SECT. XXXVII. GENERAL LAWS. 425 



must have some influence on the nearest of them, as, for example, 

 a Centauri, which is only 20,602 times the radius of the earth's 

 orbit from the sun, while La Place has computed that the solar 

 gravitation extends a hundred millions of times farther than the 

 semidiameter of the terrestrial orbit. Possibly the star dust in 

 the Milky Way may be beyond, or on the verge of, that enormous 

 limit ; yet it is very unlikely that either the sun, or any of the stars 

 which form the great cluster to which we belong, should be 

 unconnected bodies. 



The curves in which the celestial bodies move by the force of 

 gravitation are only lines of the second order. The attraction of 

 spheroids, according to any other law of force than that of gravi- 

 tation, would be much more complicated ; and, as it is easy to 

 prove that matter might have been moved according to an infinite 

 variety of laws, it may be concluded that gravitation must have 

 been selected by Divine Wisdom out of an infinity of others, as 

 being the most simple, and that which gives the greatest stability 

 to the celestial motions. 



It is a singular result of the simplicity of the laws of nature, 

 which admit only of the observation and comparison of ratios, 

 that the gravitation and theory of the motions of the celestial 

 bodies are independent of their absolute magnitudes and distances. 

 Consequently, if all the bodies of the solar system, their mutual 

 distances, and their velocities, were to diminish proportionally, 

 they would describe curves in all respects similar to those in 

 which they now move ; and the system might be successively 

 reduced to the smallest sensible dimensions, and still exhibit the 

 same appearances. 



The action of the gravitating force is not impeded by the inter- 

 vention even of the densest substances. If the attraction of the 

 sun for the centre of the earth, and of the hemisphere diametri- 

 cally opposite to him, were diminished by a difficulty in penetrat- 

 ing 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 



