454 GRAVITATING FORCE. LSECT. xxxvm. 



diametrically opposite to him, were diminished by a difficulty 

 in penetrating the interposed matter, the tides would be 

 more obviously affected. Its attraction is the same also, 

 whatever the substances of the celestial bodies may be ; for, 

 if the action of the sun upon the earth differed by a millionth 

 part from his action upon the moon, the difference would 

 occasion a periodical variation in the moon's parallax, whose 

 maximum would be the -^ of a second, and also a variation 

 in her longitude amounting to several seconds a supposition 

 proved to be impossible, by the agreement of theory with 

 observation. Thus all matter is pervious to gravitation, 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. Not only the sun 

 and planets, but the minutest particles, in all the varieties of 

 their attractions and repulsions nay, even the imponderable 

 matter of the electric, galvanic, or magnetic fluid are all 

 obedient to permanent laws, though we may not be able, in 

 every case, to resolve their phenomena into general princi- 

 ples. Nor can we suppose the structure of the globe alone 

 to be exempt from the universal fiat, 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 gravitation. 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 forma- 

 tion of the earth was contemporaneous with that of the rest 



