694 The Baconian Philosophy of Heat. [November 
rays. Now, if it be allowed, first, that invisible radiant 
heat and visible radiant heat (which is the same as radiant 
light) are essentially alike ; and secondly, that radiant light 
consists in undulations due primarily to molecular vibrations 
. — which latter point was even allowed by Newton and is 
confirmed by signal discoveries made within recent 
years — and which differ from radiant heat that is invisible 
only in the physiological accident of perceptibility by the 
eye ; it necessarily follows that what under all circum- 
stances when propagated from one body to another, produces 
effects of heat, and in animals sometimes produces the 
sensation of light besides, consists in those very molecular 
vibrations which, when of a certain pitch, are capable of 
giving us the sensation of light, but otherwise only the 
sensation of heat. In other words, from the correct inter- 
pretation of the phenomena of radiant heat it results that 
heat, “ its essence or quiddity,” as Bacon said, is motion. 
The fruitfulness of the Baconian definition of heat has, 
since the brief period of its revival, shown itself already in 
various ways, and it is impossible to overlook how great its 
influence is becoming in remodelling our traditional systems 
— if systems they may be called — of philosophy. Considered 
in its most enlarged aspect, it suggests an almost entirely 
new view of the whole of nature. In the words of the 
essay, of which the present forms an abstract : — “ If 
heat is motion — and this is the distinctive point of the new 
or revived philosophy — it follows, from all what we observe, 
that the condition of material existence in the universe is 
motion, not rest. We may imagine in our minds quiescent 
matter, but nature affords us no such example. Whatever 
may be thought of its horror of a vacuum, nature certainly 
seems to abhor rest. Not only is the condition of life in 
superior beings, as identified with the circulation of sap and 
blood, motion, but inanimate systems also seem unavoidably 
pervaded by motion. The earth as a whole moves, so do 
the other planets ; even the sun and the fixed stars move. 
And as in the solar and other starry systems in heaven each 
great component mass perpetually rotates round its central 
axis, revolves round its central body, and with it partakes of 
a motion in progression, or perhaps alternately backwards 
and forwards ; so every atom also in the most impalpable 
cluster of molecules — being, like all things in nature, im- 
pregnated with heat — rotates, revolves, advances, and 
retrogresses for ever in the infinitesimal space allotted as 
the scene of its ever-changing existence.” 
