MOTION, MECHANICS, ETC. 109 



planets would carry them quite off, and the sun with them ; 

 especially when several of them happened to be in any one 

 quarter of the heavens. For the sun and planets are as 

 much connected by the mutual attraction that subsists be- 

 tween them, as the bodies A and B are by the wire C, which 

 is fixed into them both. And even if there were but one 

 single planet in the whole heavens to go round ever so large 

 a sun in the centre of its orbit, its centrifugal force would 

 soon carry off both itself and the sun. For, the greatest 

 body placed in any part of free space might be easily moved ; 

 because, if there were no other body to attract it, it could 

 have no weight or gravity of itself; and consequently, 

 though it could have no tendency of itself to remove from 

 that part of space, yet it might be very easily moved by 

 any other substance. 



10. As the centrifugal force of the light body, B, will 

 not allow the heavy body, A, to remain in the centre of 

 motion, even though it is twenty-four times as heavy as B ; 

 let us now take the ball, A (Fig. 172), which weighs six 

 ounces, and connect it by the wire, 

 C, with the ball, B, which weighs 

 only one ounce ; and let the fork, E, 

 l>e fixed in the centre of the whirl- 

 ing-board ; then hang the balls upon 

 the fork by the wire, C, in such 

 manner, that they may exactly ba- 

 lance each other ; which will be 

 when the centre of gravity between 

 them, in the wire at d, is supported 

 by the fork. And this centre of 

 gravity is as much nearer to the 

 centre of the ball, A, than to the centre of the ball, B, as 

 A is heavier than B, allowing for the weight of the wire 

 on each side of the fork. This done, let the machine be 

 put into motion by the winch ; and the balls, A and B, will 

 go round their common centre of gravity, d, keeping their 

 balance, because either will not allow the other to fly off with 

 it. For, supposing the ball, B, to weigh only one ounce, and 

 the ball, A, to be six ounces ; then, if the wire, C, were 

 equally heavy on each side of the fork, the centre of gravity, 

 d, would be six times as far from the centre of the ball, B, 

 as from that of the ball, A, and, consequently, B will revolve 

 with a velocity six times as great as A does ; which will 



