Applying, then, this theory of the air thermometer, if we divide[B] 274° by 403,000,000--the number of times the density of the nebula was less than that of air--we get 0·00000068°, as the absolute temperature of the nebula, something very different to excessive heat, incandescence, firemist, or any other name that has been given to its supposed state. Furthermore, as a cubic foot of air weighs 565·04 grains, 403,000,000 divided by 565·04, which is equal to 713,223, would be the number of cubic feet of the space occupied by the nebula, corresponding to each grain of matter in the whole solar system, which would be equal to a cube of very nearly 90 feet to the side. And as the only means by which the nebula could acquire heat would be by collision with each other of the particles of matter of which it was composed; to conceive that two particles weighing 1 grain each, butting each other from an average distance of 90 feet, could not only bring themselves, but all the space corresponding to both of them--which would be 1,426,446 cubic feet, _of what_?--up to the heat of incandescence, or excessive heat of any kind, is a thing which passes the wit of man. Consequently, neither by primitive piling up, nor by collisions among the particles, could there be any heat in the nebula at the dimensions we have specified, beyond what we have measured above. [B] Here we beg to state that in all our coming operations, we will use the Centigrade Scale for temperatures without adding C to each number specified, unless a different scale has to be referred to, in which case the distinctive of the scale shall be given in the usual way. This we do because it is the fashion, not because we think it possesses any advantage over any other scale, but rather the contrary. Perhaps we may have something more to say about scales after we have handled the Centigrade a little more than it has been our lot to do hitherto. Some people believe, at least they seem to say so, that meteors or meteorites colliding would knock gas out of each other, sufficient to fill up the empty space around them, and become incandescent, and so pile up heat in nebulæ sufficient to supply suns for any number of millions of years of expenditure. But they forget that gas is not a _nothing_. It possesses substance, matter, of some kind, however tenuous. Therefore, if the meteors knock matter out of each other in the form of gas, they must end by becoming gas themselves, and we come back to what we have said above; we have two grains, in weight, of gas abutting each other at an average distance of 30 yards, instead of two grains of granite or anything else, and things are not much improved thereby. And if we compare 30 yards with M. Faye's 3000, where are we? The next thing to deal with is the formation of the planets. SEPARATION OF RING FOR NEPTUNE.