DUANE— SIGHT AND SIGNALLING IN THE NAVY. 405 



but, of course, much more in time of war, the exigencies of the 

 service may be such that the skilled man is not available. He may 

 have to be replaced by a man not sufficiently trained. This is par- 

 ticularly the case under present-day conditions when our warships 

 are deplorably undermanned. It is important, therefore, to consider 

 what difficulties an inexperienced man has to contend with and how 

 these difficulties affect his reading of signals. 



There is another aspect of the matter. There are some men 

 who never become good signalmen. The practice has been to dis- 

 cover whether this is so or not by selecting a man haphazard, trying 

 him out, and rejecting him if he fails. It would be better surely to 

 be able to form some idea in advance of what the causes of dis- 

 qualification are, so that the right sort of man might be picked out 

 in the first instance and no time wasted in training the inefficient. 



From both points of view it becomes us to consider the factors 

 that determine a man's ability to perform signal duty. These fac- 

 tors are: (i) The character of the signals themselves and the way 

 this character is affected by external conditions. (2) The signal- 

 man's own physical and mental qualifications. 



Intrinsic Character of Signals Themselves. 



Signals differ very greatly in : 



/. Visibility. — Some even under the best conditions can hardly 

 be seen beyond two or three miles (by the tyro not so far), others 

 can be seen any distance. 



2. Legibility. — Some signals, especially those having a large 

 number of elements (flag signals) or in which the elements are 

 shown in groups (Ardois) or very rapid succession (semaphore, 

 hand wig-wag), can usually be seen further than they can be read — 

 although it must be stated that this discrepancy between legibility 

 and visibility is most marked with beginners and diminishes rapidly 

 as experience grows. Other signals ( winker light, wig-wag by 

 flashlight or searchlight. Very stars) can be read even by begin- 

 ners as far as they are seen. 



J. Amount of Strain They Impose on the Sight and Attention. — 



also a signalman, when finding himself getting unsteady, will ask a companion 

 by him to take his place. 



