452 



ON DRAUGHT. 



railway ; '^o.nd^ Jig. 41 represents an end 

 view of the rail with a pair of wheels. The 

 ground is afterwards filled up nearly to 

 the level of the bars, leaving only about 

 one inch of their upper edge exposed : 

 upon this the wheels run. The wheels are 

 generally of cast iron, about three feet in 

 diameter, and slightly conical, v/ith an 

 edge or flange inside, to guide them in 

 the centre of the rails. This brief de- 

 scription is sufficient to give a general 

 idea of the construction of railways, which is all that is necessary for 

 our present purpose. It will be easily conceived that hard, cast-iron 



Mk 



Fig.U. 



A 



wheels, running upon smooth edges of iron in this manner, can meet with 

 but little resistance except those arising from friction at the axle. 

 Accordingly, we find, upon a well constructed railway, in good order, tliat 

 the resistance does not exceed, in any sensible degree, that which must 

 arise from this cause. It has been found that a force of traction of lib. 

 will put in motion a weight of 180, 200, and even, in some cases, 2501b. : 

 so that a horse, exerting an effort of only 1251b., would drag on a level 

 10 tons. This is about ten times the average effect of his work upon a good 

 common road, and, as it arises entirely from the hardness and smoothness 

 of the road, we cannot conclude our observations by a more striking and 

 unanswerable argument than this, in proof of the immense advantages and 

 saving of expense which would result from greater attention to the state 

 of the roads. 



