Balance, Ampere

A cla of electrical measuring instruments due to Sir William Thomson may be grouped under this head. The instrument is a true balance or scales such as used for weighing. It is supported by a torsional wire support in place of knife edges. At each end it carries a circle of wire through which the current to be tested is pa ed. The torsional wire support enables the current to be carried to these wire rings. Above and below each of these rings are two similar rings, also connected so as to receive the current. They are so connected that the current shall go through them in opposite senses. When a current pa es, therefore, one of these rings repels and one attracts the balanced ring. The extent of this action measures the intensity of the current. A sliding weight moving along a graduated scale on the balance is used to bring the balance beam into equilibrium when the current is pa ing. The degree of displacement of this weight gives the strength of the current in amperes. These balances are made for different currents. Thus there is a cent i-ampere balance, deka-ampere balance and others, as well as an ampere balance.