Since a resistance amounting to 33,000 pounds moved through one foot per minute is called one-horse power, it is evident that the horse power H of the engine is nothing more than the useful effect per minute referred to a larger unit of weight or resistance; that is to 33,000 pounds instead of one pound. Hence we shall have
| H = | U | .(26.) |
| 33000 |
Since the useful effect expressed in (24.) and (25.) is that due to a number of cubic feet of water, expressed by W, we shall obtain the effect due to one cubic foot of water, by dividing U by W. If, therefore, U′ be the effect produced by the effective evaporation of a cubic foot of water, we shall have [Pg517]
| U′ = | U | .(27.) |
| W |
If the quantity of fuel consumed per minute be expressed by F, the effect produced by the unit of fuel, called the DUTY of the engine, will, for like reason, be
| D = | U | .(28.) |
| F |
If the fuel be expressed in hundredweights of coal, then D will express the number of pounds' weight raised one foot by a hundredweight of coal.
By solving (24.) and (25.) for W, we obtain
| W = | U{R(1 + m) + b + r} | ,(29.) |
| Re′ |
| W = | 1 | {U(1 + m) + VA(b + r)}.(30.) |
| e′ |