X-RAYS AND THE ARTS.

Otago Witness, Issue 3418, 19 September 1919, Page 59

X-RAYS AND THE ARTS.

By Major G. W. C Kaye, M.A., D.S.C. The war has brought the X-rays into prominence on account of the incalculable service they have rendered to surgery and medicine. X-rays (which are invisible, and travel in straight lines) differ from light rays only in the fact that their wave-length is several thousand times shorter. This minuteness gives them the uncanny property of penetrating all classes of substances, whether optically transparent or not. The ease of penetration depends both on the thickness and on the density (or relative weight) of the substance, so that if an object is placed in the path of the rays a shadow picture will be cast on ap hotographic plate suitably placed. We can thus spy out the interior of an opaque body without opening it up. During the last year or so the method has been applied, more especially by the metallurgist and engineer, to the examination of all kinds of materials. The rays have, for example, been used to test whether there is flaw or crack in a metal weld. The steel manufacturer has radiographed his castings and forgingsin order that he might diagnose and localise blowholes and other imperfections to which they are prone. The aeroplane inspector has turned the rays to account in searching for any hidden faults either in workmanship or in the superfine quality of timber used to build the aeroplanes in which we have established so marked a 1 lead. The electrical engineer has employed the method to examine the quality of the carbon poles which lead the current in and out of electrical steel furnaces; or again, to scrutinise the carbon brushes for dynamos. The manufacturer of explosives has, by the same means, tested the correctness of the internal fittings of shells, torpedoes, cartridges, fuses, and grenades after assembly. The motor manufacturer has, by the use of the rays, photographed the interior of a carburettor while in operation, and so detected an illusive fault; in another instance a magneto was similarly scrutinised, and the cause of its imperfect working revealed. The method would also be very convenient for detecting hidden corrosion in metals —for example, in gas-cylinders or the armouring of cables. The rays have been used by the post office for testing the amount of mineral matter in guttapercha. At the moment the method is restricted by the limit to the thickness of material which can conveniently be penetrated. About ' two inches of steel is the present practical limit of the exfiosures are not to be intolerably long. n the ease of timber or the light aluminium alloys, now so largely used for the framework of rigid airships and many other purposes, the. above figures may be considerably exceeded. The niethod is very sensitive . fi> minute differences hi thickness—for example, the tool-marks used to face specimens are often clearly shown in radiographs of metals. Outstanding developments of what may bo called radio-materialography will probably only follow marked and necessary improvements in X-ray equipment, almost every part of which is .susceptible at present of much higher efficiency. In any event, however, we may anticipate novel outcomes as the possibilities of X-ray examination unfold themselves to users of material for constructional purposes. For instance, the combination of X-rays and the kinema- would permit the examination of hidden moving machinery. There is one other and entirely different way in which X-rays may supplement tht above method of examining material. Professor W. H. Bragg, F.R.S., to whom the subject owes so much, lias shown that the X-rays enable us to examine in detail the nature and extent of the crystallisation of a body. Now it appears to be the case that there is little in nature which is not crystalline to a, greater or less degree; arid, further, it is certain that crystalline structure is of first importance in determining the quality of substances such as steel. There is here a large field for the research worker.