A RIXG OF WORLDS. 



i . 



tily the region might be disturbed. The very ac- 

 tivity of the disturbing forces might, in this case, 

 check the process of aggregation. . The two bod- 

 ies which had once come into collision would 

 travel on intersecting orbits, and would therefore 

 before long come into collision, if not perturbed ; 

 but if perturbed, their orbits would cease to 

 coalesce ; so that the action of a great disturb- 

 ing planet might prevent a process of aggrega- 

 tion which had already commenced. Now, we 

 know that the quantity of matter in the region 

 where the asteroids travel is less than in any 

 other zone of the solar system. We do not 

 know how many asteroids there are, but we do 

 know how much they all weigh ; at least, we 

 know that altogether their weight is not more 

 than a fourth of our earth's, and is probably a 

 great deal less. And the zone over which they 

 range is very much larger than the zone over 

 which our earth may be regarded as bearing 

 sway. Their zone being thus poverty-stricken, 

 and Jupiter's mighty mass in their neighborhood 

 perturbing them too actively to allow of their 

 aggregation, they remain as a ring of fragments. 

 And now let the signs of Jupiter's influence 

 in this respect be noticed. He would perturb all 

 these fragments pretty equally in a single revo- 

 lution of his. But those whose periods syn- 

 chronized with his own would be more seriously 

 perturbed. For the disturbance produced in one 

 set of revolutions which brought any asteroid 

 and Jupiter back to the position they had before 

 those revolutions began, would be renewed in the 

 next similar set, and in the next, and so on, un- 

 til one of two things happened. Either the as- 

 teroid would be thrown entirely out of that peri- 

 odic motion which had brought it thus under 

 Jupiter's effectively disturbing influence, or, being 

 set traveling on a markedly eccentric path, it 

 would be brought into collision with some of the 

 neighboring asteroids, and would cease to have 

 separate existence, or at least move thencefor- 

 ward on a changed orbit. Thus those asteroids 

 having a period synchronizing with that of Jupi- 

 ter would be gradually eliminated, and we should 

 find gaps in the ring of worlds precisely where 

 gaps actually exist. 



There can be no reasonable doubt that these 

 marked gaps were produced in the manner here 

 described. Their existence can indeed be ex- 

 plained in no other way, and can be so satisfac- 

 torily explained in this way that assurance is 

 made doubly sure. 



But now consider the significance of this re- 

 sult. Imagine the asteroidal ring as it now ex- 



ists to be redistributed, the gaps being filled up. 

 The process we have described would immedi- 

 ately come into operation. But many millions 

 of years would be required before it could elimi- 

 nate even a few among the asteroids having 

 those synchronous periods which expose them to 

 accumulating perturbations. Only one of the two 

 processes above described would really be effec- 

 tive. Mere change of period would be oscilla- 

 tory. We have an instance of the kind in the 

 motions of Jupiter and Saturn, which very nearly 

 synchronize, Saturn going almost exactly twice 

 round the sun while Jupiter goes five times 

 round. But, though for a long period of time 

 accumulating perturbations lengthen Saturn's 

 period (and shorten Jupiter's), after a while the 

 time comes when these changes are reversed ; 

 then Saturn's period begins to shorten (and Ju- 

 piter's to lengthen). The changes carry these 

 periods on either side of their mean value, just 

 as the swinging of a pendulum carries it on 

 either side of its mean position. So it would be 

 with an asteroid mightily perturbed by Jupiter : 

 its period would oscillate more widely, but still 

 it would oscillate ; and during the middle of the 

 oscillation (just as a pendulum at the middle of 

 its swing is in its mean position) the asteroid 

 would have that synchronous period which, as 

 we have seen, none of the asteroids in point of 

 fact possess. We must look, then, to collisions 

 to cause the gaps in the ring of worlds. But 

 how rare must such collisions be among minute 

 bodies like the asteroids, even though they be 

 hundreds of thousands in number, occupying a 

 domain in space so vast as that which belongs to 

 this system ! The width of the ring greatly ex- 

 ceeds the earth's distance from the sun, amount- 

 ing in fact to more than 120,000,000 miles. Its 

 innermost edge is more than 200,000,000 miles 

 from the sun. It is not a flat ring, but shaped 

 like an anchor-ring (or a wedding-ring), and is 

 as thick as it is wide — insomuch that a cross- 

 section of the ring would be a mighty circle, 

 more than 120,000,000 miles in diameter. Amid 

 this enormous space 1,000,000 asteroids, each 

 five hundred miles in diameter (and none of the 

 asteroids are so large, while the number even 

 of those exceeding one hundred miles in diam- 

 eter scarcely amounts to a hundred), would be 

 as widely scattered as 1,000,000 grains of sand 

 would be in such a space as the interior of St. 

 Peter's, at Rome. Take a cubical block of sand- 

 stone, one inch in length, breadth, and thick- 

 ness, crumble it into finest sand-dust, and imagine 

 this dust scattered in the interior of that great 



