57. CATHODE RAYS RECTILINEAR. RADIATE NORMALLY FROM THE SURFACE OF THE CATHODE. In his lecture he had, side by side, two bulbs, one, in which the vacuum was of such a degree, that a blue stream of light existed between the negative pole and positive pole, § 54, at centre. It is evident that the vacuum in this bulb was not very high. Fig. 9, p. 17, shows a stream extending from the negative to the positive pole, Fig. 10, p. 17, is the same kind of a tube only the vacuum is about 1 to 2 m. In other words, the vacuum in the latter was just so high that a discharge took place, and instead of the luminous effect being like that with a low vacuum, there was a patch of green light directly opposite the concave negative pole. The radiations from this pole were rectilinear, crossing each other at a focus within the bulb and producing upon the glass a phosphorescent spot. It should be remembered that the word radiations is used as a mere matter of convenience. Directly opposite the concave cathode, there was a green patch of light on the inner surface of the glass. It was shown that it made no difference where the anode was. This fact becomes useful in carrying on experiments in connection with Roentgen rays, and it may have a great deal to do with the solution of the theoretical problems in connection with electrical discharges in vacuum tubes. In regard to the three streams shown in Fig. 9, p. 17, it may be stated that only one occurred at a time in the experiment, for, first one anode was connected in circuit, and then the next by itself, and then the third one by itself, while the concave pole was always negative. Each time the anode was changed, the stream changed, and connected that pole which was in circuit, § 43, but similar changes made upon the tube with a high vacuum, did not alter the position of the phosphorescent spot. This and other experiments show that the radiations took place perpendicularly from the surface of the cathode.