If it is desirable to use the lamp as a hand lantern the flame can be turned on full by turning the button in a vertical position; this locks the key open. In the new model depress the key and lock it with the latch above the key.
One charge of calcium carbide will supply gas to burn about one hour with the light turned on full, or for approximately three hours' signaling.
Fig. 10.
If signaling is to be suspended for some hours, empty the water out of the generator and close valve R.
The glass front can be replaced by taking out the wire spring. The glass cuts should be mounted in a horizontal position and, to prevent breaking, should be protected from rain when the lamp is hot. If a glass should be broken and an extra one is not available to replace it, signaling can be continued by turning the flame on full and using the heliograph shutter, a cap or piece of board in front of the lantern to obscure and reveal the flash. Without the protection of the cover the flame is easily blown out when turned low, but will not be extinguished even in a strong wind if the gas is turned full on.
Old model lamps are serially numbered from 1 to 200, inclusive; the new model lamps are serially numbered from 201 upward.
Powers and limitations of the acetylene signal lantern.—As conditions are usually more uniform at night than in the daytime, the signal lantern is probably the most reliable of all visual signaling outfits. The advantages of this form of apparatus are its portability, speed of operation, and comparatively great range. The principal disadvantages are due to the interference caused by rain, fog, and moonlight. The speed attainable with the lantern is about the same as that attainable with the heliograph.