ON RAIL-ROADS.

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wheels of the carriages. The experimentswere performed with the strictest regard toaccuracy ; the coals were measured by a stan-dard coal-tub, strike measure; and, to be certainwith regard to the weight, several tubs werealso weighed, and the difference of weight,which was scarcely worth noticing, averaged.The water was also carefully measured.

In the first four experiments, the time wasmarked when the engine began to move fromthe end of the plane, so that the force required,and also the delay taken up in putting thecarriages into motion, was included. No attemptwas made to augment the speed of the engineto the greatest that could be performed ; myobject being to ascertain the relative perform-ances with different wheels and different loads.

I therefore endeavoured to keep up a speed asequable as possible, and, in doing so, I hadfrequently to regulate and check the velocityto obtain the same number of strokes perminute in each experiment.

In the fifth experiment or XXXIII, the enginewas allowed to traverse a given space, to putthe train of carriages into their proper velocity,before the time was noticed; the time was thenmarked until the velocity was again checked atthe farther end of the stage. This will explainthe difference between the two distances men-tioned in that experiment; the one was, the