260 NATURAL THEOLOaY. 



at first sent round in exact circular orbits, they could not 

 have kept them ; and if the law of attraction had not been 

 what it is, or at least, if the prevailing law had transgressed 

 the limits above assigned, every evagation would have been 

 fatal : the planet once drawn, as drawn it necessarily must 

 have been, out of its course, would have wandered in end- 

 less error. 



(*) V. "What we have seen in the law of the centripetal 

 force, namely, a choice guided by views of utility, and a 

 choice of one law out of thousands which might equally 

 have taken place, we see no less in the figures of the plan- 

 etary orbits. It was not enough to fix the law of the cen 

 tripetal force, though by the wisest choice ; for even under 

 that law, it was still competent to the planets to have moved 

 in paths possessing so great a degree of eccentricity as, in 

 the course of every revolution, to be brought very near to 

 the sun, and carried away to immense distances from him. 

 The comets actually move in orbits of this sort ; and had 

 the planets done so, instead of going round in orbits nearly 

 circular, the change from one extremity of temperature to 

 another must, in ours at least, have destroyed every animal 

 and plant upon its surface. Now, the distance from the 

 centre at which a planet sets cIT and the absolute force of at- 

 traction at that distance being fixed, the figure of its orbit — 

 it being a circle, or nearer to, or further off from a circle, 

 namely, 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 limits. 

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

 direction, will produce a peifect 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 circular ; that is, ellipses with small eccentrici- 

 ties. The velocity and the direction must both be right. If 

 the velocity be wrong, no direction will cure the error ; if 



