| AA. | Bell-bobbin coils. |
| B. | Iron base. |
| C. | Wire from battery terminal joined with one end of coil wire. |
| D. | Other end of coil wire. |
| E. | Wire from other battery terminal. |
Fig. 9.—Showing connections for passing current round bell-bobbin coils.
Experiment 3.—Repeat the previous [experiment] whilst using pieces of carbon, round which the free wire ends (D and E, [Fig. 9]) are twisted, to bring into contact with one another ([Fig. 10]). The spark obtained is very bright, and may possibly by careful handling be maintained for a moment or two; if the current is more powerful, the spark does keep constant, even though the carbons be drawn apart considerably, and thus forms in principle such an arc lamp as floods the streets of towns with their dazzling rays. The pieces of carbon may frequently be picked up beneath arc light standards, after the electrician has gone on his rounds “trimming” the lamps.
Fig. 10.—The principle of the arc lamp.
Experiment 4.—Again repeat the [No. 2] experiment, but insert a rough file in the circuit and drag the free end of a wire from the battery up and down its surface ([Fig. 11]). Sparks in plenty, but apparently frail and resembling those thrown off by squib fireworks, are produced in this manner.
Fig. 11.—More spark production.
