272 MOTIVE POWER EMPLOYED

645 lbs. the gravity of the whole train. And 43 X 0 ~ 215 lbs.

the friction of the carriages; then 645 + 215+ ( = *58 —

1018 lbs., the resistance, which, in the experiment, was movedthrough 1164 feet; whence 860 x 1164= 1001040, the effectproduced.

Therefore

53053280 power,^1001040 effect.

Whence we have the effective power equalto 33.3 per cent, of the pressure of the steamupon the piston, when the velocity of thepiston is 165 feet in a minute.

The above will shew how vague an idea wehave of the performance of a high-pressureengine, by expressing it in terms of horses’power, calculated by applying to the area ofthe piston the pressure of the steam in theboiler.

The first of these experiments gives 70 percent, effective power, and the other 33.3 percent., while in each the elasticity of the steamin the boiler remained the same. The truemeasure is the quantity, or rather the weight,of steam expended. The weight of steam is,of course, as its density, indicated by the weighton the valve confining it; and the latter, in thetwo experiments, will be proportionate to therespective intensities of the load ; the effect ofthe first is 18101bs. moved over 1164 feet in