Fire and light are easily proved to be dispersed through the whole air, from the immediate action of _speculums_; and that air itself is of the same substance with fire seems very plain; for as fire cannot subsist without air, (and in proportion to the quantity of air forced into the fire, in such proportion will be the force of the fire;) so, neither can fire act but on the outside of bodies next the air; for even the most inflammable bodies can only catch fire on their outermost surface contiguous to the air; and fire in action, if immerged in a body of the most inflammable matter, so as to leave no lighted part above such surface in the air, will be so far from kindling the inflammable body, that itself will be extinguished. Thus “if a flaming brimstone match be plunged into the highest rectified spirit of wine, the spirit of wine will extinguish it as intirely, as if dipped in cold water; it will also extinguish a live burning sparkling coal; but in the former experiment, if the least bit of the burning match remains above the spirit of wine, it will then catch fire, and the flame will presently spread over the whole surface.” This is an experiment of the great _Boerhaave_, in the first vol. of his chymistry, by _Shaw_, pag. 316. All these experiments, I think, prove to a certainty, that air is convertible into light. I shall now bring one experiment, from _Boerhaave_, Vol. 1. p. 998. which proves, that fire or light may be changed into air. “If a spherical glass vial be kept in a glass-house furnace, till ready to melt, and then be hermetically sealed in that heat, and suffered to cool; if now, it be held inverted, under cold water, and the end of the neck be carefully broken off, the water will be violently forced into it, and fill the glass, but so as to leave a bubble of true elastic air at the bottom.” The above experiments prove, that, whenever air is sufficiently divided or broken to pieces, light is produced; so that the light or heat in electricity, is no other than, we find, may be produced several other ways. For the air being violently rubbed or ground to pieces between your hand and the glass globe, whirled briskly about, the air between your hand and the globe is ground so small as to be in the form of _light_, which is expanded or sent off from the glass globe in the same manner as _light_ from a candle, or other luminous body; which emission is continually supplied by the common air pressing in between the rays of _light_, emitted from the glass ball. That this is the method, by which it acts, seems very clear: for you may not only hear the hissing noise of the air pressing towards the globe, but also plainly feel the air with your hand, near the globe or tube.