286 Elementary Principles of Agriculture 



Other results have shown that to draw a ton on hard, 

 ^mooth macadam road required 45 pounds pull, on hard 

 rolled gravel road 75 pounds, and on earth roads 224 

 pounds. It will thus be seen that a good road-bed 

 enables a horse to draw from two to five times as much 

 on level roads as on rough roads. 



406. How the Grade Affects the Draft. In improving 

 roads, it is very important that the steep hills be avoided 

 by cutting down at top and filling in at bottom, or by 

 putting in bridges. This work is often very expensive 

 and, wherever possible in laying out a road, the expert 

 engineer will throw his line along the side and around 

 the end of steep hills, even though the distance be some- 

 what greater, for the increased travel is more than offset 

 by the increased hauling capacity. It is almost impossible 

 to avoid a considerable grade in constructing a road 

 over a hill. It often happens that a road may be thrown 

 around a hill instead of over it, without increasing the 

 distance to be traveled. This may be illustrated by 

 cutting a well-formed apple in halves. With a tape-line 

 find the exact center on the side and between the ends. 

 Then measure the distance over the piece of apple and 

 the distance around either end to the exact center of the 

 opposite side, and it will often be found about the same. 



It has been found that when a horse can pull a 1,000- 

 pound load on a level road he can draw only 900 pounds 

 up a 1 per cent grade, 800 pounds up a 2 per cent grade, 

 400 pounds up a 5 per cent grade, and only 250 pounds 

 up a 10 per cent grade. It might be interesting to deter- 

 mine the grade of some hills in the school district. A 

 spirit-level and a tape-line will be needed. 



A horse may pull only one-fourth as much on a 10 

 ^>er cent grade as might be pulled on a level road. How- 



