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



wheel, two, five, and ten inches, also having a number of 

 spokes, or handles, on the circumference. 



The levers are conveniently arranged on a separate stand, 

 the principal one being arranged for explaining the balance. 



The inclined plane and wedge are mounted also on a 

 separate stand. 



The screw has a brass spiral, mounted in the same frame, 

 for conveniently explaining this power. 



A set of brass weights accompany the set, from twenty 

 ounces down to one quarter of an ounce. 



There is also added an apparatus for the showing the 

 composition and resolution of forces. 



The frames are made uniform, and the three first instru- 

 ments are about three feet high, the brass work highly 

 finished, and the wood work well polished, forming an 

 imposing apparatus. 



Price, for the whole, mounted on four frames, $60.00. 



The Pulleys. Two equal weights suspended to the ends 

 of a string that goes over a fixed pulley, will balance each 

 other, for they are equally stretched by the weights, and if 

 either of them be pulled down through any given space, the 

 other will rise through an equal space in the same time ; 

 and, consequently, as the velocity and the weights are equal 

 they must balance. 



Though this pulley gives no mechanical advantage, it is a 

 source of great convenience, as it takes off the necessity a 

 man would be otherwise under of ascending along with the 

 weight, and thus lessens his labor; besides having this 

 further convenience, that by means thereof the joint strength 

 of several persons may be made use of to raise the same 

 weight. Either of the two first pulleys, A, in this set (Fig. 

 159) may be used to illustrate this arrangement, in which 

 case the movable pulley represented in the plate is discon- 

 nected. 



B. The Movable Pulley in this arrangement has a weight 

 hanging at the lower end, and one end of the cord going 

 round the pulley, is fastened to a hook in the lower part of 

 the fixed pulley above, while the other end goes over the 

 fixed pulley, and is sustained by the weight. The two cords 

 support the whole weight, each supporting one half ; what- 

 ever holds the upper end of either rope, sustains one half 

 the weight. If you take hold of the cord and pull upwards 



