230 



ASTRONOMY. 



the velocity reached at 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 direction; out of the innumerable angles in which 

 the ball might be sent off, 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 hori- 

 zontal. The same thing holds true of the planets; of our 

 own among the rest. We are entitled, therefore, to ask 

 and to urge the question, Why did the projectile velocity, 

 and the projectile direction of the earth happen to be near- 

 ly those wliich would retain it in a circular form ? Why 

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

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

 proach much nearer to, or recede much farther from, the 

 sun? 



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

 all nearly in the same plane, afforded to Buffon a ground 

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

 by the same stroke of a comet, and by that stroke project- 

 ed into their present orbits. Now, beside that this is to 

 attribute to chance the fortunate concurrence of velocity 

 and direction which we have been here noticing, the hy- 

 pothesis, as I apprehend, is inconsistent with the physical 

 laws by which the heavenly motions are governed. If the 

 planets were struck off from the surface of the sun, they 

 would return to the surface of the sun again. Nor will 

 this difficulty be got rid of, by supposing that the same vio- 

 lent blow which shattered the sun's surface, and separated 

 large fragments from it, pushed the sun himself out of his 

 place ; for the consequence of this would be, that the sun 

 ■and system of shattered fragments would have a progres- 

 sive motion, which, indeed, may possibly be the case 

 with our system ; but then each fragment would, in ev- 

 ery revolution, return to the surface of the sun again. The 

 hypothesis is also contradicted by the vast difference which 



fall down on the other. Now it will be seen that the curves at B, C, 

 and D, make the angles ABI, ACI, ADI less, as the body is supposed 

 to go farther and farther before it falls, and that the curves in which the 

 body can complete a revolution near the surface, will, in all its parts, be 

 nearly parallel to it. Hence, the cannon ball fired upwards will come 

 back again to the ground; and not be able completely to go round the 

 earth upon any other supposition, excepting that of its being fired ia 

 nearly an horizontal direction. Paxton. 



