108 MECHANI(5S. 



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

 quarter tons. 



On the best broken-stone road, fifty to sixty-seven 

 times as much, or three to four tons. 



On a common plank-road, clean, fifty times as much, 

 or three tons. 



On a common plank -road, covered thinly with sand 

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

 two tons. 



On the smoothest oak plank-road, seventy to one 

 hundred 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 resist- 

 ance about one thhd. 



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

 could draw only about two thirds as much when it was 

 moist or dusty as when dry and smooth ; and when 

 muddy, not one half as much. When 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 which is 

 supported by the horse, usually requires only about 

 two thirds the force of hori2ontal 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 



