692 The Baconian Phitosophy of Heat. [November, 
to fall through the space of 772 feet, and the complexual 
velocity of 222 feet which it has then acquired be coverted 
into molecular velocity by arresting the further fall of the 
whole mass, the temperature of the water will have increased 
iust i° Fahr. This is what is understood by— and only m 
this way can be really understood— what is called the 
mechanical equivalent of heat . . , 
Thus the most natural inference to be derived from the 
investigation of the generation of motion by heat, or vice 
versa , strongly corroborates the truthfulness of the Baconian 
notion of heat. Soon after Mr. Joule’s experiments, this 
view was adopted by notable physicists and mathematicians, 
being almost immediately applied by Mr. Joule himself to 
the explanation of the theory of gases a task in which e 
unconsciously only reproduced the previous results of 
Bernoulli, which later again were re-discovered by Dr 
Kronig. This subjeft has since been fully developed and 
brought to a considerable pitch of perfection by several 
authors, to whose labours and authority it is not a little 
due that the Baconian philosophy has since found a great 
number of adherents. But whilst the researches we have 
hitherto mentioned all confirm the adequacy of the Baconian 
view to explain known faCts, there is another field of 
investigation whence proof may be derived of, perhaps, its 
necessity. Even more intimately connected with the question 
before us than the phenomena hitherto discussed are those 
designated by the name of radiant heat ; and these, more 
than any other, afford us the diredt clue to the 
nature of heat. Nearly two. centuries ago, Manotte 
apoarently succeeded in separating the effects of lg rom 
those of heat, from which it seemingly followed that these 
agents must be different also as to their origin. On the 
other hand, numerous experiments had indicated a certain 
similarity between light and heat under particular con- 
ditions, especially as to their mode of prorogation ; hence it 
was concluded that heat was capable of manifesting itself 
under certain circumstances in a form which, from its 
similarity to radiant light, was called radiant heat. What 
radiant heat really was, very few philosophers even of the 
first half of this century understood ; yet Newton, nearly 
two hundred years ago, had given an accurate account ot it. 
According to Newton, what is called radiant heat are the 
vibrations— or, more correftly, the undulations— of an 
all-pervading ethereal medium, concerned also in the pro- 
pagation of light, and which, arising from the vibrations of 
the molecules of bodies called hot or warm (but whose 
