Page:Inland Transit - Cundy - 1834.djvu/43

time, if the road and the faces of the wheels were perfectly smooth, and no resistance of the air. This is a consequence of one of the first and most simple properties of matter,—inertia; that property in virtue of which a body would remain for ever at rest, if not put into a state of motion by the action of some external force. But the formation of a perfectly smooth road, and of perfectly smooth wheels to move on that road, is impracticable in this country. The surface of the road and the surface of the wheels, whatever is their materials, or with whatever care they may be constructed, will be covered with asperities; which will obstruct the motion of the carriage in proportion to their number and magnitude, and in proportion to the weight with which the carriage presses upon them. The more these asperities are removed, therefore, the less will be the force of traction necessary to continue the motion of a carriage loaded with a given weight. Experiments made on an extensive scale by Coulomb, Ximenes, and other philosophers, have established satisfactorily, that, when the quality of the road and of the wheels are the same, the resistance of the motion of the carriage, arising from the roughness of the road, will always be in proportion to the weight of the carriage. A double weight will offer double resistance, a triple weight a triple resistance, and so on. The same experiments establish another consequence, materially affecting all questions respecting the work performed on roads. This result is, that the resistance to the motion of a carriage is altogether independent of the velocity of that motion; and that, whatever be the speed at which the carriage moves, the resistance will suffer no change. Indeed, any slight change