8 THE BODIES OF SPACE, 



Of the forty-three motions ascertained in the early part of 

 this century, it was found by Laplace, that the adverse 

 chances were as upwards of four millions of millions to one. 

 It is thus powerfully impressed on us that the uniformity of 

 the motions, as well as their general adjustment to one plane, 

 must have been a consequence of a single cause acting through- 

 out the whole system. 



Some of the other relations of the bodies are not less re- 

 markable. It is, perhaps, of little consequence that the larger 

 planets are towards the outside of the system, since there is 

 an absence of regularity in the gradation in this respect. In 

 the series of comparative densities we find an approach to a 

 regular gradation : they stand thus in decimals, the Earth being 

 considered as 1 Mercury, 2*95 ; Venus, '99 ; Earth 1 ; 

 Mars, -79 ; Jupiter, -23 ; Saturn, -11 ; Uranus, -26 ; the last 

 being the only very decided violation of the rule. Then the 

 distances are curiously relative. It has been found that, if 

 we place the following line of numbers, 



03 6 12 24 48 96 192 

 and add 4 to each, we shall have a series denoting the re- 

 spective distances of the planets from the sun. It will stand 

 thus 



4 7 10 16 28 52 100 196 

 Merc. Venus. Earth. Mars. Jupiter. Saturn. Uranus. 



It will be observed that the first row of figures goes on from 

 the second on the left hand in a succession of duplications, or 

 multiplications by 2. Surely there is here a most surprising 

 proof of unity in the solar system. It was remarked, when 

 this relation was first detected, that there was the want of a 

 planet corresponding to 28 ; the difficulty was afterwards 

 considered as overcome, by the discovery of four small planets 

 revolving at nearly one mean distance from the sun, between 

 Mars and Jupiter.( 5 ) The distances bear an equally interest- 

 ing mathematical relation to the times of the revolutions 

 round the sun. With respect to any two planets, the squares of 

 the times of revolutions are to each other in the same propor- 

 tion as the cubes of their mean distances, a most surprising 

 result, for the discovery of which the world was indebted to 



