In its simplest form an electromagnetic ammeter consists of a circular coil of wire in which is pivoted eccentrically an index needle carrying at its lower end a small mass of iron.
Such an instrument is called a soft-iron gravity ammeter.
Such a test is made by determining with an accurate ammeter or watt-meter the current or power supplied to a circuit for a period measured by a good clock and comparing with this the actual reading of the meter 2 See Journ.
The capacity of the condenser is then altered until the maximum current, as indicated by a hot wire ammeter, is produced in the circuit.
There is therefore a certain ratio in which any current passing through the ammeter is divided between the shunt and the working wire.