i88o.] The Baconian Philosophy of Heat . 689 
enclosing vessels. Other philosophers of eminence living 
in the last century, and amongst them notably Cavendish, 
concurred in the same view, or at least in that which 
generally averred the essence of heat to be motion ; and 
whilst some defended it, moreover, by arguments, two 
investigators of the highest fame in philosophy endeavoured 
to sustain it by experiments also. Sir Benjamin Thompson 
(Count Rumford) and Sir Humphry Davy, just as the cen- 
tury drew to its close, proved by decisive experiments that 
heat might not only be transferred, but actually evolved, or 
in a manner created, by fridtion ; which could not be the 
case if heat, as was then currently assumed, was a substance, 
but was intelligible enough if heat was allowed to be motion. 
The force of this argument as well as the naturalness of 
the whole view which made out heat to be motion, was 
well put in his celebrated “ Lectures on Natural Philo- 
sophy ” (delivered at the Royal Institution) by Dr. Young ; 
who, having by signal discoveries reinstated the true 
philosophy of light, thus contributed also to keep in 
some measure alive the true philosophy on the kindred 
subject of heat. And, though somewhat tardily, the 
prophecy which he uttered in reference to this matter has 
come right after all. With singular foresight and trust in 
the ultimate triumph of truth, Dr. Young in 1802, being the 
very time when the Baconian theory had become most dis- 
credited, expressed himself as follows : — “ It was long an 
established dodtrine that heat consists in the vibrations of 
the particles of bodies, and is capable of being transmitted 
by undulations through an apparent vacuum. This opinion 
has been of late very much abandoned. Count Rumford and 
Davy are almost the only modern authors who appeared to 
favour it : but it seems to have been negledted without any good 
reason, and will probably soon recover its popularity.” 
In point of fadt, it took the better part of a century to 
make this predidtion true. Wearied by the ceaseless, and 
for the most part baseless, metaphysical speculations which 
charadlerised the first decades of this century on the one 
hand, and on the other, dazzled by the prodigious develop- 
ment of the power of mathematics, which occurred at nearly 
the same time, natural philosophers had begun to shun all 
topics bearing ever so slight a resemblance to metaphysics, 
taking refuge instead in the processes of mathematics, which 
had been found capable of evolving the greatest multiplicity 
of pradtical results from the smallest possible stock of 
physical notions. Yet though by tacit consent purely 
theoretical questions may be generally eschewed, the 
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