ON RAIL-ltOADS.

247

the phenomena of their action, and this again,perhaps, cannot be ascertained without subject-ing them to the test of experiment. Observa-tion and experience may guide us in forming ajudgment of the performance of any engine,but it is only by subjecting them to experimentsin all their various modes of action, that theirgeneral law of action is developed.

To accomplish this, 1 commenced a series ofexperiments on the Killingworth Rail-road,with the engines there used; and, by applyingdifferent engines with the same load, and alsothe same engine with different loads, I wasenabled to ascertain, with nearly perfect accu-racy, the relative performances both withrespect to weight, and also to velocity.

With the expectation of reducing the friction,and also to obtain the performance at differentrates of speed, I affixed larger travelling-wheelsfo the engine, and, by experimenting uponthe same engine, with different-sized wheels,I was not only enabled to prove the relativeperformances of wheels of different diameters,but also to ascertain the actual amount offriction inherent in the engine itself.

The following Tables will shew the result ofthese experiments.