SECT. III. STABILITY OF SYSTEM. 21 



position of their orbits, while the orbits of the lesser might 

 undergo unlimited changes. M. Le Verrier has applied this to the 

 solar system, and has found that the orbits of all the larger 

 planets will for ever maintain an unalterable stability in form 

 and position ; for, though liable to mutations of very long periods, 

 they return again exactly to what they originally were, oscillat- 

 ing between very narrow limits ; but he found a zone of instability 

 between the orbit of Mars, and twice the mean distance of the 

 earth from the sun,* or between 1'5 and 2-00 ; therefore the posi- 

 tion and form of the orbits of such of the telescopic planets as 

 revolve within that zone will be subject to unlimited variations. 

 But the orbits of those more remote from the sun than Flora , or 

 beyond 2*20, will be stable, so that their excentricities and incli- 

 nations must always have been, and will always remain, very 

 great, since they must have depended upon the primitive con- 

 ditions that prevailed when these planetary atoms were launched 

 into space. The 51st of these small bodies, which was discovered, 

 and the elements of its orbit determined, by M. Valz, at Nimes, 

 has a mean distance of 1*88 ; so it revolves within the zone 

 of instability. It has a shorter periodic time than any of 

 those previously discovered, and a greater excentricity, with the 

 exception of Nysa. Its orbit cuts that of Mars, and comes 

 nearer to the earth than the orbits of either Mars or Venus, 

 a circumstance which would be favourable for correcting 

 the parallax of the sun, or confirming its accuracy. The 

 telescopic planets, numerous as they are, have no influence 

 on the motions of the larger planets, for Jupiter has a diameter 

 of 90,734 miles, while that of Pallas, his nearest neighbour, is 

 only 97 miles, little more than the distance from London to 

 Bath. The diameter of Mars, on the other side of the small 

 planets, is 4546 miles, and that of the earth 7925 miles, so that 

 the telescopic group are too minute to disturb the others. M. 

 Le Verrier found another zone of instability between Venus and 

 the sun, on the border of which Mercury is revolving, the inclina- 

 tion of whose orbit to the plane of the ecliptic is about 7, which 

 is more than that of any of the large planets. Neptune's 



* The mean distance of the earth from the sun is 95,000,000 miles, 

 but to avoid the inconvenience of large numbers, it is assumed to be the 

 unit of distance; hence the mean distance of Mars is 1*52369, or 1'5 

 nearly, that of the earth being = 1. 



