1 pound raised 1 foot = 1 foot pound
550 foot pounds per second = 1 horse-power
778 foot pounds (1.4 H.-P.) = 1 B. T. U. (British thermal unit) = heat required to raise 1 pound of water 1° Fahrenheit
1 volt × 1 ampere = 1 watt
746 watts = 1 horse-power
In order to hold back 112 volts of electric pressure so that not more than eight amperes of electricity should pass, the iron wire must have offered about 14 ohms of resistance.
The behaviour of the ammeter needle showed that the wire offered very much less resistance when cold than when hot. Indeed eight feet of No. 24 iron wire offers about one and one third ohms resistance when cold, hence heat had increased its resistance to the passage of the electric current tenfold.
This piece of iron wire offered resistance to the flow of the electric current. It offered resistance to the motion of the dynamo. This offered resistance to the steam-engine which drives the dynamo. This caused the governor of the engine to open and pass more steam from the boiler. This reduced the pressure at the steam gauge. This caused the fireman to shovel more coal into the furnace. The heat of the burning coal melts the wire, but it does it only after several changes. First, it is converted into mechanical energy in the steam-engine with great loss—about nine tenths being lost. Second, it is converted into electrical energy by the dynamo, with some loss, and, third, it is conducted to the iron wire and converted back to heat with still further loss. It is evident that the most economical way to heat the wire would be to take it to the furnace. Yet all electric cooking is done by sending electric current through wires embedded in the walls of the cooking utensils, and it is the most wasteful method of using the energy stored in coal that has yet been devised.
