DUANE— SIGHT AND SIGNALLING IN THE NAVY. 411 



as lookout, I had a half hour of concentrated misery, since I was 

 absolutely uncertain whether the dancing spots on the horizon were 

 lights to be reported or mere ignes fatui. Certainly I was not quali- 

 fied to be " the eyes of the ship " that night. 



2. Defective Color Vision. — Obviously a signalman must be free 

 from even slight defects of color perception. It is his business to 

 deal with colors (red, white, and green lights, and various colored 

 flags) seen often in the most unfavorable atmospheric conditions. 

 It is fortunate that our navy like all others recognizes the impera- 

 tive necessity that every man in it should be free from color defects. 

 It clings, to be svu'e, to the outworn Holmgren test with wools, 

 when experience has shown that it would be better to use the equally 

 simple and more certain tests of Nagel and of Stilling, as well as 

 the very practical lantern tests. Still our medical officers are very 

 keen in this regard, and it is very rarely the case that any man with 

 color defects slips by them. Moreover, in signal training, the pres- 

 ence of any serious defect would soon show itself by some failure 

 in reading Ardois signals and especially in making out certain flags 

 at signal distance. 



J. Refractive Errors. — Moderate uncorrected refractive errors — 

 hyperopia and astigmatism of a dioptry or so — are quite compatible 

 with keen sight. Eyes affected with them, however, may give out 

 under prolonged strain either of the eyes themselves or the whole 

 body. This has been seen in the European war, in which, as noted 

 by two English observers, men with only a minimum amount of 

 hyperopia suft'er such deterioration of sight from the prolonged 

 strain and fatigue of trench fighting that they become useless as 

 marksmen. In view of the very exacting demands made on a naval 

 signalman, and in view of the fact that in our short-handed navy the 

 hours of work of any one man may be inordinately prolonged, it 

 would seem important that men with even slight errors of refrac- 

 tion should be carefully tested under exacting service conditions, 

 and if they show tendency to give out under the strain, should be 

 kept on probation until it is definitely determined whether they are 

 fit for the work or not. 



4. Defects of the Eye Muscles. — No man with an obvious squint 

 would be allowed to enter the navy, but many a man may get in 

 with a comparatively large latent deviation caused by muscular im- 



