and Advantages of Wheels for Caniages, &c. 97 



diately at the carriage ; and the convenience of this draft as con- 

 nected with the insertion of the line of traction, which continued 

 ought to pass through the axis of the wheels, introduces another 

 limit to their size. 



Springs were in all likelihood apphed at first to carriages, with no 

 other view than to accommodate travellers. They have since been 

 found to answer several important ends. 



They convert all percussion into mere increase of pressure- 

 that is, the collision of two hard bodies is changed by the interpo- 

 sition of one that is elastic, into a mere accession of weight. 

 Thus the carriage is preserved from injury, and the materials of 

 the road are not broken : and, in surmounting obstacles, instead 

 of the whole carriage with its load being lifted over, the springs 

 allow the wheels to rise, while the weights suspended upon 

 them are scarcely moved from their horizontal level. So that, if 

 the whole of the weight could be supported on the springs, and 

 all the other parts supposed to be devoid of inertia, while the 

 springs themselves were very long, and extremely flexible, this 

 consequence would clearly follow, however much it may wear the 

 appearance of a paradox ; that such a carriage may be drawn over a 

 road abounding in small obstacles without agitation, and without 

 any material addition being made to the moving power or draft. 

 It seems, therefore, probable that, under certain modifications of 

 form and material, springs may be applied with advantage to the 

 very heaviest waggons ; and consequently, if any fiscal regulations 

 exist either in regard to the public revenue or to local taxation, 

 tending to discourage the use of springs, they should forthwith be 

 removed. 



Although the smoothness of roads and the application of springs 

 are beneficial to all carriages and to all rates of travelling, yet 

 they arc eminently so in cases of swift conveyance, since obstacles 

 when springs are not interposed, require an additional force to 

 urmount them beyond the regular draft, equal to the weight of 

 the load multiplied by the sine of the angle intercepted on the 

 periphery of the wheel between the points in contact with th 

 ground and with the obstacle, and therefore proportionate to the 



Vol. XVIII. H 



