The brushes collect the electric currents as they are induced, which is nearly constant and continuous.
The collecting brushes are combs of copper wire placed tangentially to the cylindrical commutator, and press lightly upon it with an elastic pressure.
Power and Light produced.—An increase of the armature speed produces a corresponding increase in the current produced, but not in the same proportion. The current increases more rapidly than the speed, and could be made to reach any intensity but for considerations explained below. With increase of current there is also increase of heat.
The speed for continuous work must not be taken too high, because the heat developed at high velocities might destroy the insulation of the coils of the electro-magnet. The speed given for this machine produces no such injurious heating effect.
The strength of the current is also influenced by the resistance of the electric lamp and its leading wires. With an electric lamp in a circuit of proper resistance the armature should revolve at the rate given in the following Table. The heating will then reach its maximum, which is very moderate, in about three hours after which there will be no further change.
Table.
| Size. | Number of revolutions of armature. | Intensity of light in standard candles. | HP (actual) to drive. |
| Medium | 800 to 850 | 4,000 to 6,000 | 3½ to 4 |