know that 

 Mayer's paper has no claims to novelty or correctness at all, 

 saving this, that by a lucky chance he got an approximation to a 

 true result from an utterly false analogy j and that even on this 

 point he had been anticipated by Seguin, who, three years before 

 the appearance of Mayer's paper, had obtained and published the 

 same result from the same hypothesis." I have nowhere in this 

 paper introduced italics into quotations; wherever they occur 

 they are in the original. 



17. And in reference to the same subject, a more recent 

 anonymous northern writer* expresses himself thus : — "Of 

 Seguin and Mayer, it seems not very difficult to estimate the 

 claims, so far as the true theory or the mechanical equivalent of 

 heat is concerned. Seguin in 1839, and Mayer in 1842, gave 

 as values of the mechanical equivalent : the first 363 kilogram- 

 metres, or, in terms of the ordinary British units, 660 foot- 

 pounds; the second the almost identical number 365 or 663. 

 It is curious also to observe that the methods employed are 

 almost identical.'" 



18. Did the reputation of Dr. Mayer depend on his calculation 

 of the mechanical equivalent of heat, and were the statements here 

 quoted correct, his right to the recognition which I have thought 

 his due might fairly be questioned. But let us inquire whether 

 this is really the case. The Table on which the claim for M. 

 Seguin is founded is now before the reader ; and on referring to it, 

 two columns will be seen, the one headed " Effet produit en kilo- 

 grammes eleves a 1 metre/' and the other headed " Temperatures 

 correspondantes a l'effet produit." The first number in the first of 

 these columns is 7270 kilogrammetres, and the "temperature cor- 

 respondante" is 20 degrees. Hence, dividing 7270 by 20, we have 

 the quotient 363 as the number of kilogrammetres corresponding 

 to a single degree. And so of the other pairs of numbers, which 

 give 363, or thereabouts, as the mechanical effect due to a single 

 degree. All this seems very plain ; and did no text accompany 

 the Table, and had not M. Seguin in that text explicitly defined 

 his own terms, w T e might be justified in assuming that he meant 

 the number 363 to stand for the mechanical equivalent of heat, 

 in the same sense as Dr. Mayer meant the number 365 to stand 

 for it. It is only necessary, however, to read the foregoing pages 

 to see that Mayer and Seguin are speaking of two totally different 

 things ; that the degrees of the one are not the degrees of the other ; 

 that tlie " temjjeratures correspondantes " of the latter, which refer 



* Not my Edinburgh reviewer, who, while he writes as a critic, knows how 

 to preserve the style of a gentleman. 



