690 The Baconian Philosophy of Heat. [November, 
necessities of practice itself seldom fail to start them anew in 
some shape or other; and to this general rule the problem 
touching the nature of heat has not been formed an exception. 
Whilst Davy and Rumford had attempted to settle the point 
by an investigation into the excitation of heat due to 
mechanical force, as in friction, it was now the study of the 
reverse process, or of the development of mechanical force 
by heat, as in the steam engine, by which the question was 
again brought under discussion. The first to start this 
practically, no less than theoretically, important inquiry 
into the production of motive power by the agency of heat, 
which until then had been negleCted, was S. Carnot ; who, 
in an essay published now just forty years ago, proposed a 
theory according to which the evolution of force by heat 
was owing to a degradation of temperature, not of bodies, 
which would involve losses of heat, but of quantities of 
heat, which thus remained undiminished— similarly as 
masses of water, by a change of level, can impart move- 
ment to other bodies without undergoing any material 
diminution. This view, though radically false, as must be 
apparent to any one who analyses the simile just employed, 
suggested by Carnot himself— involves nevertheless an 
element of truth of great praftical importance. And, in an 
equally singular and tortuous manner, the little pamphlet 
in which this theory was published contributed in a greater 
measure to revive, and ultimately re-accredit, sound notions 
on the nature of heat — including, by construction, the correa 
solution of the mechanical problem primarily attacked by 
its author — than almost any subsequent publication. Ere, 
however, the influence of Carnot’s essay had made itself 
felt upon this wider basis, the more limited question which 
he had attempted to solve had been fully determined. io 
this result three investigators contributed independent and 
diversified shares. M. Seguin, fifteen years after Carnot s 
contrary assertion, maintained that, in the production of 
mechanical force through the intervention of heat, heat was 
absolutely lost, and that between the amounts of heat so 
lost and the amount of force so gained there existed an 
invariable numerical ratio, which he attempted to calculate, 
but only with partial success. Starting from more com- 
prehensive premisses than Seguin, but agreeing with him 
in the particular question before us, Dr. Mayer, a few years 
later, succeeded in deriving the numerical value of the 
magnitude sought to be determined by Seguin, with as 
much accuracy as the then state of knowledge of the sub- 
sidiary data of his calculations permitted. Lastly, but a 
