NIGHT SIGNALLING 185 



75 miles, no telescope being employed, while under exceptionally favourable condi- 

 tions of atmosphere it has been seen with the naked eye at 100 miles. On a dull day 

 it can be used up to 10 or 15 miles. As with other electric lamps, the speed of 

 sending is somewhat reduced because the filament requires an appreciable time to 

 heat up and cool off. About five words per minute can be sent efficiently. 



This lamp with the large number of dry cells required for its operation is not a 

 rea'dily portable equipment and would only be suitable for permanent stations. Diffi- 

 cult accessibility would indicate a necessity for employing either wet batteries or the 

 inert type of dry cell, in preference to the ordinary type. 



2 USE IN FOREST PROTECTION 



Thus far the only use made of signal-lanterns for forest-communication purposes 

 has been on an experimental basis by the United States Forest Service in the state 

 of Washington. Certain advantageous uses for aii efficient lamp for lookouts are, 

 however, apparent. The ease with which lamps may be used by one man, requiring, 

 as they do, no adjustment after once being properly aligned, makes them especially 

 valuable for training operators to send and receive flash signals, and for assisting 

 trained men to keep in practice. Of course, the signal-lantern as a means of lookout 

 communication is subject to nearly the same general limitations as is the heliograph, 

 and it cannot be considered as the principal communication equipment on important 

 stations in preference to the telephone, nor can it be depended upon to replace the 

 heliograph. Practically all fires are detected during the day and where visual signals 

 a^e depended upon for communication the principal methods must be available for 

 daylight operation. 



Signal-lanterns, however, can be operated from towers, while heliographs cannot, 

 and, owing to the more uniform conditions that prevail at night, they are the most 

 reliable of all means of visual signalling. 



Although, as stated, the use of signal-lanterns in forest protection is as yet very 

 limited it would seem that a lantern with sufficient range would find the following 

 application : 



1 To serve about the same purposes at night that the heliograph and flag serve 

 during the day, that is, to afford communication on lookout stations before the instal- 

 lation of the telephone, during temporary interruptions of telephone service, or on 

 intermediate temporary stations which are not of sufficient importance to justify 

 the provision of telephone equipment, or stations being occupied experimentally. 



2 To serve as a specially convenient instrument for training and practice in the 

 sending and receiving of flash signals. 



3 To make possible the speedy report of fires detected just before sunset. These 

 are particularly numerous in regions where much land clearing is going on. 



4 To make possible the speedy report of such fires as are detected at night. Night 

 detection is, however, rare. 



5 On a dull day when the heliograph cannot be employed the lantern may be 

 used for short-range communication. With the Fischer lamp, daylight signals may 

 be sent about 10 miles. 



6 To report at night, fires that were detected during the day but could not be 

 reported immediately because lack of sunlight prevented the operation of the helio- 

 graph. Also, messages not urgent in character, such as orders for supplies, personal 

 messages, etc., may be sent at night. 



The signal-lantern is inferior to the heliograph in the following respects: 



1 Its daylight operation is very uncertain and very limited in range. 



2 It cannot be used for communication with a moving patrol because of the 

 practical impossibility of picking up stations at night unless their position has been 

 determined and sighted Upon before nightfall. 



