5 6 THE POPULAR SCIENCE MONTHLY. 



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.* The bodies ejected 

 with velocities freeing them from the earth would thenceforward travel 

 around the sun on orbits of different dimensions within certain limits.f 

 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 ter- 

 restrial 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 con- 

 sideration 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 sugges- 

 tion 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 sec- 

 ond. 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 corre- 

 sponding to parabolic motion around the sun; but this would very rarely happen. 



t 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. 



