42 FERGUSON'S LECTURES. 



the whirling-board of the machine, so that their centers 

 may coincide ; if then the board be turned ever so quick 

 by the winch, the demi-globe will remain where it was 

 placed. But if the wire C be screwed into the demi-globe 

 at d, thewhole becomes one body, whose center of gravity 

 is now at or near d. Let the pin c be fixed in the center of 

 the whirling-board, and the deep groove b cut in the flat 

 side of the demi-globe be put upon the 

 pin, so as the pin may be in the center of 

 A, and let the whirlkig-board be turned A / 

 by the winch, which will carry the little 

 ball B M with its wire C, and the demi- 

 globe A, all round the center-pin c i; and 

 then, the centrifugal force of the little ball jB, which 

 weighs only one ounce, will be so great, as to draw 

 off the demi-globe A, which weighs two pounds, until 

 the end of the groove at e strikes against the pin c, 

 and so prevents the demi-globe A from going any 

 farther : otherwise, the centrifugal force of B would 

 have been great enough to have carried A quite off 

 the whirling-board. Which shews, that if the sun 

 were placed in the very center of the orbits of the 

 planets, it could not possibly remain there ; for the 

 centrifugal forces of the 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 between 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 center 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 



Note 26. See Engraving, page 41. 



