HOW SCIENCE KILLS SHAMS.

Otago Daily Times, Issue 20309, 18 January 1928, Page 11

HOW SCIENCE KILLS SHAMS.

ULTRA-VIOLET TESTS. At the end of the Great War Professor R. W. Wood, that genius among American physicists, came to a meeting of the London Physical Society and revealed the methods of invisible signalling used by his countrymen in fighting the enemy. He showed a telescope in which a six-volt lamp was hidden. The telescope was closed by means of a piece of special glass which allowed only the ultra-violet rays to pass, and was focussed on a distant point where the beam projected by it was received in a similar telescope provided wtih a fluorescent screen. Morse signals could thus be sent over a distance of six miles, quite unknown to the enemy, since the signals were only revealed by the flashes on the fluorescent screen itself (says E. E. Fournier d’Albe, in the London Observer). The phenomena of fluorescence were discovered as long ago as 1833 by Sir 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 20ft sound-wave off 1 the deepest p#dal note to the shrill £i n 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 yellowish-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.

The exploration of the hidden regions of the spectrum has been a - fascinating pursuit, not unattended by risks. We nave gradually traversed the ultra-violet right down to the most penetrating X-rays, which have a wave length 500 limes 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 investgators from searching the Unknown. The ultra-violet of the mercury uc produces a kind of snow-blindness, which, however, soon wears off. But it has an extraordinarily diversified effect on different substances. In uranium glass t produces a rich apple-green 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 Wil liain Crookes once started a brilliant assembly at the Royal Society by offering to test diamonds then and thereby means of ultra-violet rays, relying upon the fact, that none but a real diamond shows ’he characteristic phosphorescence. Even butter and margarine can be distinguished by their different appearance in ultraviolet light. The deciphering of the original-writing of a palimpsest by photography was a nuicn admired feat of the early eighties. This was, however, done by synply excluding all but the violet rays from the egative. The great flood o ultraviolet 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 exhibi tion 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 fugi live vegetation on the moon and Hale nas found the extraordinary mantle of vilcium cloudlets which covers the sun. Mr Baird reveals—somewhat unkindly, perhaps—how people appear when under infra-red illumination. The invention if a “ machine with a moral sense ” is i chimera, hut the best way of stamping out shams is lo make their detection easy and inevitable.