252 Ohervations upon Wheel-Carriage Experimetits. 



proper ties of tl'.e cone do not appear to me to be in any manner 

 concerned in the cause of t!ie motion alluded to. 



The centre of the box is supposed to be in the centre of the 

 wheel, and to be fitted to the axle, whether it be a cone or a 

 cylinder ; the wheel is confined between the shoulder on one 

 side, and the nut on the other, on the axle in both cases, against 

 either of which the wheel will work with iiurea'^cd friction, ac- 

 cording to tlie directions of tiie forces applied. This tremulous 

 motion can at any time be produced njton a jjaved or hard and 

 uneven surface, by the wlicels not being paralkl, or by being 

 obliged to go forward, with the carriage, in directions not in the 

 respective plains of their circumferences, whether the axle be a 

 cone or a cylinder. 



In either of these cases there are lateral, and not conical mo- 

 tions imposed upon them, which uj)on ])avement become injurious 

 and particularly conspicuous — upon a smooth road less so, but 

 increase much the difficulty of drauglit upon a soft road, in pro- 

 portion to the depth to which the wheels may happen to sink. 

 The position of such axles as used in this experiment, and neces- 

 sarily tlie position of the xvheels, is ever governed by the eleva- 

 tion or depression of the shafts in a two-wheeled carriage, — had 

 their axles been cylindrical, and placed horizontally, these difri- 

 culties would not have existed. The wheels of the car, that 

 drew the greater load, were several inches higher than the other, 

 and the flexibility of its springs was very great, while those of 

 the other car were strong enough for the largest mail-coach. 

 The experiment would proliably have been less rough, had the 

 carriages been previously weighed, an indispensable requisite ujion 

 such an occasion, and the springs of both cars rendered inflexi- 

 ble during the operation, that was supposed to equalize them ; 

 but their equalization, as attempted, was (juite impossible to be 

 adequately accomplished, while they differed so materially in the 

 essential points, viz, fiexibilitv of springs, height of wheels, and 

 difference of weight, independent of any irregularities caused by 

 the use of men in front. — The superiority, that would have ap- 

 peared in one carriage by pliability of springs and height of 

 wheels, Vv'as countervailed by the embarrassing weight of its body, 

 and weights called equabzingv/eights, together weighing eighty- 

 eight pounds more than the yellow car with its embarrassments. 

 The equalization of ihe cars in the manner, made use of for this 

 experiment, is a case somewhat similar to the deceitful balance. 

 See Helsham's Lectures. 



I am indebted for a knowledge of the weights of these car- 

 riages to the kind accommodation given me at the weighing ma- 

 chine of the Farming Society of Ireland, a few days subsequent 

 to these experiments^ since which time, I understand the car- 

 riages 



