1896.] 



25 



that pass in a rectilinear direction from the negative electrode, or 

 cathode, of a suitably exhausted vacuum tube. This peculiar eft'ect is 

 not observed to any marked degree until the residual atmosphere in the 

 tube has a tension or pressure of but about the one-millionth of an 

 atmosphere, or until that peculiar condition of matter in the tube is ob- 

 tained, for which Crookes proposed the name of the ultra-gaseous, or 

 radiant state. It appears that wherever (he cathode rays strike the 

 walls of the tube, or any suitable substance contained therein, they 

 excite fluorescence. The cathode rays are deflected by magnetic flux. 

 Indeed, they must be so deflected if they consist of streams of electri- 

 fied molecules ; for, their deflection by magnetic flux is a phenomenon 

 allied to the deflection of a voltaic arc by a magnet, or the deflection 

 of the active wires on an electromagnetic motor, by the flux from the 

 field magnets. 



Reviewing briefly the history of the Rontgen discovery, we will find 

 some of the facts to be as follows; viz., Hertz showed that thin metallic 

 films are transparent to the cathode rays. Lenard, an assistant of 

 Hertz, who afterwards took up the investigation both in connection 

 with Hertz and individually, placed an aluminum window in the tube 

 so that the cathode rays impinged on it. You probably noticed, in 

 looking at the radiation from the tube shown by Prof. Goodspeed, that 

 the rays did not light up the entire surface of the tube, but that a spot 

 directly opposite the cathode was markedly excited by the phos- 

 phorescence. That is the spot where a peculiar kind of radiation, called 

 the Lenard rays, or the Roatgen rays, was observed ; the Lenard rays 

 in one condition of the vacuum, and the Rontgen rays in another con- 

 dition of the vacuum. Assuming, that the cause of the Lenard or 

 Roatgen rays is the impact of a molecular stream of electrified particles, 

 most iDrobably molecules, we may inquire as to their origin. They are 

 evidently either disengaged from the substance of the negative elec- 

 trode or cathode, or they are simply the molecules of residual gas in the 

 highly exhausted tube. Inasmuch as Pupin has shown that electrode- 

 less Crookes tubes, that is, tubes not provided Avith interior electrodes, 

 produce the same effect, it would seem fair to believe that botht he 

 Lenard and the Rontgen efi'ects may be due to molecular bombardment 

 of the molecules of the residual atmosphere. In these electrodeless 

 tubes, pieces of tinfoil are placed on the outside of the tube, and the 

 terminals of the Ruhmkorflf coil being attached to them, discharges are 

 produced by electrostatic induction corresponding to the discharges of 

 the secondary of the Ruhmkorff coil, and all the eff'ects of either the 

 Lenard or the Rontgen rays are produced. 



Lenard states that his rays are faintly visible to the eye outside the 

 tube. They are, however, rapidly absorbed by the air, so that at a 

 short distance from the tube they cease to be visible. The Roatgen 

 rays, on the contrary, are invisible to the eye. Both the Lenard and 

 the Rontgen rays produce phosphorescence in phosphorescent materials 



PROC. AMER. PHILOS. SOC. XXXV. 150. D. PRINTED MAY 25, 1896. 



