GRAVITY, WEIGHT, &C. $9 



same point, and agree in quantity : that, if the 

 Moon were to approach to ihe surface of the 

 E th, the force, by which it is retained in its or- 

 bit, would make it descend ,waids .he centre of 

 the Earth, through ihe same space which a heavy 

 body, falling by its gravity, would descend through 

 in the same time : and that if a stone or a bullet 

 could be carried to the distance of the Moon, and 

 there projected with a sufficient velocity, it would 

 revolve round the Earth like a Moon, for the same 

 reason by which it is bent into a curve, when pro- 

 jected near the surface of the earth. By pursuing 

 these methods Sir Isaac Newton demonstrated the 

 universal gravitation of matter ; and it is now 

 pretty generally allowed that the same principle of 

 gravity, by which we see all bodies tend towards 

 the centre of the Earth, is a general law of na- 

 ture, extended to all distances, and to every body 

 in the universe. Thus it is agreed, that the pri- 

 mary and secondary planets in our system, as also 

 the Sun, are mutually attracted by each other. 

 But since all attractions are mutual, it will follow, 

 that if one or more bodies revolve about another, 

 which is also attracted by them, that other body will 

 not be at rest ; but together with them will revolve 

 round the common centre of gravity of the whole 

 system. Hence, then, and from the proportions of 

 the quantities of matter of the Sun and the planets, 

 it is found that the common centre of gravity of 

 {he solar system is never far removed from the body 

 of the Sun, and is generally within its surface. 

 Round this point the Sun itself is continually, 



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