18S

FRICTION OK CARRIAGE*

also another variation in the result, owing tothe different kinds of bearings employed.Comparing the resistance of No. 8 with No. 7,there appears a difference of four pounds,which is equal to one pound in each carriage,between bearings of cast-iron and of brass, theiron bearings are broader than those of thebrass, and this will, perhaps, account for thedifference ; otherwise the brass w ould mostlikely have been found to present the leastfriction ; but it at the same time proves thenecessity of making the bearings of a certainsize, compared with the pressure upon them,and shows that the brass is considerably belowthat size; inasmuch, as we find that the in-creased breadth of the cast-iron more thancompensates for its inferiority to brass, indiminishing the friction.

We had also an opportunity of subjecting tothe test of experiment, another kind of bear-ing, which, for a long period after the intro-duction of Rail-ways, was universally used,and I believe is still used in many places.—This is a malleable iron bearing, formed bythe hammer of the blacksmith, one inch and aquarter broad ; this was the bearing used inNo. 11, which, on being compared with Nos.7 and 8, a difference will be found amountingto 19 lbs. between that kind of bearing and the