408 DUANE— SIGHT AND SIGNALLING IN THE NAVY. 



ships being forty miles apart. The messages are very legible and 

 the method not taxing to the eyes. 



J. Hand Semaphore. — This has largely replaced wig- wag, be- 

 cause the signals can be made faster. I am a tyro at it myself, and 

 for that reason, perhap, it seems to me more difficult and less leg- 

 ible than the wig- wag. It certainly requires careful technique, 

 otherwise certain combinations are indistinguishable from each other 

 (e. g., O from I and W from X). It is said that a good observer 

 can read signals three or four miles, but this depends greatly on the 

 sender and the background. 



4. Machine Semaphore. — By day the semaphore arms are read- 

 ily seen if the background is good. By night the lights on the two 

 arms are apt to blend in the acute angled signals (H, O, T, W, Z), 

 making it somewhat difficult to determine whether one or two arms 

 show. This difficulty does not obtain when a field-glass is used. 

 If the night semaphore is worked rapidly, the after-images pro- 

 duced by one display might theoretically be confused with the dis- 

 play following, but this seems not to occur. The shifting lights are 

 somewhat trynng to the eyes of the inexperienced. The range of 

 legibility is variously stated at one to three miles or more. 



5. Winker-Light. — This, like the heliograph which it greatly re- 

 sembles, can be seen practically any distance, provided the sender 

 or receiver is sufficiently elevated above sea-level and intervening 

 obstructions. If the technique of sending is good, the light-flash can 

 be read as far as it can be seen. In India, where sending can be 

 done from great elevations, the heliograph, they say, can be read a 

 hundred miles. I have signaled with it sixteen miles. It might be 

 used that far on shipboard. To do so would require both observer 

 and sender to be rather more than forty feet above sea-level. 



The winker light is quite trying to the eyes, especially when re- 

 ceived through a glass, and beginners cannot receive long at a time 

 without their attention flagging and their work being unreliable. 

 Twinkles and flashes'' impinging in rapid succession on a partially 

 dark-adapted eye, cause considerable strain, although it is a strain 

 to which one does get remarkably accustomed. 



Just as the searchlight is used for wig- wag it is also used for 



^ Readers of Kipling will recall his graphic lines : 



" A heliograph tempestuously at play." 



