That this is the fact may be proven by a single reflection on the process of _combustion_. It is a daily observation that light is produced by _burning_ bodies. Let us suppose these bodies burnt at midnight in a close room; still light will be given out copiously and constantly. _Whence_ this light? The natural and obvious answer is, it was in combination in a _latent state_ with the burning bodies, and by combustion it was set free, and thrown out, and thus put the surrounding luminiferous ether in motion. It is said by some, the light evolved in this case is not from the burning bodies, but from the oxygen which is supplied by the air to support the combustion. This does not alter the case at all: for then the light was in combination with the oxygen, and was invisible, being in a latent state, until it was set free from the oxygen by combustion. The same conclusion is obtained in the process of _compression_ and _expansion_. If atmospheric air, or oxygen be suddenly compressed in a glass syringe; or if a glass ball, filled with the latter, be suddenly broke _in vacuo_, a _flash of light_ is instantly perceived. In this case the light suddenly becomes visible, which was invisible before, being latent in combination with the air. (URE.) We arrive at the same conclusion in case of _friction_. It is well known that pieces of wood can be made to _blaze_ by rubbing them together. But it is not so well known, that two pieces of rock crystal, or quartz, taken from any depth in the earth, and which cannot be supposed to have ever been in the light of the sun, when rubbed quickly together, even _under water, will give out volumes of light_. _Whence_ this light? from the quartz doubtless. Of course it must have been in a latent state, and was set free by friction. Let it be strictly observed, the crystals _never were exposed to the light of the sun, of course could not have derived this light from that luminary_. We must come to the same conclusion, in regard to the light given out by _animal_ substances. Many _insects_ are known to have the power of evolving light, or putting the surrounding luminiferous ether in motion, which is the same. Putrescent animal matter has been observed to possess it, in some cases, in a very great degree; sufficiently to illuminate a room, or pantry, for hours together. In some instances the fingers of those who touched the luminous flesh, became luminous.