72. CATHODE RAYS PROPAGATED, BUT NOT GENERATED IN A HIGH VACUUM.—The proposition was proved by having two tubes, one called the generating tube and one the observation tube, the former being like that shown in Fig. A, at beginning of chapter, which is partly repeated in Fig. F, at beginning of chapter, combined with the observation tube, which contains the two electrodes for casual use; but the one on the right is a disk extending nearly throughout the cross sectional area, and having a small central opening. Although both tubes were connected to the air pump, yet, by means of stop-cocks, the vacuum in one tube could be maintained at a maximum degree for hours, while the other was at a minimum. The first experiment was performed with a vacuum, about as high as that employed in Crookes’ phosphorescent experiments, § 53. There was a patch of green light, § 57, at the extreme left end of the observation tube and the glass was green at the right, § 54, and a little to the left of the perforated disk electrode _a_. The other electrode of this tube was located at the upper left and lettered _k_. 72_a_. The magnet deflected the rays _in the observing tube_ as indicated by the partial extinction of the phosphorescent patch. He noticed that with the rarefied atmosphere the amount of turbidity was enormously reduced, or in other words, that the rays were propagated more nearly in rectilinear lines. All the experiments on the cathode rays, in this observing tube, were of about the same nature as those which could be produced in the discharge tube. [Illustration: FROM SCIAGRAPH OF CAT’S LEG, BY PROF. WILLIAM F. MAGIE. Copyright, 1896, by William Beverly Harison, pub. of X-ray pictures, 59 Fifth Ave., New York City. ]