192 



METHODS OF COMMUNICATION FOR FOREST PROTECTION 



by nearby objects. It may be erected on the roof of a cabin and operated from inside 

 if desired, or if placed on top of a tower it may be operated from the ground. The 

 arms are flat boards which must be at least 3 ft. long, and these must increase 1 ft. 

 in length for each mile over 3 miles at which the semaphore is to be read. As 10-ft 



Fig-. Ill The semaphore alphabet, numerals, and special signs 



arms would probably be about the maximum size that could be erected and manipu- 

 lated at a forest patrol or lookout station, the range would be limited to 10 miles. 

 The width of the arms should be one-sixth of the length. The arms are moved by 

 a system of levers, ropes, and pulleys. The levers are placed at or near the base of 

 the pole bearing the arms and may reproduce the position of the arms themselves. 

 If the semaphore is to be read from only one direction, the apparatus should be fixed 

 so that the arms move in a plane at right angles to the line connecting the two 

 stations. If it must be read from various directions, it is necessary to place the 

 arms on a revolving shell or casing surrounding the fixed pole and 1 provided with 

 roller bearings >at the base; or the supporting pole may be set on a ball-and-socket 

 joint to permit of rotation. For signalling by the semaphore method, only two arms 

 are required and these are fixed on the same pivot near the top of the upright pole. 

 The letters are made by the position of these two arms just as when using flags held 

 in the hands. In addition to the two movable arms it is necessary to have a third 

 shorter fixed arm called the "indicator." This arm is placed on the right of the 

 sender, the left as viewed by the receiver. The code is the same as used with hand 

 flags and is illustrated in Fig. 112. 



