232 



SCIENCE. 



[N. S. Vol. III. No. 59. 



investigators who extended very much what 

 Faraday had only commenced. Among the 

 numerous, most interesting, and indeed re- 

 mai'kable, results obtained by these inves- 

 tigators, the behavior of the discharge, 

 which under certain conditions, emanates 

 from the negative electrode, the so-called 

 cathode, was always considered as the most 

 remarkable. 



Fig. I. represents a typical form of the 

 vacuum tube capable of showing a strongly 

 developed cathode discharge. At a we have 

 one electrode and at h the other. They 

 consist of platinum discs attached to plati- 

 num wires which are sealed in the glass. 

 Let the electrode a be connected to the 

 negative, h to the positive pole of the in- 

 duction coil A. As the air pressure in the 

 tube is reduced, the color and the general 

 appearance of the discharge continually 

 changes character. When the pressure 

 reaches a small fraction of a millimeter of 

 mercury the intensity of the discharge in 

 the gas itself becomes very much reduced, 

 but in its place appears a strong fluorescence 

 of the glass. This fluoi-escence is produced 

 by faint streamers which proceed in straight 

 lines from the negative electrode, as indi- 

 cated by the straight lines in Fig. I., from 

 the disc at a toward the terminal c of the 

 tube. These streamers are called the ca- 

 thode rays. Professor Crookes, of London, 

 advanced the theory that the streamers rep- 

 resent a fourth state of matter, which he 

 called radiant matter. According to this 



theory there is matter moving from the 

 negative electrode, where it is projected by 

 the action of electric force, and whenever 

 this moving matter strikes the glass it causes 

 it to fluoresce. A radiometer interposed 

 properly in the path of the streamers will 

 be set into rotation. The fact that the 

 fluorescing portions of the tube become 

 very hot when the action of the coil is 

 powerful seemed to support Crookes' hy- 

 pothesis, namely, that there is along the 

 path of the cathode rays projected matter 

 moving with very high velocity. 



Other theories concerning these rays were 

 proposed, but none of them are entirely 

 free from serious objections. Ecintgen's 

 discovery will probably enable us to decide 

 very soon which among the several ex- 

 isting theories is the correct one. The 

 theory which probably has the most fol- 

 lowers on the continent will be mentioned 

 presently. 



Cathode rays are deflected by magnetic 

 force; the direction of the deflection is 

 roughly stated the same as if each ray were 

 a flexible conductor carrying a current with 

 one of its terminals attached to the cathode. 

 The late Professor H. Hertz discovered in 

 1891 that cathode rays are capable of passing 

 through thin sheets of metal like gold leaf, 

 aluminum, silver, etc., if these sheets are 

 placed within the vacuum in the path of 

 the rays. Dr. Lenard, an adjunct to Hertz, 

 extended this discovery two j^ears ago by 

 showing that the cathode rays can be made 

 to pass out of the vacuum tube into the ex- 

 ternal space, if the tube is provided with a 

 small window of thin aluminum. But as 

 soon as they pass into the external atmos- 

 phere they are rapidly absorbed ; this ab- 

 sorption results in a flourescence of the gas. 

 Various gases possess various degrees of 

 this absorptive power and the absorption 

 in a given layer of gas is propoi'tional to its 

 density. Solid bodies absorb them very 

 much more strongly on account of the 



