193
On examining the result of the foregoingexperiments, we find the friction is not pre- rcisely proportionate to the weight, but nearlyso. The friction of the rubbing upon the axle,and the resistance of the wheels upon the rail,does not appear to follow the same law. Itwould have been highly desirable if they couldhave been subjected separately to the test ofexperiment, that we might be able to deducefrom the known amount of friction of the one,the friction of the other ; but, in the absenceof such experiments, we must content our-selves with as near an approximation as theextent of our information reaches. Assumingthe friction to be as the weight, and takingNo. I. as a standard, we should have for theother, when the whole weight of carriage andwheels is taken into account, 53 and 64lbs.respectively, whereas, experiment gives 48 and58lbs. which shows that the friction does notincrease in so great a ratio as the weight.This, no doubt, arises from a part of the wholeweight being subjected to the action of rollingonly, (viz. the weight of the wheels and axles,)the resistance from which cannot amount to somuch as a like weight, subjected to the actionof attrition upon the axle, and also of the roll-ing of the wheel upon the rail, as takes placewith the body of the carriage resting upon theaxles. n