ON DRAUGHT. 



551 



f'ig.'6'6. 



the House of Commons, A carrier of Exeter was in favour of these wheels, and 



in support of his opinion, adopts them to this 

 day. But a few days ago we saw one of his 

 waggons with wheels, which, although only 

 about twelve inches wide, were six inches 

 smaller at the outside than at the inside. 

 Such a cone, if set rolling and left to itself, 

 would run round in a circle of little more 

 than twenty feet diameter. What must be 

 the grinding and the friction, then, when it 

 is constantly compelled to go on hi a straight 

 line ? yet enough has been written and said 

 upon this subject to convince, we should ima- 

 gine, the most prejudiced of the absurdity 

 of the system. 



We shall repeat the principal arguments which were made use of at the 

 time of the inquiry mentioned. 



Mr. Cummins took great pains, by constructing models, to show that conical 



wheels were not adapted for rolling in a 

 straight line, by making a small conical 

 wheel run over longitudinal bars, as in 

 fig. 33. It was seen that if the middle 

 part of the tire rolled upon the centre 

 bar without moving it, the bar A was 

 pushed backwards, while the bar C was 

 pushed forwards ; clearly showing if, in- 

 stead of sliding bars, the wheel had 

 moved upon a road, how much it must 

 have ground the road, and what a small 

 portion of the tire was truly rolling. 



That such must have been the case is 

 indeed, easily proved without a model. 

 We will take only three different parts of 

 the wheel and consider them as inde- 

 pendent hoops of different diameter ; if these hoops are compelled to go the 

 same number of revolutions, the large one will evidently gain upon the second, 

 while the third will be left far behind. Now, if, instead of being independent 

 of each other, they be fixed to the same axle, and compelled to revolve 

 together, the large one not being able to advance faster than the others, must 

 tear up the ground. The smaller one, on the contrary, being dragged forward 

 faster than it would naturally roll, must drag up the ground ; and this is what 

 must take place, and does, with any but a cylindrical wheel, and that to a very 

 considerable extent. 



Suppose, for instance, a conical wheel, of an average diameter of four feet 

 six inches ; that is to say, that the centre advances about fourteen feet to every 

 revolution of the wheel. If the inner tire be six inches larger in diameter 

 than the outer tire, the circumference of it will be about eighteen inches greater; 

 therefore, at each revolution of the wheel the inner tire would naturally advance 

 eighteen inches more than the outer tire : but they are compelled to go over 

 the same distance of ground. The one or the other, therefore, must have dis- 

 turbed the ground, or, what is nearer the truth, upon every fourteen feet of 

 road run, the former has passed over nine inches less ground than the development 

 of its circumference, the latter nine inches more the one pushing back the 

 ground, the other dragging it forward, or, which would be equivalent to the 



