William Morris Davis

“ 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. ”

“ That this satellite of Mars and others in our system were much farther away from their primaries than they now are, will be proved, by proving that, if a nebulous satellite revolved around any primary in the short period in which most of the solid ones now do, the tidal energy—or tendency to elongation and disruption—which would, in that case, be generated on its opposite sides by such rapid revolution, would be sufficient to tear it into atoms. ”

“ Assuming the density of the earth to be 512 times that of ice, it follows that, if a globe of ice—say ten miles in diameter—be isolated in space, a small dense body, as a bullet, near its surface, should fall toward it—by the action of its gravity alone—through 160 inches during the first minute of its descent. ”

“ Now, the tidal energy, as above calculated, causes the planet to pull the nearest pound with 1.6 grain greater force than it does the central pound, while, at the same time, it pulls the central pound with practically 1.6 grain greater force than it does the farthest pound; consequently the tensile pull between these two surface-pounds, which would be required to resist the tidal energy, must be equal to 2 x 1.6 grain, while they are drawn toward each other by the gravity of the satellite with the force of only 1.6 grain. ”

“ Or, in other words, it may be forming a new bud, which, when properly vivified by another one, may blossom forth with the most brilliant rainbow hues, and finally ripen into planetary fruit which shall become the happy home of future intelligent races. ”

“ If the entire nebulous mass could be preserved in the form of an expansible spherical shell, while the entire amount of heat-force should be acting upon its interior surface to force it outward, then, according to the above-named law of conservation, the entire mass would be thrown nearly to the limit of its sphere of sensible attraction ”

“ Density of the Newly-formed Nebula.—If, now, we fix our attention on the condition of this nebula at the moment when the explosive force had expended its last effort to throw these outside masses into surrounding space, we can readily see that it must have been of very nearly uniform density, in consequence of the tendency of the out-moving particles to continue their motions outward. ”

“ From the manner in which the solar system has been formed, it seems most probable that all the bodies in it should both revolve and rotate in the same plane and direction that the sun does, had there been no external disturbance to prevent it. ”

“ The disruptive ability of the tidal energy of a primary planet on a nebulous satellite of small but unvarying mass varies directly as the cube of the diameter and inversely as the square of the periodic time. ”

“ Let us direct our attention to two of them which are very like our star in mass and attendants, or we may suppose our sun to be one of them, and that they are so moving as to approach each other at the very slow rate of one mile a week ”

“ The object of assuming such slow original motion for the meeting bodies is to make a test case, as it were, in order to show clearly that the gravitative force of two such large bodies is sufficient to convert them both into a nebulous mass, besides throwing large portions of this mass into the attracting spheres of surrounding stars, and thus beyond the possibility of return. ”

“ As the two bodies approach conjunction, the small one will be drawn inward to meet the larger one, and this contraction of its orbit so increases its orbital velocity that, at the time of meeting, this velocity is greater than that of the controlling mass, and on striking it will give the latter an impulse to rotate in the direction of its orbital motion ”

“ For, while it is seemingly wasting its life-giving power in this struggle with resistance, it may, in reality, be storing up a new supply of potential energy, by which a future activity may be insured. ”

“ 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. ”