196 THE POPULAR SCIENCE MONTHLY. 



Olbers's discovery, on the 28th of March, 1802, of a second 

 planet, Pallas, revolving around the sun at the same mean dis- 

 tance as Ceres, presented the question under a new aspect. Gauss's 

 calculation showed that Ceres and Pallas might, in time, come to 

 pass very near each other on the line of intersection described 

 as A B of the planes of their several orbits. Olbers was thus 

 led to think that the two little bodies might be fragments of a 

 greater planet which had been broken up by an internal commo- 

 tion. If this were the case, there would probably be other frag- 

 ments, the orbits of which would pass the line A B, so that by 

 watching the two points A and B, where this line strikes the 

 celestial sphere, chances might occur of seeing the fragments of 

 the primitive planet pass. Eventually Harding found Juno near 

 A in 1804, and Olbers discovered Vesta near B in 1807. 



Further researches, carried on by Olbers till 1816, brought no 

 result ; and it was not till 1845 that a fifth body, still smaller than 

 the other four, was discovered by Encke. After this time, dis- 

 coveries became frequent and regular, till now 299 are known.* 

 But the size of the new stars keeps getting smaller : the first four 

 were between the sixth and the eighth magnitudes ; the two dis- 

 covered by Encke were of the ninth ; and those which are now 

 discovered from time to time seldom exceed the thirteenth mag- 

 nitude. William Herschel, in consideration of the small size of 

 these bodies, and hardly regarding them as sufficient to fill the 

 place of a planet, thought it more fitting to call them asteroids 

 than planets. 



- A survey of the orbits of the asteroids as a whole will help us 

 to gain clearer ideas respecting them, and may bring out a few 

 simple relations that will cast some light on the origin of the bod- 

 ies. The supposition of Olbers is not sustained. Prof. Newcomb, 

 having studied the orbits of the first forty asteroids, found that, 

 as they move to-day, they are far from passing in the same line. 

 Even the hypothesis that the geometrical condition supposed may 

 once have existed, but has been changed by the perturbations 

 caused by the attractions of the other planets, is contradicted by 

 the calculations. 



But this hypothesis, though it must be abandoned, has the 

 credit of having provoked the discovery of Juno and Vesta, and of 

 having suggested Lagrange's theory of the origin of comets, to 

 which M. Faye has added a number of curious speculations, and 

 by the aid of which we may, perhaps, some day find an expla- 

 nation of the origin of meteors. The smallest mean distance 

 from the sun of the known asteroids, 149, is 2'13 (times the mean 

 distance of the earth) ; the greatest, that of 279, 4*26 ; the corre- 



* Since increased to 308. 



