ON HEAT AS A MODE OF MOTION. 
117 
cuity, and with more copiousness of illustration. He adopts the same hypothesis 
as the latter philosopher, viz. that the heat evolved on compressing an elastic 
fluid is exactly the equivalent of the compressing force, and thus arrives at the 
same equivalent, viz. 365 kilogrammes per IT Centigrade. It must be re¬ 
marked that at the time Seguin and Mayer wrote, there were no known facts 
to warrant the hypothesis they adopted. There was no reason to assert that the 
heat evolved by compressing a gas was even approximately the equivalent of the 
compressing force. This being the case, may account for the inattention of the 
scientific world to these waitings. The dynamical theory of heat certainly was 
not established by Seguin and Mayer. To do this required experiment; and I 
therefore fearlessly assert my right to the position which has been generally ac¬ 
corded to me by my fellow-physicists as having been the first to give a decisive 
proof of the correctness of this theory.” Mr. Joule concludes by stating that 
he lays claim to no monopoly of merit, as others have materially assisted to de- 
velope the dynamical theory, nor does he w r ish in the slightest degree to detract 
from the personal ability and the intrinsic value of Mayer’s original researches. 
Whereon Tyndall, on his return from Switzerland, wrote the reply that now' forms 
the last appendix in his book. He begins with saying that he had in his lec¬ 
tures made full acknowledgement of the claims of Mr. Joule, and continues 
thus:—“ It was not my object, in the lecture to which you refer, to give a his¬ 
tory of the mechanical theory of heat, but simply to place a man of genius, 
to whom the fates had been singularly unkind, in a position in some measure 
worthy of him. I was quite aware of all that you have stated regarding Locke, 
Itumford, Davy, and others ; you might have added Bacon to your list. Proba¬ 
bly no great generalization was ever established without having first simmered 
in the minds of many thinkers. But the writings of Mayer form an epoch in 
the history of this subject; and I certainly should not feel disposed to retract 
a single sentence that 1 have written in his favour; I believe he deserves more 
praise than I have given him. It was he who first used the term ‘ equivalent 1 
in the precise sense in which you have applied it; he calculated the mechanical 
equivalent of heat from data which, as I have said, ‘ a man of rare ingenuity 
alone could turn to accountand his calculation is in striking accordance with 
your own experimental determinations. You worked independently of Mayer, 
and in a totally different way. You brought the mechanical theory to the test 
of experiment, and in this way proved its truth.” He goes on to state that 
Mayer made his deductions from known existing data, and that the best proof of 
his actual claim w r ould be the republication of his memoirs in a translated form. 
The second episode is the review contained in the 4 Athenaeum,’ April 25, 
1863, which indeed was the first incentive towards an attempt to produce some¬ 
thing more definite and reliable. The writer has hinted his praise and blame in 
such mild and uncertain phraseology as to leave no doubt that his sole acquaint¬ 
ance with the subject was the little he had skimmed at hap-hazard from the 
book. But short as is the notice, it contains a sentence the lecturer has thought 
fit to answer. 
u The mountain, upon whose ‘ heaven-kissing ’ summit is seated the angel 
of truth, is not to be assailed in the spirit which has given so much celebrity to 
our author, amidst the snow-clad mountains of Switzerland. The impetuous zeal 
by which the summit of Mont Blanc was achieved will not avail in climbing 
into the higher, the sublimer regions of truth !” and he then quotes the one 
rhetorical paragraph in the book, describing the power and the action of the sun. 
Writers as well as speakers have often the very excusable vanity of ending with 
a little glory ; it seems hard that a man may not be allowed to wind up twelve 
laborious lectures with a flourish, especially w r hen the flourish is only a poetical 
word-rendering of the more sober truth ; it seems harder still that such should 
be given as the specimen of his style. Here is the reply :— 
