i88 



GENERAL SCIENCE 



of the hill, the engine must exert a continuous force equal 

 to XA- of the combined resistance of the train of cars. 



RAILROAD GRADE WHERE ENGINES ARE USED ON BOTH ENDS OF A TRAIN 



When building railroads and highways the grades are 

 made very gradual wherever possible, because it requires 

 much more work to pull a loaded wagon or train of cars 

 up a steep grade than up a gradual one of the same length. 

 125. The Wedge is only a modified inclined plane. 

 Some kinds consist of a simple inclined 

 plane with a base and slope, and others 

 consist of two inclined planes laid with 

 the bases together and the slopes on 

 either side. Wedges are used in split- 

 ting logs and stone, raising heavy 

 weights and buildings a short dis- 

 tance, launching ships, and similar 

 operations. 



Chisels, axes, knives, and tools used for cutting are 

 examples of wedges. The common pin is a wedge that 



SHOWING THE USE OF 

 THE WEDGE 



