PHYSICAL ASTRONOMY. 339 



Thus it is found, that the laws of motion, and the ge- 

 neral properties of matter, are the same in the Hea- 

 vens and on the Earth ; that the elliptical motions 

 of the planets, both primary and secondary; the 

 small deviations from those motions, whether in the 

 places of the planets, or in the form and position of 

 their orbits ; the facts which concern their figures, 

 their rotation, and the position of their axis ; and, 

 lastly, the oscillation of the waters which surround 

 the Earth, are all explained by one principle^ 

 That of the mutual Gravitation of all Bodies, with 

 forces directly as their quantities of matter, and in- 

 versely as the squares of their distances. The exis- 

 tence of this force, it should be observed, was not 

 assumed as an hypothesis, but was deduced as a ne- 

 cessary consequence from the general facts or laws 

 discovered by KEPLER. 



We have thus arrived at the knowledge of a principle 

 which pervades all Nature, and connects together 

 the most distant regions of space, as well as the most 

 remote periods of duration. It is a principle also of 

 singular simplicity. Spherical bodies, made up of 

 particles, attracting according to this law, attract 

 one another according to the same, which could not 

 happen, if the attraction of the particles decreased 



in 



