A Rheostat is a device for controlling the amount of electricity in a conductor—by the insertion of coils of wire in a box—which may be successively switched in or out of the main circuit by means of a lever and button-switch. The best place to install a rheostat is on a wall or post, as the resistance transforms a portion of the electric energy into heat, which heat must be dispersed into the atmosphere.
A transformer is an induction coil employed usually for lowering electric pressure, but it may also be used for raising the same, in which case it is sometimes called a booster. A compensator is a transformer which works automatically.
Fig. 231.
Fig. 232.
Ammeters record the quantity of current flowing through the circuit, in amperes. Voltmeters record the pressure or strength of the current in volts.
An Ampere is an electric current which would pass through a circuit whose resistance is one ohm under an electro-motive force of one volt. A Volt is an electro-motive force of sufficient strength to cause a current of one ampere to flow against a resistance of one ohm.
The ampere is the unit for calculations relating to the quantity or volume of a current; the volt is the unit for calculating the pressure or strength of the current.