Page:Popular Science Monthly Volume 38.djvu/79

Rh It is impossible with our present knowledge to suppose that at any prior stage of the history of the heavens gravitation did not exist. It is impossible, from what we know now, to suppose that even the finest form of matter which entered our clearing in space was not endowed with motion. Given this matter, its motion and gravitation, let us next see what must very quickly follow.

Gravitation will give us a formation of centers; we shall get a rotation (moment of momentum) due to the prior existence of motion and to this formation of centers; we shall eventually in that way get condensing masses of this curdled substance.

The moment we have these centers formed, gravitation again will give us the motion of exterior particles toward these centers, and the condensation in one part of space will necessarily be counterbalanced by a clearing in another, so that, if we suppose that the curdling was not uniform to begin with, the uniformity will be less and less as time and this action go on.

Let us imagine that here and there we have isolated eddies, and here and there in the larger aggregations of the dust—in the most enormous swarms we can imagine—we have also eddies; these eddies involved in the larger curdlings will be associated with the phenomena of the general system of which they form an insignificant part. These cosmical molecules aggregating in this way will be, to compare great things with small, like the invisible molecules of a gas. It is not too much to say, as Prof. George Darwin has recently shown, that we shall have in effect the whole mechanism of the kinetic theory of gases before us; but, instead of dealing with invisible gaseous particles, we shall have particles, large or small, of meteoric dust. The kinetic theory tells us that if we have encounters we must have a production of heat; if we have production of heat we must have the production of radiation, although, if the heat be insufficient, the radiation may not produce light enough to be visible to the human eye.

It is a remarkable thought that all these changes to which I have so far drawn attention may have been going on in different parts of space for æons without any visible trace of the action being possible to any kind of visual organs. I refer to this because it is right that I should point out here that Halley, who was one of the first to discuss the possible luminosity of sparse masses of matter in space, and Maupertuis, who followed him, both laid great stress upon it. When, then, these encounters, which we may call collisions, take place, and when the heat due