86 MECHANICS. 



On a common broken-stone road, twenty-five to tliirty- 

 six times as much, or one and a half to two and a quarter 

 tons. 



On the best broken-stone road, iifty to sixty-seven times 

 as much, or three to four tons. 



On a common ^^lank-road, clean, fifty times as much, or 

 three tons. 



On a common plank-road, covered tliinly with sand or 

 earth, thirty to thirty-five times as much, or about two 

 tons. 



On the smoothest oak plank-road, seventy to one hund- 

 red times as much, or four and a half to six tons. 



On a highly-finished stone track-way, one hundred and 

 seventy times as much, or ten and a half tons. 



On the best rail-road, two hundred and eighty times as 

 much, or seventeen and a half tons. 



The firmness of surface given to a broken-stone road by 

 a paved foundation was found to lessen the resistance 

 about one-third. 



On a broken-stone road it was found that a horse could 

 draw only about two-thirds as much when it Mas moist 

 or dusty as when it was dry and smooth; and when 

 muddy, not one-half as much. "VYhen the mud was thick, 

 only about one quarter as much. 



The character of the vehicle has an influence on the 

 draught. Thus, a cart, a part of the load of wliich is sup- 

 ported by the horse, usually requires only about two-thirds 

 the force of horizontal draught needed for wagons and 

 carriages. On rough roads the resistance is slightly 

 diminished by springs. 



On soft roads, as earth, sand, or gravel, the number of 

 pounds draught is but little affected by the speed; that is, 

 the resistance is no greater in driving on a trot than on a 

 walk ; but on hard roads it becomes greater as the velocity 

 increases. Thus a carriage on a dry pavement requires 

 one-half greater force when the horses are on a trot than 



