He invented the rheostat and improved the resistance balance, invented by S.
- A, antenna; P S, jigger or oscillation transformer; C, condenser; 0, Fleming oscillation valve; B, working battery; T, telephone; R, rheostat; E, earth-plate.
Suppose the key to be depressed, then a current flows through one winding of the differential relay to line and through the other winding and rheostat to earth.
Now if the values of the rheostat and condenser are adjusted so as to make the rise and fall of the outgoing current through both windings of the relay exactly equal, then no effect is produced on the armature of the relay, as the two currents neutralize each other's magnetizing effect.
The framework carrying the clamps is arranged so that a number of determinations may be made at one time, the wires from the clamps running from a rheostat, so arranged that currents of any strength may be used simultaneously.