Influence of Grade on Draft. 433 



pected to carry the load over which it was able to bring 

 over a level dirt road to it. 



These results have been computed from the standpoint 

 of an 800-pound horse, but since the ability of a team to 

 work is in a general way proportional to its weight the 

 same results would have obtained had we taken the 1 2 600- 

 pound horse with a proportional load. 



533. Good Roads Make High Grades More Objectionable. 

 When the good macadam road-bed is substituted for the 

 common dirt road then the same draft, 140 pounds, which 

 draws a ton on the dirt road will draw 



140 



=~Z = 2J times as much or 4, 666f Ibs. = 2J tons. 



on the level macadam road. Since it requires but 60 Ibs. 

 to move a ton on a macadam road the team may come to 

 the hill with a load of 



^ 2| tons = 6,933 * Iba. 



The effective power of the team will be 

 400 - 160 = 240 Ibs. 



Up how steep a grade will 240 Ibs. carry the team and 

 2} tons? Solving this as we did the other we get 



240 X 100 == 6,933 X W. D. 

 whence W. D. = ? = 3.46 



or a little less than a 3.5 per cent, grade. That is to say, 

 when a dirt road is improved so as to reduce the draft from 

 140 Ibs. per ton to 60 Ibs. per ton then, in order to utilize 

 this improved road with equal effectiveness under the con- 

 ditions assumed, the 6.2 percent, grade should be reduced 

 to 4 per cent. ; and the highest grade could not exceed 

 9.23 per cent. 



