6G MECHANICS. 



The following table shows the rise in a mile of road for 

 different ascents : 



For a rise of 1 foot in 10, tlie road ascends 528 feet per mile, 



do. 1 do. 13, do. 406 do. 



do. 1 do. 15, do. 352 do. 



do. 1 do. 20, do. 264 do. 



do. 1 do. 25, do. 211 do. 



do. 1 do. 30, do. 176 do. 



do. 1 do. 35, do. 151 do. 



do. 1 do. 40, do. 132 do. 



do. 1 do. 45, do. 117 do. 



do. 1 do. 50, do. 106 do. 



do. 1 do. 100, do. 53 do. 



do. 1 do. 125, do. 42 do. 



The same kind of reasoning applied to a common good 

 road will show that it will be profitable for the public to 

 travel about half that distance to avoid a hill of one 

 hundred and five feet. In this case the whole yearly 

 cost of the road, including interest on the land, and the 

 cost of repairs, would not usually be more than a tenth 

 part of the same cost for plank, or would not exceed thirty 

 dollars. 



On rail-roads, where the resistance is only about one- 

 fifth part of the resistance of plank roads, tlie dispropor- 

 tion between the draught on a level and up an ascent be- 

 comes many times greater. Thus, if a single engine move 

 three hundred and fifty tons on a level, then two engines 

 will be required for an ascent of only twenty feet per 

 mile, four engines for fifty feet per mile, and six engines 

 for eighty feet per mile. 



Such estimates as these merit the attention of the 

 farmer in laying out his own private farm roads. It may 

 be worthy of considerable effort to avoid a hill of ten or 

 twenty feet, which must be passed over a hundred times 

 yearly with loads of manure, grain, hay, and wood. The 

 greatly increased resistance of soft materials, also, is too 

 rarely taken into account. A few loads of gravel, well 

 applied, would often prevent ten times the labor in plow- 



