STABILITY OF THE SYSTEM. 101 



approach perpetually nearer and nearer the earth 

 every revolution ; it is easy to see that in the one 

 case our year would change its character, as we 

 have noticed in the last section ; in the other, our 

 satellite might finally fall to the earth, which must 

 of course bring about a dreadful catastrophe. 

 If the positions of the planetary orbits, with re- 

 spect to that of the earth, were to change much, 

 the planets might sometimes come very near us, 

 and thus exaggerate the effects of their attraction 

 beyond calculable limits. Under such circum- 

 stances, we might have " years of unequal length, 

 and seasons of capricious temperature, planets and 

 moons of portentous size and aspect, glaring and 

 disappearing at uncertain intervals ;" tides like 

 deluges, sweeping over whole continents ; and, 

 perhaps, the collision of two of the planets, and 

 the consequent destruction of all organization on 

 both of them. 



Nor is it, on a common examination of the 

 history of the solar system, at all clear that there 

 is no tendency to indefinite derangement. The 

 fact really is, that changes are taking place in the 

 motions of the heavenly bodies, which have gone 

 on progressively from the first dawn of science. 

 The excentricity of the earth's orbit has been 

 diminishing from the earliest observations to our 

 times. The moon has been moving quicker and 

 quicker from the time of the first recorded 

 eclipses, and is now in advance, by about four 



w. 5 M 



