286 



THE INCLINED PLANE, WEDGE, AND SCREW. 



effects will ensue, draw the lines W D and W 7 D 7 in the vertical direction, and 

 take upon them as many inches as there are ounces in the weights respectively. 

 W D and W 7 D' being the lengths thus taken, and therefore representing the 

 weights, the lines W E and W 7 E x will represent the effects of these weights 

 respectively down the planes. If W E and W 7 E 7 be equal, the weights will 

 sustain each other without motion. But if WE be greater than W 7 E 7 , the 

 weight W will descend, drawing the weight W 7 up. And if W 7 E 7 be greater 

 than W E, the weight W 7 will descend, drawing the weight W up. In every 

 case, the lines W F and W 7 F 7 will represent the pressures upon the planes 

 respectively. 



It is not necessary for the effect just described, that the inclined planes 

 should, as represented in the figure, form an angle with each other. They 

 may be parallel, or in any other position, the rope being carried over a suffi- 

 cient number of wheels placed so as to give it the necessary deflection. This 

 method of moving loads is frequently applied in great public works where rail- 

 roads are used. Loaded wagons descend one inclined plane, while other 

 wagons, either empty or so loaded as to permit the descent of those with which 

 they are connected, are drawn up the other. 



In the application of the inclined plane, which we have hitherto noticed, 

 the machine itself is supposed to be fixed in its position, while the weight or 

 load is moved upon it. But it frequently happens that resistances are to be 

 overcome which do not admit to be thus moved. In such cases, instead of 

 moving the load upon the plane, the plane is to be moved under or against the 

 load. Let D E, fig. 3, be a heavy beam secured in a vertical position be- 



Fig. 3. 



tween guides, F G and H I, so that it is free to move upward or downward, 

 but not laterally. Let A B C be an inclined plane, the extremity of which is 

 placed beneath the end of the beam. A force applied to the back of this plane 

 A C, in the direction C B, will urge the plane under the beam, so as to raise 

 the beam to the position represented in fig. 4. Thus, while the inclined plane 

 is moved through the distance C B, the beam is raised through the height C A. 



Fig. 4. 



