SIGHT AND SIGNALLING IN THE NAVY. 



By ALEXANDER DUANE, M.D. 



(Read April jj, 1916.) 



Perhaps a better title for my paper would have been " Desultory 

 Notes of an Ophthalmologic Signalman." Such a title, moreover, 

 would indicate the paper's only excuse for being. For desultory 

 as the notes unfortunately are, the author has felt that they might 

 be of some service because, being both an ophthalmologist and a 

 signalman, he had a somewhat unusual advantage in studying the 

 subject. As an ophthalmologist, he had been concerned with the 

 observation of visual phenomena and knew something of the phys- 

 ical and psychic factors underlying them ; while as a signalman, quar- 

 termaster, and signal officer in the naval militia and navy, he acquired 

 a practical acquaintance with the various forms of naval signalling 

 under service conditions. 



In considering the subject it is important to have some idea of 

 what constitutes naval signals and to know in general how they are 

 made and interpreted. 



For the purpose of this paper, signalling may be defined as the 

 art of communicating with another person by means of symbols 

 other than written or spoken words ; such symbols consisting, ac- 

 cording to the method employed, of shapes, lights, sounds, move- 

 ments, or any sort of exhibit whatever that can be appreciated at a 

 distance. These symbols, either singly or combined in groups, are 

 use, according to some special system, to denote individual letters, 

 digits, or other characters ; and these characters in turn are com- 

 bined according to some preconcerted code to form messages. 



The special symbols employed in any one system are called the 

 elements of that system ; and the system is said to have 2, 3, or 10 

 elements, according to the number of different kinds of symbols 

 used in it to form the letters or characters. Thus a signal consisting 

 of a display of lights vertically over one another at a ship's mast is 

 said to be made by the Ardois Method. It is made with two ele- 

 ments, since only two kinds of symbols (viz., red and white lights) 



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