184 



METHODS OF COMMUNICATION FOR FOREST PROTECTION 



complete and may be mounted en a heliograph tripod. It can be easily read without 

 a telescope at 11 miles. The source of power in electric lamps such .as this is the 

 dry cell. In order to reduce battery consumption, all signal-lamps of this character 

 operate with a key or switch, by means of which the circuit is made and broken in 

 such a way as to form the letters of the Morse code. In the Stevens-Lyon lamp 

 this key is placed on the top of the lamp and is shaped like the ordinary Morse 

 key used in telegraphy. A sighting-tube and a small oil reading-lamp are also 

 provided and serve the purpose already described. This is a very compact, easily 

 portable and easily operated lamp, and within the limits of its range might often be 

 preferred to the acetylene lamps. 



For use with it the inert type of dry cell is made up with the excitant in the 

 form of a dry powder instead of the paste used in the ordinary dry cell. Cells of 

 this type are made ready for use by adding water through a tube placed in the cover 

 for the purpose. They have the great advantage of not deteriorating even when 

 kept stored for long periods. Such cells, however, are not read'ily procurable and 

 as a rule can be obtained on special order only. 



Fig. 107 Fischer high-power electric signalling lamp 



(c) Fischer High-power Lamp. The most promising signal-lamp thus far pro- 

 duced is the Fischer triangulation lamp used by the United States Coast and 

 Geodetic Survey as a night signal on its triangulation stations. This lamp employs 

 an 11-in. reflector and, although not as yet fully perfected as to details, it is believed 

 it can be produced 1 to weigh about 24 pounds and to cost under $50, without the dry 

 cells. Eighteen cells are employed to furnish the current and these will give about 

 9 hours' continuous service. A-s used intermittently in signalling they will last a 

 considerably longer period, depending on the amount of such use. 



This lamp has the usual sighting-tube, reading-lamp, and switch-key. Its dis- 

 tinguishing feature is a -specially designed, gas-filled bulb having a highly concen- 

 trated filament which, with a 6-volt, 2<i-ampere current, gives 260.000 ^apparent 

 can<Jle-power at 100 ft. The range of this lamp under ordinary conditions is 50 to 



