i88o.] The Baconian Philosophy of Heat. 691 
few months after Mayer, Mr. Joule, from experiments 
especially undertaken for the purpose, published values of 
his own of the same quality, previously but indirectly com- 
puted by Mayer. 
It is curious to note the different points of view which 
these three authors, as well as their predecessor Carnot — 
working, as far as is known, independently of one another, 
and with such diversified results — assumed relatively to the 
question of the intimate essence of heat. Carnot, who 
throughout his pamphlet had reasoned as if heat were a 
fluid capable of producing motion (but it was not proved 
owing to what cause) in the same way as flowing water does, 
had nevertheless explicitly asserted that heat was but mole- 
cular motion. Seguin and* Mayer, on the contrary, had 
considered heat and motion to be interchangeable ; but 
nevertheless the first of them pronounced the question as to 
the nature of heat to be for the present inapproachable, 
whilst the latter had distinctly denied that heat could be 
motion. Mr. Joule, finally, who was agreed on the 
mechanical question with his two last-mentioned prede- 
cessors, asserted at the outset, like Carnot, that heat 
essentially could only be motion. And this foregone 
conclusion of Mr. Joule, as soon as he had proved by 
decisive experiments that a given quantity of motion pro- 
duced under all circumstances the same quantity of heat, 
became, if not an irresistible, at least a most plausible, 
inference from faCts. Mr. Joule had found that the energy 
which, when involving finite motion, is expressed as 772 
footpounds may be converted into exactly one conventional 
unit of heat ; which, if it does not prove, finds at all 
events its most natural explanation in, the assumption that 
the unit of heat expresses similarly a quantity of energy, 
involving, however, no longer the finite motion of complexes 
of masses, but the infinitesimal excursions of the molecules 
of masses. Accordingly, in the conversion of motion into 
heat, or vice versa , there is no transmutation implied of two 
heterogeneous things into one another, but only a transfor- 
mation of finite excursions into infinitesimal, due to the 
transfer of velocities from entire bodies to their component 
molecules. If the measure of heat be only rational, or at 
least fixed, and thus indicate correctly the amount of motion 
gained or spent in each case, it cannot fail to result that a 
certain relation subsists between that measure and the 
measure of energies ordinarily applied to finite excursions. 
Actually, this relation is such, as demonstrated by repeated 
practical comparisons, that if a quantity of water be allowed 
