41 
On the other hand it appears to Professor Tait just to 
quote a passage in which Helmholtz, no doubt in view of 
Mayer’s later work as well as that at the time of the found- 
ation of the science of mechanical effect, thus expresses 
himself : 
“ Mayer was not in a position to make experiments ; he was 
repulsed by the physicists with whom he was acquainted 
(several years later I was similarly treated), and could 
scarcely procure room for the publication of his first com- 
pressed exposition. You must know that in consequence of 
these repulses his mind at last became affected. It is diffi- 
cult now to transport oneself back into the circle of thought 
of that time and to perceive clearly how absolutely new the 
matter then appeared (25 years ago). It seems to me that 
even Joule had to struggle long for the recognition of his 
discovery. 
“ Thus although no one will deny that Joule has done far 
more than Mayer, and that in the early writings of the latter 
many points are not clear, I believe that Mayer must be 
considered as a man who independently and for himself dis- 
covered this thought which has produced the grandest 
recent advance of natural science, and his deserts are by no 
means diminished by the fact that simultaneously another, 
in another country and sphere of action, made the same dis- 
covery, and indeed has since developed it better than he.” 
Mayer has many titles to the gratitude of scientific men, 
and one of the chief of them will no doubt always be his 
anticipation of the true doctrine of the equivalence of heat 
and work. But as it was founded on an experiment which 
was only sound by chance, in interpreting which he had not 
seen that his conclusion depended on one precise answer to 
a question that had not suggested itself to his mind, it was 
anticipation and not discovery. Dr. Joule remains the true 
founder of the modern science of Heat. 
