1G4 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



the winch ; then the ball will go round and round with the 

 board, and will gradually fly off further and further from the 

 centre, and raise up the weight below the machine ; which 

 shows, that all bodies revolving in circles have a tendency 

 to fly off from these circles, and must have some power 

 acting upon them from the centre of motion, to keep them 

 from flying off. Stop the machine, and the ball will con- 

 tinue 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 centre in every revo- 

 lution, until it brings it quite thither. This shows, 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 revolution, until they fell upon it. 



3. Bodies move faster in small orbits than in large ones. 

 Take hold of the cord below the machine with one hand, 

 and with the other throw the ball upon the round board as 

 it were at right angles to the cord, by which 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 centre of the board, 

 and you will see, that the nearer the ball is drawn to the 

 centre, the faster it will revolve ; as those planets which are 

 nearer the sun revolve faster than those which are more re- 

 mote ; and not only go round sooner, because they describe 

 smaller circles, but even move faster in every part of their 

 respective circles. 



4. Their centrifugal forces shown. Take away this ball, 

 and apply the bearer, M X, whose centre of motion is in its 

 middle at w. Then put two balls, Y and U, of equal weights 

 upon their bearing wires, and having fixed them at equal 

 distances from their respective centres of motion, w and x, 

 upon their silk cords, by the screw nuts, put equal weights 

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

 and F, upon 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 the 

 balls, U and V, will fly off towards M and N ; and will 

 raise the weights in the towers at the same instant. This 

 shows, that when bodies of equal quantities of matter revolve 

 in equal circles with equal velocities, their centrifugal forces 

 are equal. 



5. Take away these equal balls, and instead of them put 



