The Guardian And Evening Star, with which is incorporated the West Coast Times. WEDNESDAY, JANUARY 5, 1927.

Hokitika Guardian, 5 January 1927, Page 2

The Guardian And Evening Star, with which is incorporated the West Coast Times. WEDNESDAY, JANUARY 5, 1927.

SEEING IX THE DARK. Thekb appeared recently ill one of our newspapers a short account of the discovery by Baiitl of an invisible ray which might he expected to do wonderful thing's. In the absence of a more reliable, scientific account of the 1 discovery one hesitates to prognosticate hut it is unfortunately characteristic of sensational journalism that emphasis is laid upon, possibilities related to the uses of war. Baird, as we know, has lieen carrying out some important researches in connection with wireless television. Sonic account of his work was recently given in. this column, when it was pointed out that his transmitter made use of ultra-violet light to modulate the carrier wave. It is probable that the new “ray” is simply a beam of ultra-violet light. The field of invisible light waves is a fascinating one for the scientific explorer, and many wonderful things have already been done in the way of using dark rays. Wireless itself, for example, might lie said to he essentially a method of communication by means of Invisible light waves. Ether waves may bo classified in much the same way as sound waves, viz., in octaves, but. whereas the ear is sensitive to several octaves of sound, the normal eye perceives only one octave of light. As there are about fifty-three octavos of ether waves known to science the limitations of direct vision will lie appreciated. In immediate proximity to the visible octave—or what we call) colour-—there are the ultra-violet rays on the one hand and the infra-red rays on the other. Both of these hands, though dark to the human eye, are fairly well known and can ho utilised for a number of purposes. It is well-known, for example, that ordinary photgraphv utilises the ultra violet. A photographic impression on a negative is largely the work of invisble light, which partially accounts for the fact that the tone values in a photograph of coloured objects differ so remarkably from the impression formed through direct vision. It may be news to some tliat it is possible to take photos in a room that appears to the eye to be absolutely dark. All that- is necessary is to use a source of “illumination” rich in ultra-violet rays, to enclose it in a screen of “chance” glass so as to allow only the ultraviolet rays to pass. It would he necessary also to substitute for the glass lens of the camera one made of quartz, sine ordinary gloss is fairly opaque to ultra-violet. Suitable sources of illumination would bo a carbon are, a tungsten arc, n mercury vapour lamp or a calcium flare. Astronomers make frequent use of the ultra-violet in photographing the stars, and. in particular, the sun. In this ease, however, the result is accomplished by setting the camera in different parts of the invisible spectrum. Infra-red photographs may also lie taken with special plates. Direct vision of an object illuminated by a beam of invisible light is of course impossible, but there are several indirect means of attaining the same object. Tt is possible, for example to change the wave length lengthening it or shortening it so that it comes ultimately in the region of the visible spectrum. This is the well-

known principle of fluorescence. If a strong beam of ultra-violet light- is caused to play upon an object, an Image of t-lie object may be thrown, bv means of a quartz lens, upon a fluorescent screen, and so rendered visible. Suitable fluorescent are willemite (silicate of zinc), barium platinocyanide, and uranium glass. A corresponding shift of infra-red rays into the visble spectrum is called ca-lore-seenee. For this purpose platinised platinum may ho used. During the war various applications of the above principles were utilised for secret signalling. A second and more complicated method, but one which extends the distance of vision enormously, lias been made possible by the recent researches in television. A travelling spot of ultra-violet light may be used to modulate a carrier wave. This is subsequently demodulated by a noon lamp and the image thrown on a screen. This method was recently described in the articles on television appearing in this column. It involves, as will be seen, an ultimate change of wave length to the visible spectrum. It will lie obvious that there is plenty of room for research in this field. Doubtless Baird’s new discovery, if indeed it is new, is a further and more effective application of the above principles. Let, 11s hope that it will be used for something better than a new weapon of war.