X-rays and localisation / by James Mackenzie Davidson.
- Davidson, James MacKenzie.
- Date:
- [1902]
Licence: In copyright
Credit: X-rays and localisation / by James Mackenzie Davidson. Source: Wellcome Collection.
Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)
5/12 (page 5)
![1902.] graphic plate. He then excited the tuhe by the electric current and then developed the photographic plate. He found the image of his strip of platinum, as he expected, but he also found a second strip which he could not explain. On examining the door he found that the unexpected strip came to be opposite the beading. It was a pine door, varnished but unpainted. At first he wondered whether the additional thickness of the beading would account for the unexpected strip, but he found wood so transparent, that this view was untenable. He then removed the beading from the door. The explanation was then obvious. Some white lead had been used to cement the strip to the door, and it was the white lead which by its density had caused the shadow on the photographic plate. It is remarkable that Professor Eontgen, in his original com- munication concerning the X-rays, described almost all the properties which they are known to possess. Very little, indeed, has been added during these seven years. The chief advance has been in the.methods of their application to surgical and medical work. I will now explain how the X-rays take origin in a Crookes' tube. This rough model illustrates the path of the cathodal stream by means of these cords. A curved cathode, similar in shape to an ordinary reflector, is made of aluminium. The cathode rays emerge from it normal to its surface and converge towards a point, then proceed for a short distance in a straight line, and then gradually diverge—wherever this cathodal stream impinges upon solid matter X-rays take their origin. From what has been previously said, it would naturally occur to you that X-rays must have been produced long before they were discovered. This is so. Looking backward, we now know that Crookes in his researches must have been producing X-rays from his tubes. Lenard, no doubt, had X-rays intermingled with the cathode rays which he had so laboriously got outside his tubes. In the early tubes which Eontgen used, the cathode stream was allowed to impinge upon the bottom of the glass tube. The con- sequence was that the X-rays took origin from a more or less large surface, and consequently the photographs produced by a tube of this kind were necessarily rather blurred; but Professor Jackson, of King's College, London, suggested putting in the interior of the tube a metal anode, inclined as you see in this modern tube, and in this way the converging cathode stream from the concave cathode impinged upon the platinum target, giving rise to X-rays richly from a com- paratively small point or surface. This model served to illustrate what happens. The slide now thrown upon the screen illustrates the importance of the proper distance of the anode from the cathode. It should be so placed as to meet the cathode stream at its narrowest part. The impact thus gives rise to a rich production of X-rays from a point, and sharp shadows on the fluorescent screen or photographic plate are thereby produced. A matter of some practical importance is that all parts of the tube which fluoresce green give off X-rays to some extent. And B 3](https://iiif.wellcomecollection.org/image/b21638858_0007.jp2/full/800%2C/0/default.jpg)
