pass forever away not only from himself but from the solar system, the earth, even in the full energy of her sun-like condition, could not probably have expelled bodies from her interior with velocity sufficing to carry them beyond the control of the sun.[1] The bodies ejected with velocities freeing them from the earth would thenceforward travel around the sun on orbits of different dimensions within certain limits.[2] Their orbits would at first intersect the earth's path, and, even under the perturbing actions of the planets, would always pass very near it, oscillating, in this respect, on either side of the earth's track so as at intervals to cross it for a while as at first. Hence there would always remain a chance of recapture, and indeed there would be a certainty that, in the fullness of time, every body ejected from the earth would be recaptured, though the fullness of time might in some cases mean many millions of years. Thus the capture of sporadic meteors of terrestrial origin would be fully accounted for.
In like manner with those streams of meteors whose orbits lie within the solar system so as to preclude the supposition that these bodies could have reached the system from without. I say definitely that the supposition is precluded, because the argument from the consideration of the laws of motion, by which I have shown that the giant planets could not possibly have captured these meteor-streams in the manner imagined by Schiaparelli, is admitted to be sound even by those who have not weighed my own theory in explanation of the origin of these systems. It is suggested by some, as by Professor Young, that there may be some way of explaining away the difficulty I have indicated; but I am not prepared to regard a vague suggestion of this kind as having any present weight. It seems, to say the truth, much as though one should say, for example, It has indeed been demonstrated mathematically that the circumference of a circle is not arithmetically commensurable with the diameter, but there may be
- ↑ It would not be absolutely impossible that some of the matter ejected from the earth in this way would pass away even from the solar system. It appears from the very existence of earth-ejected meteors, which we regard as demonstrated by Tschermak and Meunier, that she had power of ejecting matter with velocities up to seven miles per second. A velocity of little more than eight miles per second would suffice to carry matter away from the solar system if the matter chanced to be ejected from the middle of the advancing face of the earth, for then there would result relatively to the sun a velocity of more than twenty-six miles per second, which at the earth's distance is a velocity corresponding to parabolic motion around the sun; but this would very rarely happen.
- ↑ If we suppose our earth's eruptive power to be unable to give greater velocity of ejection than eight miles per second, then the velocities of bodies expelled from the earth would, at the distance from the sun where they began their independent careers, range between twenty-six miles and ten miles per second, the earth's orbital velocity being eighteen miles per second. Hence the orbits of the expelled bodies around the sun would range between parabolic orbits with perihelia at the earth's distance, and ellipitical orbits with aphelia at the earth's distance and perihelia at a distance of one third the earth's, with an eccentricity of ·866. None of the expelled bodies could come nearer to the sun than this last-named perihelion distance.
