DUANE— SIGHT AND SIGNALLING IN THE NAVY. 40i) 



throwing dots and dashes of hght against a cloud. Such signals, 

 which are the same as winker-light signals, can be seen and read 

 practically any distance. 



6. Ardois Signals. — The Ardois is not as fast as the semaphore, 

 but faster than the winker light or wig-wag. The signals are easily 

 seen and easily read. Observers differ a good deal as to the range 

 of visibility of the Ardois — some alleging that it can not be read 

 more than three miles under the most favorable conditions, others 

 that it can be seen from four to six miles. This is with the electric 

 lamps on shipboard which are slung twelve feet apart. In some ex- 

 periments that we made at our Fire Island signal station during the 

 Spanish-American War, similar lamps lighted by acetylene were 

 read eight miles. 



At long distances the several lights of the display run together 

 into a continuous bar, but even then it is possible to read the signals 

 by noting whether the bar is long or short and whether it is plain 

 red or plain white, or white beaded with red. The red light 

 naturally looks smaller and dimmer than the white, and it would 

 doubtless be an advantage if the red lamp were made larger and of 

 more candle-power so as to equalize the visibility of the two. 



The x\rdois displays may be obscured by funnels, masts or other 

 interventions ; and it sometimes happens that in the complex of wires 

 that go from the keyboard to the lamps some part will give out, so 

 than one or more of the thirty combinations is defectively given. 



The Ardois makes very little tax on the eyes. 



7. Flag Displays. — Flags of battleship size can be read six miles 

 or more by a practiced observer. This, however, obviously depends 

 on many factors — the clearness of the atmosphere, the direction of 

 the sun,'^ the way the flags blow out in the wind,* the character of 

 the background, etc. The colors used are white, red, blue, yellow, 

 and black (the last in only three of the flags). White is by far 

 the most conspicuous color, and in the party-colored flags may be 

 the only part visible. Some, in misty days or at dusk, find difficulty 

 in discriminating between certain flags like L and U but the experts 

 say they never have trouble on 'this score. 



' Sun behind flags interferes very seriously with the ability to read them. 

 '^ A little flapping enhances the legibility of the flag; a good deal of flap- 

 ping impairs the legibility. 



