of Crookes on the one hand, and Lenard and Roentgen’s discoveries on the other. Dr. Lodge, F.R.S., (_The Elect._, Lon., Jan. 31, ’96, p. 438,) and Lenard, in his first paper, attributed to Hittorf the discovery of the mere existence of cathode rays, but credited to Crookes the full establishment of their properties, deduction of their principles and formulation of an ingenious theory. 61_a_ As an appropriate conclusion to Crookes’ work, I cannot do better than to let Lord Kelvin repeat what he said in his Pres. Addr., _Ro. So._, Nov. ’93, see also _The Elect._, Lon. Feb. 14, ’96, p. 522, showing that a small portion of the credit is due not only to Hittorf, § 53, but to Varley. “His short paper of 1871, which, strange to say has lain almost or quite unperceived in the _Proceedings_ during the 22 years since its publication, contains an important first instalment of discovery in a new field, the molecular torrent § 53, at centre, from the ‘negative pole,’ the control of its course by a magnet, § 59, its pressure against either end of a pivoted vane of mica, § 59, at end, and the shadow produced by its interception by a mica screen, § 58. Quite independently of Varley, and not knowing what he had done, Crookes (_Roy. Inst. Proc._, April 4, ’79, vol. LX, p. 138. _Ro. So. Trans._, ’74, “On attractions and repulsions resulting from radiation” Part II, ’76, parts III and IV, ’76, part V, ’78, part VI, ’79) was led to the same primary discovery, not by accident and not merely by experimental skill and acuteness of observation.” * * * * “He brought all his work more and more into touch with the kinetic theory of gases; so much so, that when he discovered the molecular torrent he immediately gave it its true explanation—molecules of residual air, or gas or vapor projected at great velocities (probably, I believe not greater in any case than 2 or 3 kilometers per second, § 61_b_), by electric repulsion from the negative electrode. This explanation has been repeatedly and strenuously attacked by many other able investigators, but Crookes has defended (Presidential address to the _Inst. Elect. Eng._, 1891.) it, and thoroughly established it by what I believe is irrefragable evidence of experiment. Skillful investigations perseveringly continued brought out more and more wonderful and valuable results; the non-importance of the position of the positive electrode, § 57, near end, the projection of the torrent perpendicularly from the surface of the negative electrode, § 57, at end; its convergence into a focus and divergence thenceforward when the surface is slightly concave, § 47, near beginning; the slight but perceptible repulsion, § 60, between two parallel torrents due, according to Crookes, to negative electrifications of their constituent molecules; the change of the direction of the molecular torrent by a neighboring magnet, § 59. the tremendous heating effect of the torrent from a concave electrode when glass, metal or any ponderable substance