when it is put in vibration, it becomes the essence of sound; for air is not the vehicle of sound as natural philosophers believe[3]. 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 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, consequently it may be said, that they are not conformable to nature, and are even opposed to it, because they unceasingly reproduce what nature continually tends to destroy. Vegetables form direct combinations of the elements; animals produce more complicated compounds by combining those formed by vegetables; but there is in every living body a power which tends to destroy it; all therefore die, each in his appointed season, and all mineral substances, and all organic bodies whatsoever, are nothing but the remains of bodies which once had life, and from which the more volatile principles have been successfully disengaged. The products of the most complex animals are calcareous substances, those of vegetables are argils or earths. Both of these pass into a siliceous state, by freeing themselves more and more from their less fixed principles, and at last are reduced to rock-crystal, which is earth in its greatest purity. Salts, pyrites, metals, differ from other minerals, only because certain circumstances have had the effect of accumulating in them, in different proportions, a greater quantity of carbonic or acidific fire.”