DUANE— SIGHT AND SIGNALLING IN THE NAVY. 413 



It also causes visual discomfort which may after a time result in 

 visual disability. The causes of this discomfort, as Feree has 

 ])ointed out, are sudden dilatations and contractions of the iris, con- 

 junctival irritation, and fatigue of the exterior eye muscles. 



The effect of slow or imperfect adaptation on signalling effi- 

 ciency has not, so far as I know, been examined scientifically. It 

 would seem as if this were a promising field for the physiologists, 

 psychologists, and our naval medical men. 



7. Effect of After-images. — After-images conceivably may be a 

 cause of confusion in signals by night semaphore, by winker light, 

 antl by flashlight — and possibly by Ardois. That they have this 

 effect is doubtful, but the case requires study. 



8. Effects of Ocular and General Fatigue. — It is obvious that to 

 do signal work as it should be done, the signalman must be con- 

 tinuously alert and mentally and physically quick. He must not 

 only be all the time in a state of physical efficiency, but must have 

 a good store of surplus energy so as no time to be close to the limit 

 of his resources. Usually this desirable state obtains, for in the 

 first place our seamen are picked men — physically fit and mentally 

 alert. In the second place, life on board ship is stimulating and 

 wholesome to mind and body, and tends to keep men constantly in 

 good condition. 



One serious drawback is to be noted. Reference has been made 

 more than once to the fact that our navy is undermanned. The re- 

 sult is that even in the ordinary routine work the men have to work 

 overtime, and when doing high pressure work, as in performing 

 evolutions or target practice, they may have to work almost con- 

 tinuously for many hours at a time. No body of men, however fit, 

 can keep up continuously under such a strain. Efficiency in all 

 directions is impaired, and, not least, efficiency in signalling. 



Conclusions. 



From these desultory observations the following conclusions may 

 be drawn. 



I. The standards of vision and color vision now required in the 

 navy should by no means be diminished, but rigorously maintained. 

 It would be well if equally high and rigid standards could be applied 

 to the army. And it becomes us as laymen to uphold in every 



