ASTRONOMY. 2Gl 



ihe direction be in any considerable degree oblique, no veloc- 

 ity 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 degrees of 

 velocity, swift and slow, with v/hich a ball might be shot 

 ofi' none would answer the purpose of Mdiicli we are speak- 

 ing but what was nearly that of five miles in a second. II 

 it were less than that, the body would not get round at all, 

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

 ble degree more than that, the body would take one of those 

 eccentric courses, those long ellipses, of which we have no- 

 ticed the inconveniency. If the velocity reached the rate of 

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

 fly ofl' from the earth and never be heard of more. In like 

 manner with respect to the direction : out of the innumer- 

 able angles in wdiich the ball might be sent ofi^ — I mean 

 angles formed with a line drawn to the centre — none would 

 serve but what was nearly a right one. Out of the various 

 directions in which the cannon might be pointed, upwards 

 and downwards, every one would fail but what was exactly 

 or nearly horizontal. The same thing holds true of the 

 planets ; of our own among the rest. We are entitled there- 

 fore to ask, and to urge the question, Why did the projectile 

 velocity and projectile direction of the earth happen to be 

 nearly those which would retain it in a circular form ? Why 

 not one of the infinite number of velocities, one of the infi- 

 nite number of directions, which would have made it ap- 

 proach much nearer to, or recede much further from the 

 sun ? 



The planets going round, all in the same direction, and 

 all nearly in the same plane, afibrded to Bufibn a ground for 

 asserting, that they had all been shivered from the sun by 

 the same stroke of a comet, and by that stroke projected into 

 their present orbits. Now, besides that this is to attribute 

 to chance the fortunate concurrence of velocity and direction 

 which we have been here noticing, the hypothesis, oa I ap 



