396 On the Wheels and Springs of Carriages. 



of the cosine of the angle to radius. When obstacles fre- 

 quently occur, it had better perhaps receive a snlall inclination 

 upwards, for the purpose of acting with most advantage when 

 those are to be overcome. But it is probable that different 

 animals exert their strengths most advantageously in different 

 directions, and therefore practice alone can determine what 

 precise inclination of this line is best adapted to horses, and 

 what to oxen. These considerations are, however, only ap- 

 plicable to cattle drawing immediately at the carriage ; and the 

 convenience of this draft, as connected 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 applied 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 

 interposition 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 ob- 

 stacles, 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 horizon- 

 tal level. So that, if the whole of the weight could be sup- 

 ported 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, there- 

 fore, 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 taxa- 

 tion, 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 tra- 

 velling, yet they are eminently so in cases of swift conveyance, 

 since obstacles when springs are not interposed, require an 

 additional force to surmount 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 the ground and with the obstacle, and 

 therefore proportionate to the square of its height; and a still 



further 



