64 :mechanics. 



may discover precisely how much strength is lost in draw- 

 ing heavy wagons up hill. If the load and wagon weigh 

 a ton, and the road rise one foot in height to every five 

 feet of distance, then the increased strength required to 

 draw the load Avill be one-fifth of its weight, or equal to 

 400 pounds. If it rise only one foot in twenty, then the 

 increase in power needed to ascend this plane will be only 

 100 i^ounds. The great importance of preserving, as 

 nearly as practicable, a perfect level is obvious. 



There are many roads made in this country, rising over 

 and descending hills, which might bo made nearly level by 

 deviating a little to the right or to the left. Suppose, for 

 example, that a road be required to connect the two points 



Fiff. 69. 



^^ Sm/^f 



a and h (fig. 69), three miles apart, but separated by a 

 lofty hill midway between them, and one mile in diameter. 

 Passing half a mile on either side would entirely avoid 

 the hill, and the road thus curved would be only one 

 hundred and forty-eight yards, or one-twelfth of a mile 

 longer. The same steep hill is ascended perhaps fifty to 

 five hundred times a year l)y a hundred difi*erent farmers, 

 expending an amount of strength, in the aggregate, 

 sufficient to elevate ten thousand tons annually to this 

 height, as a calculation will at once show more than 

 enough for all the increased expense of making the road 

 level. 



It is interesting and important to examine how much 

 further it is expedient to carry a road through a circuitous 

 level course than over a hill. To ascertain this point, we 

 must take into view the resistance occasioned by the rough 

 surface or soft material of the road. Roads vary greatly 



