Mr. F. L. Woodward, of the Scientific School, has devised a new form of ray lamp, by means of which excellent radiographs have been obtained. As the sides of the lamp permit cathode rays to pass through them, the fact that with it radiographs may be obtained contradicts the theory that a glass envelope plays an essential part in the generation of Rontgen rays.
This new form of ray lamp is that of a cone, and its characteristic difference from the ordinary Crooke's tube is that the sides or walls of the lamp are made of sheet aluminum 1/10 in. thickness; the base of the lamp is made of solid glass, practically a plug fitted into the base of the aluminum cone with paster-of-Paris, and made air tight. A metallic ring passes around the base of the cone and holds the sides of the cone firmly to the glass bottom. Through a point a little to the side of the centre of the glass base, passes the cathode pole into the lamp, and at the end of this is fastened a platinum disc, at such an angle as to be parallel with the side of the lamp. At the top of the lamp and directly connected to the metallic side, is the anode pole, and at the top of the cone is a glass tube with a cock-stop, so that the air may be exhausted. This glass tube is also fastened in with plaster-of-Paris and bound by a metallic ring. A circular wooden disc is fastened in the inside of the metallic cone, to prevent any collapse of the sides on exhaustion. By this construction it has been found that the difficulty from the absorptive power of the rays by the glass of the Crooke's tube has been eliminated in a most marked degree.
As yet, Mr. Woodward has worked with this lamp with induced currents of from 25,000 to 30,000 volts, and with such very clearly defined radiographs of the hand have been taken in five seconds.
It seems from this that with more experimental work and a higher current, say, 50,0000 volts, that an instantaneous photograph may be taken, and the heavier parts of the body readily photographed.
The new form of ray lamp has an interest aside from its construction, from the fact that experiments conducted with it appear to disprove the theory that a glass vacuum envelope plays a significant part in the generation of Rontgen rays. This theory, which was advanced by Dr. Rontgen himself, has been strongly supported by Poincare and provisionally accepted by other authorities. Yet Mr. Woodward has obtained excellent shadowgraphs from the radiations passing through the sides of the aluminum cone of his lamp. This supports another theory that has been offered, to the effect that Rontgen and cathode rays are independently generated in a vacuum tube, but that the former alone have the power of traversing the glass envelope. The fact that clearly defined radiographs of the hand were taken in five seconds show that Rontgen vibrations are greatly weakened in passing through the glass of the ordinary vacuum tube; this, however, was to be expected in view of the opacity of glass to such rays, as indicated in radiographs.