_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|Intensity of light in|HP (actual) to | of armature. | standard candles. | drive. -------+---------------------+---------------------+-------------- Medium | 800 to 850 | 4,000 to 6,000 | 3-1/2 to 4 -------+---------------------+---------------------+-------------- The intensity of the unassisted light is given in standard candles. The standard here used is a stearine candle consuming 10 grammes per hour. _Regulation._--From the fact that a closed circuit rotating in a magnetic field experiences resistance to its motion which a broken circuit does not, motive power to any extent is only required when the circuit is closed. An interruption of the current is therefore equivalent to removing the load from the motor, which for mechanical reasons may be injurious to it and for electrical reasons to the dynamo machine. The sudden interruption of the circuit of the large machine produces an electric tension so dangerously high as to strain or destroy the insulation of the machine. When contact is again made after such interruption, the increase of speed resulting from the interruption causes a momentary current of great intensity, accompanied by sparks at the commutator. In order that the light may be quite steady the speed should be as uniform as possible. As too high an increase of speed may result in temporary extinction of the light, it ought never to be permitted. The motor should therefore be provided with a good and sensitive governor, that will keep the speed perfectly uniform however the steam and load may vary. A large and heavy fly-wheel is also very useful in keeping the speed nearly uniform during change of load.