36 FERGUSON'S LECTURES. 



the ball will continue to revolve for some time upon the 

 board ; but as the friction gradually stops its motion, 

 the weight acting upon it will bring it nearer and nearer 

 to the center in every revolution, until it brings it quite 

 thither. This shews, that if the planets met with any 

 resistance in going round the sun, its attractive power 

 would bring them nearer and nearer to it in every revo- 

 mtion, until they fell upon it. 

 Bodies 3. Take hold of the cord below the machine with one 



IDOVC 



faster in hand, and with the other throw the ball upon the round 



n board as ^ were at riglit angles to the cord, by which 

 in large means it will go round and round upon the board. Then 

 observing with what velocity it moves, pull the cord 

 below the machine, which will bring the ball nearer to 

 the center of the board, and you will see the nearer the 

 ball is drawn to the center, the faster it will revolve ; as 

 those planets which are nearest the sun revolve faster 

 than those which are more remote ; and not only go 

 round sooner, because they describe smaller circles, but 

 even move faster in every part of their respective circles. 

 Their cen- 4. Take away this ball, and apply the bearer MX, 



trifugal 



forces whose center of motion is in its middle at w, directly 



shewn. oyer j.j le cen t er o f ^ e whirling-board d. Then put two 

 balls ( V and V) of equal weights upon their bearing- 

 wires, and having fixed them at equal distances from their 

 respective centers of motion w and x upon their silk 

 cords, by the screw nuts, put equal weights in the 

 towers O and P. Lastly, put the catgut strings E and 

 .Fupon the grooves G and H of the small wheels, which 

 being of equal diameters, will give equal velocities to 

 the bearers above, when the winch B is turned : and 



trating the centrifugal [motion of a revolving body. It consists in 

 filling a small pail with water, and it will be found, that the vessel 

 may be made to revolve without any portion of the water being spilt. 

 In all cases however, the velocity must be such, that the centrifugal 

 force exceeds that of the gravitating force, otherwise the pail would 

 discharge its contents when first inverted. 



