X-RAYSAND THEIR USES

Southland Times, Issue 23675, 25 November 1938, Page 15

X-RAYSAND THEIR USES

HISTORY OUTLINED BY DR ANDERSON ADDRESS TO ROYAL SOCIETY MEMBERS An outline of the accomplishments of the Roentgen ray since its discovery in 1895 down to the present day was given in a lecture on X-ray by Dr C. C. Anderson, M. 8., Ch.B., F.8.A.R., D. to members of the Southland branch of the Royal Society of New Zealand last evening. “Most of us are aware of the fact that the X-ray was discovered and so named by Professor Roentgen on November 3, 1895, but we are not aware that this was the culminating point of a number of hitherto unexplained phenomena, which had been puzzling scientists in various parts of the world,” said Dr Anderson. Sir William Crookes, an eminent English scientist, probably had as much to. do with the development of the X-ray as anyone, he declared. His name was associated with the tube with which the discovery was made and for many years the X-ray tubes were known as Crookes tubes. In 1872 he constructed a tube showing the heating effect of the cathode stream, a stream of electrically. charged particles of gas conducting the electricity across the partially evacuated tube. Those tubes must have produced enormous numbers of X-rays. On one occasion in 1879 such a tube produced so many X-rays that it damaged a packet of plates held in the hand of a laboratory assistant who was taking too much interest in the phenomena demonstrated. About' that time, unknown to the experimental physicist Helmholtz, a mathematician in Bonn, extended the provisions of a law promulgated by Clerk Maxwell, and not only foretolq that certain radiations would be discovered, but even foretold their properties. At this time the only electromagnetic radiations known _to the scientific world were the infra-red rays of heat, visible light and ultraviolet radiation. Helmholtz prophesied that there were other rays of much greater wave-length than the heat radiation, and that they would be found to have the property of passing through matter. These prophesies-were buried in the proceedings of some obscure philosophical society, and did not see the light of day for years, but he did stimulate an assistant named Hertz to demonstrate -wireless waves, -which subsequently bore his name —Hertzian waves. INVISIBLE RADIATION Roentgen had spent much time investigating the phenomena of the discharge tube, as the Crookes tube was also known, and had decided that the time had come to investigate these various phenomena which kept on appearing. His first step was to investigate the question cf invisible radiation emitted from the tube. This subject was not altogether an unknown quantity as people already were aware of the presence of ultra-violet radiation and its property of causing . certain crystals to fluoresce or glow in the dark. His investigations therefore were carried out in a darkened room with the tube so covered with black paper that no visible radiation was emitted. On the important day when all was ready he closed the. doors and shutters, put out the lights and switched on the machine. Lying on the table a yard or so away from the tube was a piece of cardboard covered with crystals or barium platinocyanide, which was known to fluoresce in ultra-violet rays. Immediately the screen glowed eerily. The scientist tested the . source of the rays by placing his hand between the tube and the screen, and the shadow of his hand appeared on the screen. He traced back the radiation to its source and discovered that, it was actually emitted from the walls of the tube. From that it was a short step to discover whether radiation affected a photographic plate, and then to discover the different degrees of penetrability of different substances. • “When he made known his discovery to a marvelling world he called these rays X-rays because their nature and many of their properties were unknown, but in most parts of the world they are now known as Roentgen rays in honour of their actual discoverer,” said Dr Anderson. One of the first reactions to the new photography was to apply it to all sorts of problems, he said. Enthusiastic zoologists, botanists and photographers as well as medical men all tried it out. It was an extraordinary fact that radiographs taken even in the early days bear favourable comparison with those taken at the present day. THREE GREAT BRANCHES The modern field of X-ray work could be divided up into three great branches, said Dr Anderson. First there was the medical branch which embraced diagnostic therapeutic subdivisions, and included veterinary work and even sylviculture; second, industrial, and third, research. A fourth, detection, might even be added, for X-ray had been called into use in society’s war against the forger and the smuggler. In the field of medical X-ray as a result of human ingenuity they were now able to examine with the X-ray every part of the human body. In addition to being employed so widely in the examination of the body, X-ray also was used in the treatment of numerous conditions and diseases.

The industrial branch of X-ray work already covered a wide field and almost daily was extending its borders. In 1897 M. Radiquet placed before the French Academy the results of some interesting experiments made by him in the examination of metals and the detection of internal flaws. For example, blisters could be seen in an aluminium bar one inch and a-half thick. In the last two decades much metallurgical investigation had been carried out. “Beside opening up possibilities of great savings to the manufacturer, metallurgical radiography also has a great effect in sociological economy,” said Dr Anderson. “Radiographic control of castings and other parts used in airships and other modes of transport has the effect of preventing the employment of unsatisfactory and weak components, and so in no small manner leads to' the reduction of fatal accidents.”

For many years pictures had provided a fruitful source of X-ray investigation, he said. In that way it was discovered that many of the old masters had been retouched or restored by later artists and that some had even used the complete canvas for their own confection without even bothering to remove the original work. The use of X-rays to detect smuggling was first employed by the French customs in 1903. The latest use, he believed, was for the detection of gems and other goods smuggled in bales. One glimpse with the X-ray could save hours of labour in unpacking and repacking suspected bales and it also obviated the necessity for a “hit or miss” method of examination.

A -number of lantern slides showing the effect of X-ray photography were shown by Dr Anderson, who was warmly thanked for his interesting and instructive lecture.