190 EXPERIMENTAL GENERAL SCIENCE 



one end of a rope be fastened to a support, however, and then 

 carried over a free pulley to which a weight is attached, a 

 pull upward of 25 pounds will lift a 50-pound weight, but the 

 rope will move twice as far as the weight is lifted. The power 

 or effort necessary to move a given weight by the use of a 

 pulley may therefore be diminished by introducing one or 

 more free pulleys over which the rope runs. In other words 

 the power is multiplied as many times as the rope passes over 

 the movable pulley, or pulleys thus introduced. The distance 

 through which the rope must move, however, is also multi- 

 plied in proportion to the distance traversed by the weight 

 lifted. 



156. The Inclined Plane and Its Adaptations. The second 

 type of the simple machine is the inclined plane. In this the 

 mechanical advantage is the ratio of the length of the plane 

 to its height. For instance, it will take only one-half as much 

 effort to roll a barrel up a plane 8 feet long into a wagon 4 

 feet high, as it would to lift the barrel directly into the wagon, 

 but though the force in this instance is only half as great, it 

 travels twice as far. The wedge is a form of the inclined plane 

 which is pushed under the load instead of the load being moved 

 upon it. Its mechanical advantage is exactly like that of the 

 inclined plane. The screw may be regarded as an inclined 

 plane winding about a cylinder. The distance between any 

 two adjoining threads is called the pitch. Screws when used 

 as machines, usually work with a lever. The mechanical 

 advantage in the screw is found to be the ratio of the distance 

 traveled by the power (end of the lever) to the pitch of the 

 screw. If the pitch is Y inch and the lever travels in a circle 

 3 feet in circumference, the ration would be 144 (3 X 12 X 4) 

 to 1, and a force of 10 pounds applied on the lever would lift 

 a weight of 1440 pounds on the screw. 



157. The Hydraulic Press. The hydraulic press is a 

 machine by means of which a man is able to exert many 



