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.
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.
If these conditions are not fulfilled sufficiently, the ammeter will not give the same indications for the same current if that current has been reached (a) by increasing from a smaller current, or (b) by decreasing from a larger current.