ON RML-KOADS.

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of nibbing surface, when the friction is aminimum ; for, if the bearing be extremelynarrow, the surface in contact with it will becut; anti if, on the contrary, it be very broad,an unnecessary extent is exposed. The pre-cise proportion can only be ascertained byexperiment, and it would certainly be confer-ring a great boon to science, were that deter-mined by a set of experiments upon a largescale. Whatever be the ratio of the size ofthe bearing to the weight of the body, thefriction, upon similar bearings, will alwaysbear a determinate proportion to the entireweight of the body.

There are other species of obstructionpresented to the motion of carriages, besidesthose already enumerated, such as the actionof the wind, &c.; but as their effects, inretarding the motion, are comparatively tri-vial, at moderate velocities, or at that rate ofspeed at which carriages usually travel, womay, in general, omit noticing their effect.

It has been a matter of just regret, that sofew experiments have been made to ascertainthe degree of resistance arising from frictionto carriages moved along Rail-roads; on asubject of such importance it is astonishingthat, until lately, so little interest shouldhave been excited, comprehending, as it were.