300 HOW MACHINES LIGHTEN LABOR 



The slope of the road is called its grade and the grade itself 

 is simply the number of feet the hill rises per mile. A road 

 a mile long (5280 feet) has a grade of 132 if the crest of the hill 

 is 132 feet above the level at which the road started. 



In such an incline, the ratio of length to height is 5280 -f- 132, 

 or 40. Hence in order to pull a train of cars to the summit, 

 the engine would need to exert a continuous pull equal to 

 one fortieth of the combined weight of the train. 



FIG. 1 66. A long, gradual ascent is better than a shorter, steeper one. 



If, on the other hand, the ascent had been gradual, so that 

 the grade was 66 feet per mile, a pull from the engine of one 

 eightieth of the combined weight would have sufficed. 



Because of these facts, engineers spend large sums of money 

 in grading down railroad beds and in making them as nearly 

 level as possible. In mountainous regions where the land can- 

 not be leveled, the railroad winds around the mountain in a 

 long gradual ascento 



