MEMOIR OF LAMARCK. 
31 
ivhere diffused and penetrating every substance, it 
is absolutely imperceptible : only, when it is put in 
vibration, it becomes the essence of sound ; for air 
is not the vehicle of soimd as natural philosophers 
believe*. But fire is fixed in a great number of 
bodies, where it accumulates, and becomes, in its 
highest degree of condensation, carbonic fire , the 
basis of all combustible substances, and the cause of 
all colours. When lesS condensed, and more liable 
to escape, it is acidific fire (feu acidifique ), the 
cause of causticity when in great abundance, and of 
tastes and smells when less so. At the moment 
when it disengages itself, and in its transitory state 
of expansive motion, it is caloric fire. It is in this 
form that it dilates, warms, liquifies, and volatilizes 
bodies by surrounding their molecules ; that it bums 
them by destroying their aggregation ; and that it 
calcines or acidifies them by again becoming fixed 
in them. In the greatest force of its expansion, it 
possesses the power of emitting light, which is of a 
white, red, or violet-blue colour, according to the 
force with which it acts ; and it is, therefore, the 
origin of the prismatic colours, as also of the tints 
seen in the flame of candles. Light, in its turn, 
has likewise the power of acting upon fire, and it is 
thus that the sun continually produces new sources 
of heat. Besides, all the compound substances 
observed on the globe are owing to the organic 
powers of beings endowed with life, of which, con- 
* Memoir on the substance of sound.— Journal de Physique, 
1 6 26 Brumaire, An. vii. 
