412 DUANE— SIGHT AND SIGNALLING IN THE NAVY. 



balance. These defects cause much the same trouble as refractive 

 errors. That is, they cause undue strain and hence may ultimately 

 produce temporary disability of the eyes as the result of prolonged 

 fatigue of the eyes and the body. It would be well to put candi- 

 dates for signal work through a careful examination for these 

 errors, and, if they are present, put the candidate himself on pro- 

 bation or in extreme cases reject him altogether for signal work. 

 Of errors of this sort it may be remarked, first, that confusion 

 due to them is revealed by the fact that it disappears if one eye is 

 shut ; second, that troubles of this sort may be accentuated or con- 

 verted from latent into positive sources of mischief by some of the 

 conditions of naval service, c. g., by the too prolonged use of a spy- 

 glass which excludes one eye from vision. 



5. Slotv Reaction Time. — In the complex process of seeing, inter- 

 preting what is seen, and expressing or acting on the interpretation, 

 a certain time is consumed, which difl:'ers in different people. In 

 certain avocations it is important that this time be reduced to a 

 minimum. For a railway engineer, a motor driver, a pilot, a gun- 

 pointer, or a signalman this need is imperative. This is well recog- 

 nized in the navy, where a man, no matter how keen-sighted, how 

 intelligent, or how steady, is rejected for gun-pointing or for sig- 

 nalling, if on trial he is found to be persistently too slow. A man 

 must be sharp in all his reactions, " quick on the trigger," as they 

 say. Such men fortunately are fairly numerous in our navy, con- 

 taining as it does bright, active, and wholesome youngsters, abound- 

 ing in physical energy and spirit. Even among these, however, 

 there may be some who do not react quickly enough to be good 

 signalmen. Would it not be well to weed these men out by psycho- 

 logical tests of their reaction time, taken when they are first detached 

 for signal work, rather than, as at present, to find out by weeks of 

 useless trial that they are too slow? 



6. Sloznj Adaptation. — A signalman's work on shipboard requires 

 quick adaptation. With varying sunlight, the glare from water and 

 bright work, lights below decks of varying intensities, signal lights, 

 ship's light, and searchlights, he is often required to change sud- 

 denly from one condition of illumination to another. This change 

 requires quick retinal adaptation, as otherwise there may be confu- 

 sion in seeing with a retina ill-adapted to the existing illumination. 



