168 



METHODS OF COMMUNICATION FOR FOREST PROTECTION 



as the screen is entirely separate. On the other hand a single operator is in a much 

 better position to control the adjustment for sun motion during signalling when using 

 the British type than when using the American. This is because he can have both hands 

 on the two adjusting screws constantly, as one of them is used as the key to elevate 

 the mirror. This is important as the adjustment 'for sun motion is needed at extremely 

 short intervals and is often a serious handicap to one man when using the American 

 Army heliograph. The fact that an extra screen and tripod is required for the 

 American instrument is of little importance in station use and is more than offset 

 by the disadvantage of the greater number of small parts in the British models. The 

 latter also are more subject to difficulties in signalling caused by vibration in high 

 winds. This is serious, because most lookout stations are located where winds of con- 

 siderable violence blow more or less constantly. It is believed that for the best possible 

 results under all conditions a combination of the British type of instrument with the 

 American form of screen will give the greatest satisfaction. ' The screen should be 

 used only when vibration or other troubles render it necessary. It is to be noted, how- 

 ever, that this is a rather expensive equipment and would cost about twice; as much 

 as the Forest Service instrument alone, this last being considerably the lowest-priced 

 heliograph on the market. 



Heliographs cannot be successfully employed on lookout towers. The reason is 

 that nearly all such towers vibrate excessively both as a result of wind and from the 

 movements of the operator on the platform. This vibration makes it impracticable 

 to keep a heliograph in adjustment. A platform on top of a lookout cabin or ranger 

 station if rigidly braced may be sufficiently free from vibration to be successfully 

 occupied for heliograph communication. 



IOMI. 



B oundary of California Notional 



-^^r- Telephone lines in operation (Season 1912) 

 Main Lines of Heliograph Com mum 'car ion 



Q Heliograph Centra/ Control Star ions 



O He/Jogroph Substations 



V Forest Supervisor's Headquarters 



District" Rangers Headquarters 



Fig-. 104 Map of California National Forest, showing heliograph system . 



Heliograph stations on mountain lookouts will generally be the most important in 

 the forest, and this use of the station should always be considered when equipping 

 a forest with a lookout fire-detection system. Direct communication between as many 

 stations as possible should be aimed at, and in addition one or more such stations 

 should be arranged to communicate with important headquarters on the. lower levels 

 which may be joined to the telephone system. An example of this kind is shown in 

 Fig. 104. 



