THE RESISTANCE OF EOADS. 65 



in this particular, but the following may be considered as 

 about a fair average. In drawing a ton weight (including 

 wagon) on freely running wheels, on a perfect level, the 

 strength exerted will be found about equal to the follow- 

 ing : 



On a hard, smooth plank road 40 pounds. 



On a good Macadam road 60 " 



On a common ^ood hard road 100 " 



On a soft road about 200 " 



!N'ow let us compare this resistance to the resistance of 

 drawing up hill. First, for the plank road forty pounds 

 is one-fiftieth of a ton ; therefore a rise of one foot in fifty 

 of lengtl^ will increase the draught equal to the resistance 

 of the road. Hence the road might be increased fifty feet 

 in length to avoid an ascent of one foot ; or, at the same 

 rate, it might be increased a mile in length to avoid an 

 ascent of one hundred and five feet. But in this estimate 

 the increase in cost of making the longer road is not taken 

 into account. If making and keeping in repair be equal 

 to three hundred dollars yearly per mile, and one hundred 

 teams pass over it daily, at a cost for 'traveling of four 

 cents each per mile, being four dollars daily, or twelve 

 hundred dollars per annum, then the cost of making and 

 repair would be one quarter of the expense of traveling 

 over it. Therefore the mile should be diminished one 

 quarter in length to make these two sources of expense 

 counterbalance each other. Hence a road with this 

 amount of travel should, with a reference to public 

 accommodation, be made three-fourths of a mile longer 

 to avoid a hill of one hundred and five feet. This 

 estimate applies to loaded teams only. For light car- 

 riages the advantages of the level road would not be so 

 great. One-half to five-eighths of a mile would, there- 

 fore, be a fair estimate for all kinds of traveling taken 

 together. 



