MEMOIR OF LAMARCK. 31 



where 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 sound 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 acidifiquej, 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 burns 

 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. 



