438 



ON DRAUGHT. 



wheel, it was monstrous. Yet tliis is the 

 form of wheel upon which the contradic- 

 tory opinions referred to in the first page 

 of this treatise, were given before a com- 

 mittee of the House of Commons. A car- 

 rier of Exeter advocated 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 

 than at the inside. Such a cone, if set a 

 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 a straight line ? yet enough has been written 

 and said upon this subject to convince, we sliould imagine, the most preju- 

 diced of the absurdity of the system. 



We sliall reoeat the principal arguments which were made use of at the 

 time of the mquiry mentioned. 



Mr. Gumming 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 longi- 

 tudinal 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, 

 instead of sliding bars, the wlieel had 

 moved upon a road, how much it 

 must have ground the road, and what 

 a small portion of the tire was truly 

 rolMvg. 



That such must have been the case 

 is, indeed, easily proved without a 

 model. We will take only three dif- 

 ferent parts of the wheel, and consider them as independent hoops of differ- 

 ent diameter; if these hoops are compelled to go the same number of revo- 

 lutions, the larger 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 are 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, witii any but a cylindrical wheel, and that 

 to a very considerable extent. 



Suppose, for instance, a conical wheel, of an average diameter of five 

 feet; that is to say, that the centre advances about fifteen 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 oue or the other 



