196

FRICTION OF CARRIAGES

exceeds the other, by so much is the quantityof rubbing surface diminished, and conse-quently the friction arising from that cause.

Column 7th expresses the proportion whichthe friction bears to the weight, compared withthe extent of rubbing surface upon the axles.Tlius, in No. 1, the friction is equal to the twohundred and nineteenth part of the carriage, andthis friction is caused by the action of thewheels rolling upon the rails, and the weightrubbing upon the axles; but the proportionwhich the action of the former bears to thelatter, is as 12.36 :1; we diminish then in thatproportion the friction; or at least that whicharises from the attrition upon the axle, andwhich, upon an edge rail-way, constitutes agreater part of the resistance ; and, by usingdifferent-sized wheels, we diminish the resist-ance from that cause, in direct proportion tothe difference between the diameter of thewheels and that of the axle.

Column 7 will then express the frictioncompared with the extent of rubbing surface.To find the friction of carriages placed uponany size of wheels, we have only to mul-tiply this sum by the diameter of the wheelsand divide by the diameter of the axle, and thedividend will give the friction or resistance ofthe carriage upon an edge rail-road.