[21] Brugnatelli considered that oxygen, in certain cases of combination, entered into union with different bodies, without parting with its _caloric_; and in that state he gave it the name of THERM-OXYGEN; so that Davy had a precedent for his nomenclatural innovation. In following up this question, he would seem to consider Light as the _Anima Mundi_, diffusing through the universe not only organization, but even animation and perception. _Phos-oxygen_ he considers as capable of combining with additional proportions of Light, and of thus becoming '_luminated Phos-oxygen!_'--from the decomposition of which, and the consequent liberation of light, he seeks to explain many of the most recondite phenomena of Nature. We cannot but admire the eagerness with which he enlists known facts into his service, and the boldness with which he ranges the wilds of creation in search of analogies for the support and illustration of his views. He imagines that the _Phos-oxygen_, when thus _luminated_, must necessarily have its specific gravity considerably diminished by the combination, and that it will therefore occupy the higher regions of the atmosphere; hence, he says, it is that combustion takes place at the tops of mountains at a lower temperature than in the plains, and with a greater liberation of light. The hydrogen which is disengaged from the surface of the earth, he supposes, will rise until it comes into contact with this _luminated Phos-oxygen_, when, by its attracting the oxygen to form water, the light will be set free, and give origin to the phenomena of fiery meteors at a great altitude. The phenomenon termed '_Phosphorescence_,' or that luminous appearance which certain bodies exhibit after exposure to heat, is attributed by this theory to the light, which may be supposed to quit such substances as soon as its particles have acquired repulsive motion by elevation of temperature. The Electric Fluid is considered as Light in a condensed state, or, in other words, in that peculiar state in which it is not supplied with a repulsive motion sufficiently energetic to impart projection to its particles; for, he observes, that its chemical action upon bodies is similar to that of Light; and when supplied with repulsive motion by friction, or by the contact of bodies from which it is capable of subtracting it, it loses the projectile form, and becomes perceptible as Light. It is extremely probable, he adds, that the great quantity of this fluid almost everywhere diffused over our earth is produced by the condensation of Light, in consequence of the subtraction of its repulsive motion by black and dark bodies; while it may again recover the projectile force by the repulsive motion of the poles, caused by the revolution of the earth on its axis, and thus appear again in the state of sensible light; and hence the phenomenon of the _Aurora Borealis_, or Northern Lights.