CHAPTER XXI 



NIGHT SIGNALLING 



Section 117 Signalling-lanterns 



Although the variety of lanterns available for night signalling is very great, the 

 actual use of such equipment in forest-protection communication has been extremely 

 limited. 'Signal-lanterns .are of two principal types, those which form code letters 

 t>y the display of two colours in the proper sequence, and those which form code letters 

 by flashes of one colour only, showing dots and dashes as with the heliograph. The 

 range of the first class is entirely too short to be of any use in forest protection. The 

 second class offers greater possibilities. 



Flash lanterns for signalling purposes are available, using as the source of light 

 acetylene gas, oil, gasolene, limelight, and both incandescent and electric arc lamps. 

 Two principal types are employed; those which burn continuously and operate with a 

 screen like a fixed-flash heliograph, and those which operate with a key and burn 

 intermittently only. The oil, gasolene, limelight, and arc lamps are of the first type. 

 The acetylene and incandescent lamps are of the second type. 



1 TYPES OF SIGNAL-LANTERNS 



'Signal-lanterns of various forms are employed principally for military and naval 

 communication purposes. The ordinary electric searchlight makes an excellent signal- 

 lantern and can be used either behind a screen for the sending of Morse signals, or 

 the beam can be used to send wigwag signals even between stations that are not them- 

 selves intervisible. It is not, however, a practical lamp for forest communication 

 because of the large amount of power required for its operation, not to mention its 

 great weight and lack of portability. 



Among readily portable signal-lanterns two principle types are available. These 

 are the acetylene lantern, and the electric signal-lantern using dry cells as a 

 source of power. Both have to a limited extent been employed in forest-protection 

 communication. 



(a) Acetylene Lamps. The acetylene signal -lantern is used extensively by the; 

 American Army Signal Corps, and the most read'ily procurable lanterns of this 

 type are those adopted by that Service. Two sizes, the field lantern and the station 

 lantern, are employed. For lookout use the station lantern, which is the larger, is 

 preferable as it is as readily portable as the requirements of this service demand 

 and has by far the longer range. 



This lantern is built in 4he form of a small searchlight with a 5-in., aplanatic 

 lens mirror and S-in. focus. It is mounted on a 'suitable tripod .and equipped with 

 a special gas-generator, a sighting-tube, and a small reading-lamp, the whole equip- 

 ment weighing about 20 pounds. The generator is hung to the legs of the^tripod 

 beneath the lantern and is charged with 1 pound of calcium carbide and 1 gallon of 

 water. This charge is sufficient for about 5 "hours' -signalling, and recharging 

 requires only a few minutes. 



The sighting-tube in the form of a small telescope is attached to one side of the 

 lantern. It is provided with cross-hairs and i-s used to direct the beam of light on 

 the distant station. Once the lantern is properly aligned, it requires no furtl. 

 adjustment, in which respect it is much superior to the heliograph. 



The supplementary reading-lamp is required with all forms of 'signal-Ian terns, 

 as the intermittent flashes of the signals do not afford light enough for reading or 

 recording messages. It is an acetylene lamp also, securing gas from the generator 

 that supplies the signal-lantern. 



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