462 PROCEEDINGS OF THE AMERICAN ACADEMY. 



denser of .02 m f capacity was charged to a difference of potential of 

 100.000 volts and discharged through the rarefied tube by flat copper 

 bands of inappreciable self-induction. The photographs showed un- 

 mistakable striae, superposed upon the general illumination of the 

 tube. It is difficult to reproduce the photographs by half tones. 



With an anode consisting of a ring of wire placed in a cylindrical 

 tube .5 mm. internal diameter, a striation is formed at a short distance 

 from the anode by condenser discharges, and there are traces of 

 similar striations at greater distances along the tube. If these stria- 

 tions are formed by ionization by collision, the time of ionization is 

 that of the duration of the pilot spark, a time which at present is 

 beyond our power of measurement. 



3. Doppler Effect. 



When two anodes and two cathodes are employed in the form of 

 tube represented in Figure 7, there are two canalstrahlen which ema- 

 nate from orifices in the cathodes in opposite directions. One might 

 suppose that the Doppler effect would be modified by collision of 

 the particles in these rays and that the effect would certainly be less 

 than when only one anode and one cathode were employed — the cur- 

 rent thus passing through but one branch of the U tube. It is true 

 that the difference of potential is less between A and D when the 

 tube is coupled in multiple circuit than when only one branch of the 

 tube is connected to the battery; but this difference in the case I 

 studied was comparatively small. With both branches of the tube 

 constituting a multiple circuit there were two strong canalstrahlen 

 passing through the orifices in D which were undistorted and which 

 gave the same Doppler effect which was obtained when only one 

 branch of tube was excited ; it seems difficult to reconcile this result 

 with any theory of collision. 



4. Conclusions. 



1. The striae in Geissler tubes are analogous to waves set up in 

 narrow channels by opposing pulsations of different periods. 



2. Striae are greatly influenced by the direction of cathode rays. 

 Certain forms of tubes, described in this article, can imitate the action 

 of a transverse magnetic field in apparently increasing the conducti- 

 bility of the rarefied gas and restoring the condition of stratification. 



3. Striae can be formed by condenser discharges; and such striae 

 lead one to suppose a time of ionization beyond our power of measure- 



