VISUAL REQUIREMENTS OF SAILOR AND RAILWAY EMPLOYEE. 261 
such absence shall have extended for six calendar months or upwards, 
such pilot shall not return to duty unless and until, as regards his 
condition physical and mental, a medical practitioner and, as regards 
his vision and eyesight, an expert oculist, to be in both cases nominated 
by the Marine Board, have respectively certified to the Board that such 
pilot is in a fit condition physically, mentally, and visually to perform 
his duties as a pilot.’ 
The annual examination of the pilots has probably averted disaster, 
as one pilot was retired with high blood-pressure and retinal hemor- 
rhages detected in the course of periodical examination. 
The Union Steamship Company of New Zealand adopts a like 
standard for those who enter its service, and provides for periodical 
testing of form vision. 
What standard of form and colour vision is necessary for safe 
navigation or railway service? 
So far as colour vision is concerned the results of the ordinary tests 
with wools and lanterns seem to coincide with the quantitative measure- 
ments made by Sir William Abney, and I have never seen any prac- 
tical difficulty in detecting a dangerous degree of colour defect by the 
combination of these means. 
With regard to form vision, however, the matter is not nearly so 
simple. Two questions arise: What standard of form vision shall be 
required? and, Are two eyes necessary? Some time ago, in the 
Ophthalmic Review, Mr. Fergus gave an account of his own experi- 
ence in motor navigation with defective vision. Apart from theoretical 
disquisition which I was unable to follow, he stated correctly enough 
that lowered form vision means for the most part a loss of detail. A 
house is still seen as a house at a distance when the form vision 
is lowered, and a ship is still seen as a ship in like circumstances. I, 
however, set to work to make myself artificially myopic with bi-convex 
glasses, and to reduce my form vision to different degrees in order to 
repeat his experience. In passing, however, it should never be for- 
gotten that the standards given by Snellin’s types are at best approxi- 
mate. They depend on the illumination of the types, on the contrast 
between the letters and the background, on the illumination of the 
room, and the size of the pupil. They nearly always give better results 
in daylight than by artificial illumination. At best they have approxi- 
mate significance. 
_ Rendering my eyes artificially myopic in this way, I reduced my 
vision to 6/9 partly and 6/12, and found, as Mr. Fergus said, that 
houses, men, dogs, and objects of various kinds were still recognised 
as such, but certain details could not be detected. For example, a 
man and a dog at five hundred yards’ distance were seen as one mass; 
a flag on a flagpole at a distance of a mile was indefinite, so that one 
could not tell which way the wind was blowing. Outside Dunedin 
Harbour I mistook a ship on the rocks for the rocks themselves. By 
bright ordinary daylight I should have experienced little or no difficulty 
in navigating. Furthermore, in a long motor run there was not the 
least difficulty in seeing details on the road, and there would have been 
no difficulty in steering the motor. At evening, however, and at night, 
