244

MOTIVE POWER EMPLOYED

bo loaded; and this would be sufficient todrag about 70 tons upon a level road. Theengine-wheels, however, as stated in the expe-riment, slipped a little, and though the pro-gressive motion was notwithstanding kept up,yet such a slipping of the wheels w ould havea very injurious effect, not only upon thewheels, but also to the rails. The load shouldnot, therefore, be so great as to produce suchan effect.

Prom several years’ observation of theirperformance upon the Killingworth Rail-road,I am inclined to think the above rather toohigh, without incurring the risk of slipping.There they travel sometimes with 9 and some-times with 12 carriages, amounting to 36 and48 tons respectively. The greatest ascent,upon any part of the Rail-road w ith the load,is 1 in 330; and in returning, with the emptycarriages, 1 in 80. The wheels, in very bad

weather, slip sometimes with 12 carriages ;but, the engines, in the worst weather, arenever prevented travelling with 9 carriages.

Talcing the latter as the datum, we have 8764 lbs. the

1

weight of each carriage X 9x 330 = 61 lbs., the gravity_ 1

of the carriages. And 16800 + 3360 x 330 = 239 lbs., thegravity of the engine and convoy. Then 9 x 40 — 360lbs.,the friction of the carriages, and 17 lbs. the friction of the