Röntgen Ray Experiments

Abstract

IT has been generally noticed that when focus tubes become much blackened, presumably by volatilisation and deposition upon the glass of the platinum of the anode, they cease to be effective owing to the apparent increase in their internal resistance. This is generally attributed to increase in the vacuum due to the occlusion of the residual gas by the platinum black. This may in part be the true explanation, but another is to be found in a curious phenomenon discovered by Prof. Crookes, and described in his 1891 presidential address to the Institution of Electrical Engineers. He says: “It appears that the greater the phosphorescing power of the substance surrounding the poles, so much easier does the induction spark pass. Surround the poles with Bohemian glass or Yttria—two phosphorescent non-conductors of electricity—and the induction spark passes easily: immediately I surround the terminals with a non-phosphorescent conductor” [a film of deposited silver] “the current refuses to pass.” Very possibly the deposited platinum in an old or overworked focus tube has a similar effect to the silver in Prof. Crookes' experiment. I have recently had experience with a tube of special form which was much blackened, and which appeared to have an enormous internal resistance, though its blue appearance and other indications pointed to rather a low vacuum, which seems to show that this is the case.