STANDARD ELECTRIC INSTRUMENTS.
STANDARD DIRECT READING ELECTRIC BALANCES.
1. These instruments are founded on the mutual forces, discovered by A npere, between movable and fixed portions of an elec.ric circuit. The shape _^»©sen for the mutually-influencing portions is circular, and each such part will be called for brevity, an Ampere ring ; or sometimes simply a ring, whether it consists of only one turn or of any number of turns of the conductor ; or an arc when it consists of less than a whole turn.
2. In each of the balance instruments, except the kilo-ampere balance, each movable ring is actuated by two fixed rings—all three approximately horizontal. There cire two such groups of three rings—two movable rings attached to the two ends of a horizontal balance anii pulk d, one if them up and the other down, by a pair of fixed rin in its neighbourhood. The current is in opposite direi 'ons through ihe two movrble rings to practical'}- annul disturbance due to horizontal components of terrestrial or local magnetic forces. In the kilo-ampere balance the whole o^rtnt passes through a single