406 DUANE— SIGHT AND SIGNALLING IN THE NAVY. 



This is particularly great with the semaphore and especially the 

 winker light. 



External Conditions Affecting Signals. 



These are : 



1. Faulty Technique in Sending. — ^Mistakes may occur with any 

 method ; but faulty technique gives trouble particularly with the 

 hand wig-wag, hand semaphore, and winker light. It affects visi- 

 bility scarcely at all, but often greatly reduces the legibility of mes- 

 sages. By impairing legibility it puts an added strain on the sight 

 and attention of the observer. 



Faulty technique includes not only carelessness in the mechanical 

 execution of the signal, but also failure to acknowledge signals 

 properly, failure to secure a proper background when requested, 

 failure to correct errors, and too slow sending. Such faults, if 

 persisted in, unduly prolong the message and weary the receiver. 



2. Weather Conditions. — These naturally affect both visibility 

 and legibility, especially the latter. Flag hoists and Ardois become 

 particularly difficult to read in thick weather and m^y have to be 

 replaced by distance signals or even by sound signals. Flag signals, 

 if the ship is not under way, require some breeze for their proper 

 display ; but a gusty wind may interfere a good deal with their 

 legibility.* The sun, if behind the observer, is usually a help espe- 

 cially in hand wig-wag, hand semaphore, and flag displays. The 

 light shining on the display and reflected from it, makes the signal 

 stand out better, especially when the latter is in motion or shows 

 contrasting colors (hand wig-wag, hand semaphore, flag signals). 

 Per contra, the sun behind signals not only tends to drown them out 

 so that they are hard to read, but also causes so much irritation and 

 dazzling as the result of glare, that the eyes may soon tire and be- 

 come unserviceable. 



A strong wind blowing in the observer's face may make the eyes 

 water and so interfere with the reading of signals. 



5. Use of Field Glass. — Some signalmen prefer to use the naked 

 eye, but many habitually use either a spy-glass or generally a low- 

 power field glass. This about doubles the distance at which sig- 

 nals can be read and increases the legibility of some signals, espe- 



4 For the tyro at least. The older and more experienced man will find 

 little trouble on this score. 



