256 REPORTS ON THE STATE OF SCIENCE.—1914. 
spots, produced by x rays on the luminescent screens after long 
exposure, may he destroyed again by exposure of the screens to day- 
light. You may also explain the peculiar medical observation that 
therapeutic radium effects in parts of the human body not covered, 
specially in the face, are often not of long duration—for the face is 
exposed to the counteracting visible rays of daylight. 
We notice here a connection of our subject with a department of 
great practical importance. For all therapeutic effects of a rays, 
radium rays, and mesothorium rays would, according to this view, be 
effects only of ultra-violet light produced by the stopping of these rays 
in the human body, and the ‘special character of the radium- and meso- 
thorium- and z-ray treatment would consist mainly in the carriage into 
the interior of the body, by the rays, of the ultra-violet light, which 
is not confined to the surface of the body, but is produced at every place 
where any of the entering rays are stopped. You may notice further 
that this view of the medical ray-effects presents a heuristic method 
for the treatment itself, which up to the present followed quite fortui- 
tous and merely empirical paths. For it may be hoped that treatment 
by radioactive substances will be useful in every disease in which ultra- 
violet light has been proved to be efficient in some degree; you will 
avoid such treatment in the well-known cases in which light of short 
waye-lengths is noxious, and you may be justified in substituting an 
ultra-violet light treatment where radium or mesothorium is not obtain- 
able. At the same time it becomes evident why the treatment of certain 
diseases by the # rays has effects very similar to those produced by 
fulguration—that is, by the light of very strong sparks: the efficient 
agent is in both cases the ultra-violet light. : 
But it cannot be a physicist’s task to enter too far in medical 
questions: it was only my intention to show how interesting are some 
of the problems which are connected with the salts coloured by cathode 
rays. 
The Problem of the Visual Requirements of the Sailor and the 
Railway Employee. By JAMEs W. Barrett, C.M.G., M.D., 
M.S., F.R.C.S. Eng. 
[Ordered, on behalf of the General Committee, to be printed in eaxtenso.] 
Tuer discussions which have taken place on this subject are apparently 
interminable. They have for the most part resolved themselves into 
discussions amongst oculists and communications made by deputation 
or otherwise to the Board of Trade presenting their point of view. 
The Board of Trade, whilst it has collected a certain amount of 
valuable information, has not materially modified its methods, and 
apparently does not propose to do so. As its authority weighs heavily 
in the Dominions, which are as a rule not consulted by it before it takes 
action, various anomalies make their appearance. I venture therefore 
to bring before this meeting of the Physiological Section of the British 
Association a summary of the present position. 
