242

MOTIVE POWER EMPLOYED

It will be evident, that the total amount ofadhesion is that force which would be requiredto cause the engine to slide along by itswheels upon the rail, if the wheels wereprevented from turning round; or that amountof force compared with its weight, which thefriction of other rubbing surfaces bear to theirweight. Knowing, then, the friction of ironsliding on iron, and the w eight of the engine,we could deduce the amount of adhesion ofan engine, compared with its weight; or, byfastening the engine-wheels, and employinga force to drag the engine, loaded with dif-ferent weights along the Rail-road, we could,by this mode, ascertain the amount of adhesionproportionate to the weight; either of these,though very correct modes of ascertaining thetotal amount of adhesion, compared with theweight, would not, perhaps, be so accuratea standard for practical application. The forceof the steam, at different periods of the stroke,being very irregular upon each wheel, mightoccasion the result, in practice, to vary fromthat deduced by the foregoing methods.

EXPERIMENT XXVII.

Loco-motive engine, weighing tons, andcontaining 1 ton of water, = 7 \ tons, dragged12 loaded carriages, each weighing 9408lbs.,