Lenard Rays, Discharging Power, Great Variety and Magnetic Deflection in Hydrogen

BY EDWARD P. THOMPSON.

The contents of a communication from Dr. Philip Lenard, of Heidelberg, may be of interest as shedding some light on the relations between X-rays and external cathode rays. The occasion of the open letter is my treatment of the external radiations from a discharge tube (Crookes tube), and especially my discussion of his own researches, which were originally published in several foreign proceedings of societies, and in foreign languages, some of them being published by Berlin Akad., January 15, 1893; Wied. Ann., January, 1894, LVI, p. 225; Wied. Ann., vol. LI, p. 259, and papers and articles of 1895 and 1896.

Translations of these and other papers, discussions of Lenard's results by other investigators and Lenard's latest theories were considered in my own language, under about 20 headings, in the book, "Roentgen Rays and Phenomena of the Anode and Cathode," setting forth in a classified manner the various facts, principles and theories relating to external cathode (or Lenard) rays.

Dr. Lenard, in stating that "we agree in all you have said on my experiments in the text of your book", discloses succinctly his present valued opinions on three points in this English letter. One of his remarks seems to indicate that he does not agree in all points with Professor Roentgen.

In Section 77, I stated:

"A remarkable occurrence was the accomplishment of the discharge at a much greater distance than that at which phosphorescence was exhibited. See also experiments of Roentgen, who suggested that Lenard had to do with X-rays in his experiment, but thought they were cathode rays. The maximum distance for the discharge was 30 centimetres, measured normally to the aluminum window. He (Lenard) admitted that the experiment was not carried far enough to know whether the effect was due to the action of the cathode rays upon the surrounding air or upon the plate."

The above related experiments were performed, it should be remembered, before Roentgen's discoveries.

Dr. Lenard now says, as stated in the letter referred to:

"I do not think the electric (discharging) actions at a great distance from the window of my apparatus due to Roentgen rays, because I have convinced myself in the meantime that these latter rays are only present in minute traces, and that there is another explanation of the effect observed. The air is made conducting by the deflectible cathode rays near the window, and afterwards extends to parts further apart, whilst retaining its conducting property."

As to the next point, I went so far in the matter of the variety of rays as to head one paragraph "Cathode Rays of Various Kinds are Variably Diffused." As intimated in his early papers, Lenard still reasons in the present open letter that there are "rays of an unbroken series of an infinitely great number of different rays, varying gradually in properties".

Lenard has generally been misunderstood regarding the magnetic deflection of cathode rays outside of the discharge tube. Dr. Lenard makes this point very clear. The book states, on page 66:

"The author could not find in Lenard's papers any positive or negative proofs that he had actually deflected the external cathode rays by a magnet while passing through air or gas at ordinary pressures.* * * * " Dr. Lodge, who briefly reviewed Lenard's experiments, expressed the same opinion. (See The Electrician, London, January 31, 1096, p. 439.) Dr. Lenard modifies this by saying, "I have effected the deflection in hydrogen. The deflection is not visible in air of ordinary pressure, only because such air is too turbid to show any distinct rays at all which could be distinctly observed at sufficient length to show deflectibility.”

Regarding the book in general, he very graciously condescends to compliment and encourage an American author by saying, "I find it very useful for getting information as to the very extended recent, literature on the subject;" and he exhibits the usual great man's modesty by referring to his world-wide known and wonderful discoveries, thus: "You have given much space to my own little share in the work."