“BLACK LIGHT.”

Otago Daily Times, Issue 20353, 9 March 1928, Page 12

“BLACK LIGHT.”

TELEVISION METHODS. SEEING BY WIRELESS. JOHN BAIRD’S DISCOVERIES. Science has given to man the eyes of a super cat, so that lie can see in black darkness, and over a distance of hundreds of miles without any other connecting link than the tenuous ether. Last .September a journalist in London, sitting in a darkened room, saw another in Leeds —170 miles away. While conversing over the telephone,” the cable message said, ‘‘ he watched his lips foim tlie words, lie saw his colleague laugh, put out his tongue, and move the instrument of vision. The features and expression were very clear. Both were'in darkness, and the transmission was carried out in infra-red rays, which are claimed to have tlie same results as wireless. . . it is to the sou of a Scottish minister that th e world owes this latest invention. He is John Baird, the man of 37 years, who perfected television, making it possible for people to see at a distance by means of wireless. Now he has come Mong and made us a present of one of the com-monly-suppressed attributes of the feline tribe. Television in itself is a marvel. Last May people in London were enabled to see images of others in Glasgow— a distance of 438 miles, and it is hoped that before long television will be possible across the Atlantic. But the new invention—which has been named “ noctovision ” —goes a long way further than television, and promises to effect a revolution in certain phases of life in war, in the detection'of crime, in shipping, and in dozens of other directions. What is this artificial sight that pierces the dark ? It is really an invisible searchlight—it is “ black light,’ the application of a ray which, while itself invisible to the human eye, is able to penetrate further than ordinary lightBaird discovered that there was outside the human spectrum, a ray which he named “infra-red.” This is the ray that does the work. It can be thrown farther than visible light—literally, it puts the ordinary searchlight beam in the shade. In was in connection with his experiments last year with television that Baird discovered this new ray. For a person to be “ televised ” he had to be subjected to a light so powerul as to be almost burning and blinding. That made the apparatus commercially impossible, so after many experiments the inventor succeeded in reducing the light to normal. Then it dawned upon him that his apparatus was something whose electric “ eve ” was quite different from tha human eye. It was a question of relativity. Tlie rays which made vision possible to man might not apply to this machinery. Other rays, beyond the scope of our eyesight, might be used. ,He tried ultra-violet rays, but found them so powerful that they scorched the skin of the subjects of the experiments. He had to abandon them. Moreover, they had nob the requisite penetrative powers, being absorbed after they had passed through a thin layer of air. Ultra-violet rays are at one end of the spectrum. Baird decided to try with the other end, where he found the infrared. So successful were these that, na was able to dispense altogether w ith visible light. Later Baird was able to give public demonstrations of his discovery, and one of the first of these was before members of the Royal Institution. _ About c 0 members accepted the invitation to visit the laboratory in London, where the apparatus had been made, and in small groups of half-a-dozen at a time they went into the transmitting room, while others took their places in the receiving room. Though the transmitting room was “ lighted,” it was in complete darkness, as far as the human sight was concerned. Certain filtering devices which excluded from the light all but the infra-red rays were used. In the receiving room was a groundglass screen, and, to the amazement of the spectators, on this there appeared perfectly recognisable living images of the heads and shoulders of those near the transmitter in another room. The actual transmitting was done by means of the “ televisor,” but previously this instrument had been used only in “ visible light.” The early experiments were carried out at Baird’s laboratory. They were in complete darkness. On one occasion a well-known scientist went into the transmitting room, in company with a laboratory assistant, while another went into the receiving room, on another floor. In tliis latter room the image of the assistant’s head was shown brilliantly illuminated on the screen, and all his motions could be closely followed. The images, it is stated, were no mere shadowgraphs or outlines, but real images made bydiffused reflected rays. Television carried the pictures, hut the infra-red rays enabled television to work in darkness. Later, Baird lectured in St. Andrew’s Hall, ’Glasgow, where he gave miniature exhibitions of the use of the ray. Across the darkened hall to a table on the platform a beam of the infra-red rays was sent, and by their invisible agency -in turn a bell was rung, a lamp lighted, and a toy mine exploded. Following this, full-scale demonstrations were given, and the inventor has erected on the roof of his London laboratory a special apparatus. He has found that the ordinary searchlight is particularly rich in infra-red rays. He fitted cne with a light-filter which made it appear that the light had gone out, but in reality the only rays which were allowed to pass the filter were nonvisible infra-red rays. It is proposed by means of the seaichhght to pick out at night an aeroplane which will fly overhead. Tho vision of the aeroplane, of course, would be projected onto ’ the ground glass screen. The “ black-light,” as it has been called, will, when perfected, be of enormous value to shipping in fegs. Baird intends to have his apparatus mounted on a ship in order to carry out fog-penetration tests at sea. The experiments conducted between Leeds and London early in September were a definite vindication of the inventor's claim. They were mads at a time when the annual congress of the British Association was sitting at the former city, and the cable mentioned earlier in this article was the result of them. They were a complete success, the images of persons in Leeds being perfectly reproduced in London. And all this was done in pitch darkness.