Page:Popular Science Monthly Volume 13.djvu/360

346 this mass into the attracting spheres of surrounding stars, and thus beyond the possibility of return.

It may be proper, here, to point out the modus operandi by which such systems reach the state of quiescence alluded to above, which is, substantially, as follows:

The planets absorb their satellites by first converting them into fragmentary rings—as Saturn has already transformed two of his. These rings gradually approach the planets, till finally they fall upon their surfaces, and become part of them; while the planets themselves are approaching their primaries to succumb to a like fate.

Having absorbed their planetary attendants, and having cooled off so as to become cold, dark bodies, like the earth, they enter the sphere of each other's sensible attraction, and begin to approach with continually increasing velocity, till finally they meet, each arriving at the point of contact with a velocity of from 400 to 500 miles a second, depending on their mass and density.

Of the heat generated by such a collision, we can have no adequate conception. It may, however, be calculated, and written down in thermometric degrees; still the figures are meaningless to us except as representing an inconceivable intensity of heat.

It may be stated as so many thousand times the heat generated by the explosion of an equal weight of gunpowder, still we are unable to form an idea of the unit of measure here given.

If the doctrine of the "correlation and conservation of forces" be true, then the heat thus generated, if it could all be applied in the form of moving force to these two bodies while yet intact, should be sufficient to throw them back again to the points at which their motions began to be accelerated, if there were no resistance; but, owing to the resistance met with, they will not rebound fully to those points.

It will not, however, be expended in that manner, but in expanding the entire mass of these two globes into a thin, nebulous vapor; large portions of which, most probably, will be thrown out beyond the sphere of sensible attraction of that which remains, and into those of the surrounding stars.

This great probability will much resemble a certainty when we come to subject the question to the following speculative illustration: