260 MOTIVE POWER EMPLOYED

The experiments were made with two en-gines, which I have termed No. I. and No. II.,the first forming- the experiments of Table VI.and the latter of Table VII. The construc-tion of both engines were precisely the same,except in the size of the tube which passesthrough the boiler; no part of the boileritself, as will be seen on examination of thedrawing, is exposed to the direct action of theignited fuel ; a tube is put through the boiler,within which, upon grate bars, the fuel isplaced, and, in this manner, the heat is commu-nicated to the water in the boiler. The extentof surface of the water exposed to the directaction of the fire, will then be equal to thesemi-periphery of this tube. In the No. I.engine this tube was 20 inches diameter; and,in the No. II. engine, 22 inches diameter; and,except a corresponding difference in the sizeof the chimney, the two engines were, in everyother respect, the same.

Comparing Experiment XXIX with XXXII.where the same load was taken, we find thequantity of fuel consumed by the former, intravelling 63280 yards, to be 2534lbs., and, inthe latter, for travelling on the same ground,45200 yards, equal to 1487 lbs. Then, as63280 : 45200 : : 1487 : 2101 lbs. Therefore,the relative consumption of fuel by the two