CH. Ill CONED WHEEL 43 



of action takes place in a less degree with a less 

 amount. 



We have so far assumed that the road is flat 

 crosswise ; the conditions will be changed if the 

 cross section is different. 



To take an exaggerated case, such as might occur 

 in a special piece of machinery : the treads of the 

 wheels, and the axles, must be parallel to the sur- 

 faces on which they run in order to 

 determine a straight direction, as in 

 Fig. 24 ; and in the case of a road, 

 the cross section of which is curved, 

 a straight, not a coned, wheel, with 

 the axle bent down so as to bring 

 the tire to bear flat on the road, 

 would be correct. This probably 

 gave rise to the early practice of building vehicles 

 in this manner, but it is obvious that to be correct, 

 the cross section of the road must be the same in 

 all places, which is not likely to be the case. 



All roads are somewhat lower at the sides than 

 at the middle, and when a carriage leaves the cen- 

 tre, it inclines toward the gutter, so as to throw the 

 weight more on the down side wheel and to take it 

 off the higher wheel. The danger always is, there- 

 fore, of bending the wheel from its inside outward, 

 but not in the other direction ; this is resisted by 

 the shape of a dished wheel, as the hub cannot 

 possibly be pushed through from the back with- 

 out compressing and shortening the spokes ; an 



