426 CONCLUSION. SECT. XXXVII. 



theory with observation. Thus all matter is pervious to gravita- 

 tion, and is equally attracted by it. 



Gravitation is a feeble force, vastly inferior to electric action, 

 chemical affinity, and cohesion ; yet, as far as human knowledge 

 extends, the intensity of gravitation has never varied within the 

 limits of the solar system; nor does even analogy lead us to 

 expect that it should : on the contrary, there is every reason to 

 be assured that the great laws of the universe are immutable, like 

 their Author. Nor can we suppose the structure of the globe 

 alone to be exempt from the universal fiat of general laws, though 

 ages may pass before the changes it has undergone, or that are 

 now in progress, can be referred to existing causes with the same 

 certainty with which the motions of the planets, and all their 

 periodic and secular variations, are referable to the law of gravi- 

 tation. The traces of extreme antiquity perpetually occurring to 

 the geologist give that information, as to the origin of things, in 

 vain looked for in the other parts of the universe. They date the 

 beginning of time with regard to our system, since there is ground 

 to believe that the formation of the earth was contemporaneous 

 with that of the rest of the planets ; but they show that creation 

 is the work of Him with whom " a thousand years are as one 

 day, and one day as a thousand years." 



In the work now brought to a conclusion, it has been necessary 

 to select from the whole circle of the sciences a few of the most 

 obvious of those proximate links which connect them together, 

 and to pass over innumerable cases both of evident and occult 

 alliance. Any one branch traced through its ramifications would 

 alone have occupied a volume ; it is hoped, nevertheless, that 

 the view here given will suffice to show the extent to which a 

 consideration of the reciprocal influence of even a few of these 

 subjects may ultimately lead. It thus appears that the theory 

 of dynamics, founded upon terrestrial phenomena, is indispensable 

 for acquiring a knowledge of the revolutions of the celestial 

 bodies and their reciprocal influences. The motions of the 

 satellites are affected by the forms of their primaries, and the 

 figures of the planets themselves depend upon their rotations. 

 The symmetry of their internal structure proves the stability of 

 these rotatory motions, and the immutability of the length of the 

 day, which furnishes an invariable standard of time ; and the 

 actual size of the terrestrial spheroid affords the means of ascer- 



