ULTRA-VIOLET TESTS

Greymouth Evening Star, 17 January 1928, Page 3

ULTRA-VIOLET TESTS

SCIENCE KILLS SHAMS.

:1 At the end of the Great War Prol, jfessor R. W. Wood, that genius among t American physicists, came to a meet--3 :ing of the London Physical, Society !- land revealed the methods of invisible i signalling used by his countrymen - in fighting the enemy. He showed 1 a telescope in which a six-volt lamp 1 was hidden. The telescope was closed 5 by means, of a piece of special glass which allowed only the ultra-violet ' rays to pass, arid was focussed on a I distant point where the beam project--3 ed by it was received in a similar tele- • scope provided with a fluorescent 3 screen. Morse signals could thus be 1 sent over a distance of six miles, quite I unknown to the enemy, since the sig--3 nals were only revealed by the flashes on the fluorescent screen itself (says E. E. Fournier d’ Albe, in the “London 1 Observer”). 1 The phenomena of fluorescence were discovered as long ago as 1833 by Sir 1 David Brewster, who found that when quinine is dissolved in sulphuric acid the solution exhibits a beautiful blue colour under the influence of the rays which lie beyond the violet end of the spectrum. In the matter of sensitiveness the human ear and the eye are in strange contrast. While the ear can hear all sounds capable of penetrating the atmosphere from the twenty-foot soundwave of the deepest pedal note to the shrill half-inch wave of the bat’s cry, the longest light-wave perceived by the eye is barely twice as long as the shortest.. The secret lies no doubt in the long evolutionary process by which the eye has accommodated itself to the rays of sunlight, which have a maximum energy in the yellow-ish-green portion of the spectrum, a region which exactly coincides with the maximum sensitiveness of the human eye. From this circumstance we may conclude that the planets revolving round other stars ' may harbour living beings with eyes sensitive to the infra-red or ultra-violet rays, according to the lower or higher temperature of their central orb.Tire exploration of the hidden region of the spectrum has been a fascinating pursuit, not unattended by risks. We have gradually traversed the ultra-violet right down to the most penetrating X-rays, which have a wave length five hundred times shorter than light. We all know the fate that has overtaken many brave pioneers of this exploration, but we can be sure that no danger will deter scientific investigators from searching the Unknown.

The ultra-violet of the mercury arc produces a kind of snow-blindness, which, however, soon wears off. But it has an extraordinarily diversified effect on different substances. In uranium glass it produces mrich applegreen fluorescence; a tallow candle blows bright blue and the human body appears a faint purple. The teeth fluoresce brilliantly, but in order to do so they must be alive. False teeth remain unilluminated. The late Sir William Crookes once started a brilliant assembly at the Royal Society by offering to test diamonds then and there by means of ultraviolet rays, relying upon-the fact that none but a real diamond shows the characteristic phosphorescence. Even butter and margarine can be distinguished by their different appearance! in ultra-violet light. The deciphering of the original writing of a palimpsest by photography was a much admired feat of the early eighties. This was, however, done by simply excluding all but the violet rays from the negative. The great flood of ultra-violet light yielded by the Cooper-Hewitt mercury arc has vastly extended this field of exploration, and the exhibition given by Dr Herman Goodman at a New York electrical exhibition showed some novel applications of the principle, though I cannot take the alleged testing of bootleg whisky seriously. There is no doubt that every advance into the invisible regions of the spectrum will yield fresh revelations. Already Pickering has discovered signs of a fugitive vegetation on the moon and Hale has found the extraordinary mantle of calcium cloudlets which covers the sun. Mr Baird reveals —somewhat unkindly, perhaps —how people appear when under infrared illumination. The invention of a “machine with a moral sense” is a chimera, but the best way to stamping out sham is to make their detection easy and inevitable.