THE HELIOGRAPH 161 



purposes during only a limited portion of the day. "While their dependability for 

 sending purposes may be high, they are not adapted for receiving messages except 

 during the periods when they are actually occupied. Such periods may be regular or 

 not, according to the facilities and organization in each case. 



Temporary stations are those established by moving patrol or other moving units 

 of the forest force merely for the purpose of communicating with some other station 

 in the forest. As a rule they will be used for sending messages only and will have 

 little or no value as receiving stations, since they will seldom be occupied regularly 

 but will generally be established only as the moving unit finds it necessary to com- 

 municate with headquarters or some other station. 



It is obvious that in the first two cases the element of easy portability is of much 

 less importance than in the third. At the most, a heliograph outfit, even of the largest 

 size, is quite easily carried by one man, so that where it is simply a question of setting 

 up an instrument in a suitable location at a permanent or semi-permanent station, 

 any of the usual types may be employed. No special heliograph equipment is there- 

 fore needed for lookout or headquarters use but, as rigidity is an element of some 

 importance and as range is governed by the size of the mirror, one of the heavier 

 models should be selected and the size determined by the ranges over which it is desired 

 to work. 



When,however, the heliograph is to form a part of the outfit carried by a foot 

 or horse patrolman the question of size and weight becomes extremely important. 

 Such patrolmen are usually loaded to their carrying capacity with tools and supplies 

 requisite for their work, and every item of their equipment must be reduced to the 

 lowest practicable weight. The ordinary military heliographs even of the smaller 

 sizes are too heavy and too bulky to be made a part of the outfit of either a foot patrol- 

 man or horse patrolman, though they might be used by canoe patrol where few portages 

 are necessary, and may be easily carried on any wheeled vehicle used in forest protec- 

 tion except a motor-cycle. This difficulty would seem to be successfully overcome by 

 the new Godwin heliograph described herein. 



In general the heliograph will find useful application to forest protection inter- 

 communication in the following ways: 



(1) Before the construction of the telephone system, to furnish communication 

 facilities to all parts of the forest. 



(2) As a substitute for an emergency telephone line, operating from temporary 

 camps to lookout or other permanent stations on the main telephone system. 



(3) As an emergency equipment at all permanent lookout stations to ensure against 

 isolation of the station in the case of a break in the telephone line. 



(4) As a cheap substitute for a telephone on secondary lookout points occupied 

 during a limited portion of the fire season or during an unusually dry season only. 



(5) As a cheap substitute for a telephone on lookout peaks which it has not yet 

 been decided are entirely suited for permanent occupation. 



Section 100 Range and Speed 



The range over which the heliograph can be operated depends on the size and per- 

 fection of the mirror, the brightness of the sun, the clearness of the atmosphere, and, 

 to a much smaller degree, upon the angle at which the light is reflected from the mirror 

 and the background against which the signals are seen. While the normal working 

 range of the 4|-in. square or 5-in. round mirror heliograph is about 40 miles, either may 

 be read by the naked eye under ordinary conditions at 50 miles without difficulty, and 

 up to 90 miles with a glass. In the clear atmosphere of the West, ranges of 100 miles 

 have been accomplished. For longer ranges a larger mirror is required. With an 8-in. 

 square mirror signalling has been carried on in Arizona between stations 186 miles 

 apart. Practically, signals may be exchanged between any two points which are inter- 

 visible, regardless of their distance apart. Intervisibility will depend on their distance 



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