PT. T. Astronomy and Geology compared. 35 



transits can be foretold with the same precision as 

 that with which we calculate the eclipses of our 

 own Moon. This shows that in 105 years not the 

 slightest change takes place in the revolutions of 

 either. 



Many other illustrations might be afforded in. 

 proof of the foregoing facts, establishing the per- 

 fect uniformity and exact periodical recurrence of 

 all the motions of the bodies composing the Solar 

 System, governed as they are by the universal law 

 of gravitation. Indeed, there is no part of that 

 system which does not corroborate the truth of these 

 principles. Wherever slight disturbances have been 

 discovered, they have been found to result from the 

 effects of the law of gravitation acting by the dif- 

 ferent planets upon each other, and therefore slightly 

 modifying the force of gravitation exercised by the 

 Sun itself. These were first traced by Laplace, but 

 they always furnished, upon examination, a corrobo- 

 ration of the proof of the great principles upon 

 which the Solar System rests. The last instance of 

 this kind is to be found in the simultaneous dis- 

 covery of the planet Neptune by our own country- 

 man Mr. Adams, and by M. Le Verrier, deduced 

 from the observation of slight irregularities in the 

 D 2 



