262 REPORTS ON THE STATE OF SCIENCE.—1914. 
the matter was entirely different, and with this reduced vision motor 
driving would have been full of difficulty and danger by reason of the 
reduction of the range of vision. When, however, I lowered the vision 
to 6/18 partly navigation and motor driving would have been dangerous 
by night or day. 
The experimental evidence obtained by the Expert Committee at 
Shoeburyness was to the effect that vision of less than 6/12 seriously 
affects colour perception, and that consequently 6/12 represents the 
minimum of vision compatible with safety. This accords with my own 
personal experience, with the reservation that anyone who possesses 
6/6 vision will be a much safer navigator, other things being equal, 
than anyone who possesses 6/12 vision. 
Mr. Fergus seems to draw a distinction between myopia and hyper- 
opia, but when I have rendered my vision defective by rendering my 
eyes hyperopic—that is, by the wearing of concave spectacles—I have 
been unable to detect any practical difference in the result. In both 
cases one makes many failures when one’s colour vision is tested by 
the lantern. When the aperture is small and the light a little dim, 
no colour can be seen at all, probably for the reason that Sir William 
Abney instances. 
In Sir Wiliam Abney’s work, dated 1913, ‘ Researches in Colour 
Vision’ (p. 409), reference to similar experimental work is made. 
The writer, a few years ago, when considering other causes than those 
of deficient colour sensation which might prevent the recognition of 
colour, came to the conclusion that the optical condition of the eye 
might be of such a nature that small discs of coloured light might be 
taken as colourless or not seen at all. To confirm or disprove his 
diagnosis he made his eye myopic and observed a ship’s light from the 
sea-coast and also known stars, and found that with about half normal 
vision the ship’s light at two miles was sometimes invisible or colour- 
less, and that only stars above the fourth or fifth magnitude could make 
any impression on the retina. 
Conclusion. 
There is abundant evidence to show that a number of disasters by 
land and sea are attributable to defective vision. There is also good 
reason for thinking that a larger number of accidents have occurred 
which have not been reported, and, as Mr. Nettleship says, they never 
will be reported under existing conditions. It is clear that, so long as 
the present mode of lighting ships and the present method of using 
railway signals are continued, form vision below 6/12 is dangerous 
as regards its effect on colour perception, and is dangerous by reason 
of the limitation of the range of vision in dull light, and I am of 
opinion that for the purposes of safety the minimum visual require- 
ments should be 6/9 in one eye and 6/18 in the other. A hyper- 
metropia of two dioptres with astigmatism not exceeding ‘75. D might 
be permitted. The colour vision should be normal and tested both with 
wools and lights, and there should be no ocular disease. To satisfy 
these requirements it is necessary that all those who go to sea or 
enter the railway service to earn a livelihood should be examined at 
