ULTRA-VIOLET SUNLIGHT
IN Ancient Egypt there was the plague. of darkness which could be felt. In Modern England there is the plague of darkness which can he smelt, in our cities of dreadful day. In Egypt and, if we will, in England there is the paradox of light which cannot be seen. We call it ultra-violet light because, in the ethereal gamut, it lies beyond the violet or upper end of the octave of notes which our eyes are capable of seeing. This octave is only one of more than fifty already well known and defined by physicists : extending from the longest waves used in " wireless "—perhaps ten miles long—tO the hardest X-rays, the gamma rays of radium, and even those, shorter still, which have lately been discovered by Professor Millikan in California. Of these many octaves the solar radiation includes not a few. SoMe, below the visible octave (of which the lowest note is red) we call infra-red or heat rays. Enough of these is a feast : but enough we must have. There are several octaves of ultra-violet and the highest-pitched would be There is, of course, after untold aeons of creative evolu- tion, _ tion, the most exquisite and perfect adaptation between our needs and the exact range and intensity of the solar radiations' as' they reach us on the floor of the atmo= spheric ocean in which we live. Almost' exactly half an octave above the visible violet we find the wavelengths which. comprise the vital rays, as we may well call them, without which our earth would be but a sterile cinder. The undesirable wavelengths, from which the atmosphere so perfectly screens us, are produced abundantly by many modern lamps, designed for medical and hygienic pur- poses. Once again, therefore, I issue a general warning against 'the careless use of such ill-devised or risky lamps; and a plea for the contention that sunlight and nothing else is the model and pattern to follow, if possible, when these lamps are devised. There is very much to say on this' subject, for doubtless every modern house should have an " artificial sunlight " lamp, such as I once de- scribed in the Spectator. Also there is the various use of various types. Thus I also have a weak lamp, looking merely like a rather large electric light bulb; which differs in that' the filament contains tungsten, a powerful emitter of ultra-violet rays when it is incandescent, and also in that the bulb is made of quartz, which transmits the ultra-violet rays. When I happened to have a broken leg and knee and a very septic wound of the hand, I used this lamp upon my lesions for hours at a time. It is employed in clusters for apes, marmosets and other animals at the Zoo, and has served them unprecedentedly during the past winter. Readers should send is. 14d. to the Sunlight League, 37 Russell Square, W.C., for No. 2 of Sunlight, where they will learn much, very pleasantly hut accurately, on this question of lamps. But our present concern, in the returning light of the spring, is bigger and better than that. - We read of sunlight and of ultra-violet light, but the precise phrase used as the title of this article is not familiar. Yet ultra-violet sunlight is exactly the most precious and necessary item of the physical universe for our lives, and it must be recognized and preserved accordingly. In nearly a quarter of a century of persistent propaganda on this subject, I have never used the word sunshine, for ultra-violet light does not shine, and sunshine not aceom- pained, as it always is in unspoilt Nature, by its comple- ment of ultra-violet light, has no medical nor hygienic properties. (This is by no means to say that heat rays and the visible octave are useless : but their use is in combination with ultra-violet light. " Man shall not live by bread alone . . ") It is the ultra-violet part of sunlight that is antiseptic. Without it sunlight cannot cure, or prevent rickets nor tan the skin nor enrich the blood. It is the first and most arrested by smoke, clothes and ordinary glass. None reaches us from the sun behind ordinary window-glass, none from an incandescent electric filament, such as we use in our houses for lighting, through the glass of which the ordinary bulb is composed.
We are persistently fooled by, the fact that our eyes are blind to this creative boon without which there would be no eyes to see at all. Thus, in estimating sunlight, we interest ourselves in the visible rays, or even in the heat rays, and use means of the type represented by a boy's burning glass in order to measure the presence and intensity of what we call sunlight. The presence or absence of the ultra-violet does not interest us, and the facts escape us. The most misleading data are collected and published as if they were of final and conclusive value, though in fact they miss the point. In 1890 in his now classienl.paper on-rickets t and sunlight, Dr. T. A. Palm— still visiting his patients in Kent—asked that all our cities should measure the actinic or chemical—i.e., ultra- violet—rays of the sun rather than its heat. Thanks to the American bibliographer who directed my attention to this paper in New York some years ago, and to the Committee on Light appointed by the Medical Research Council early in 1922, we have begun to do, in just one or two places, what Dr. Palm asked for a generation ago. A few readings are recorded under the weather report in the Times every morning. The marked contrast, almost every day, between Kingsway, Hamp- stead and Peppard in Oxfordshire, close to London, shows how deplorably and thoroughly the smoke of London robs us of ultra-violet light. The method used is simple and delicate and we owe it to the Committee above-named and especially to Dr. Leonard Hill, F.R.S., one of its members. Only the estimation of ultra-violet light shows us what our urban smoke really costs in respect of sunlight. Readings commonly made and quoted in a letter to the Spectator of April 3rd are of no present interest or significance. They are of the nature of eyewash, ignoring what the eye cannot see. If our industrial cities daily recorded their ultra- violet sunlight, or lack of it, and if our south coast health resorts, for instance, did likewise, we should begin to learn, at long last, what it means to pollute our skies, even by particles too small to stop the visible sunlight but large enough to stop the tiny vital rays of ultra-violet. 1 challenge all our•industrial cities, not least when, according to their custom, they prepare their defences against Mr. Chamberlain's Bill for Smoke Abatement, to record their ultra-violet light, if they dare —as indeed not one, I believe, yet does : and - I warn the nation against records which our pioneer Dr. Palm showed to be irrelevant thirty-six years ago, because they do not record the ultra-violet sunlight which makes our earth a home of life.
CRUSADER. .
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