NATURAL THEOLOGY, 41 



a circle, viz. a rounder or a longer oval, depends 

 upon two things, the velocity with which, and the 

 direction in which, the planet is projected. And 

 these, in order to produce a right result, must be 

 both brought within certain narrow Umits. One, 

 and only one, velocity, united with one, and only 

 one, direction, will produce a perfect circle. And 

 the velocity must be near to this velocity, and the 

 direction also near to this direction, to produce 

 orbits, such as the planetary orbits are, nearly cir- 

 cular ; that is, ellipses with small eccentricities. 

 The velocity and the direction must both be right. 

 If the velocity be wrong, no direction will cure 

 the error; if the direction be in any considerable 

 degree oblique, no velocity will produce the orbit 

 required. Take for example, the attraction of 

 gravity at the surface of the earth. The force of 

 that attraction being what it is, out of all the de- 

 grees of velocity, swift and slow, with which a ball 

 might be shot off, none would answer the purpose 

 of which we are speaking, but what was nearly 

 that of five miles in a second. If it were less than 

 that, the body would not get round at all, but 

 would come to the ground ; if it were in any con- 

 siderable degree more than that, the body would 

 take one of those eccentric courses, those long 

 elhpses, of which we have noticed the inconveni- 

 ency. If the velocity reached the rate of seven 

 miles in a second, or went beyond that, the ball 

 would fly off from the earth, and never be heard 

 of more. In like manner with respect to the di- 

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