ON RAIL-ROADS.

259

Hy further enlarging the diameter of thewheels, however, a corresponding increase ofeffect will not take place, because the reductionof friction will then only be in the ratio of the dia-meter of the wheels upon the diminished frictionof the engine, or to one-fourth of3841bs., and thistoo will only take place if the construction ofthe engine be not altered. If the diameter ofthe axles be increased, so as to compensatefor the additional strain by large wheels, theextent of rubbing surface will be thereby alsoincreased, and the diminution lessened accord-ingly ; but, as this increase would form onlya small part of the whole friction, the use oflarge wheels to effect an increase of velocity inthe engine will always be of great advantage.

My next object was to ascertain the con-sumption of fuel, both as regards its absolutequantity, and also the comparative quantitywith different, loads.

An inspection of the result of the experimentsgiven in the Tables will shew this ; but, as itwill be found that the quantity varies much, itmay be necessary to enter a little more intodetail respecting the cause of such variation ;and this explanation will also be the meansof shewing a very important discovery in theconstruction of engines for diminishing thequantity of fuel.