144 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Let two ivory balls of equal weight be suspended by 

 threads, as in the annexed figure ; if the former be then 

 drawn aside and suffered to fall against the latter, it will 

 drive it to a distance equal to that through which the first 

 ball fell ; but it will itself rest, having given up all its own 

 moving power to the second ball. 



If five ivory balls, of equal weight, be hung by threads 

 of the same length, and the ball A be drawn out from the 

 perpendicular, and then let fall against the second, that and 

 the other two will continue stationary ; but the last ball, 

 B, will fly off the same distance as that through which the 

 first ball fell. For when the first ball strikes the second, it 

 receives a blow in return, which destroys its motion. The 

 second ball, although it does not appear to move, strikes 

 against the third, the reaction of which sets it at rest : the 

 action of the third ball is destroyed b} 7 the reaction of the 

 fourth, and so on, till motion is communicated to the last 

 ball, which, not being reacted upon, flies off. Therefore, 

 when one body strikes against another, the quantity of mo- 

 tion communicated to the second body is lost by the first, 

 but this loss proceeds not from the blow given by the 

 striking body but from the reaction of the body which it 

 struck. 



Price, set of 5, inch ivory balls, $1.25. 



5, 1 " " " $2.00. 



5, li " " " $3.00. 



5, li " " " $4.50. 



" mounted on mahogany frame 



with graduated arch, $7.00 to $12.00. 

 " set of 5, li inch boxwood 

 balls, on mahogany 

 frame, with arch, $3.50 to $7.00. 



" set of 5, li inch boxwood balls, $1.00. 



Machine for showing the Composition of Forces. Composi- 

 tion of forces is the finding the quantity and direction of a 

 single force, which is equivalent to two or more forces, act- 

 ing each differently, and of which the quantity and direction 

 are given. This machine (Fig. 151, next page) will prove 

 how two forces will conspire to produce one motion, and 

 that intermediate between them. 



At bottom is a square frame or table ; at one corner rises 

 a slender rod, and on each side of it an upright wire, bear- 



