40 J. E. Moore — Electrical Discharge from the point, etc. 



The importance of the return stream from the walls of a 

 tube in determining, not only the form and cross-section of the 

 discharge stream, but also the region of the cathode from 

 which the discharge stream springs, is illustrated by the tube 

 shown in fig. 15. The tube is a simple glass cylinder, about 



15. 



24 cm long and 3'5 cm in diameter. It is provided with two 

 spherical aluminum electrodes, each of 2*5 cm radius of curva- 

 ture. The electrode (a) is 2'7 cm in diameter, while (b) is l'6 cm 

 in diameter. The electrode (a) is set eccentrically in the tube, 

 so that the edge opposite the point of support is nearly in con- 

 tact with the inner surface of the glass wall of the tube. The 

 electrode (b) is also set eccentrically, but in the opposite direc- 

 tion. 



When the pressure in the tube is low, and (a) is made 

 cathode, a small, well defined, discharge stream is seen to 

 spring, not from the center of the electrode, but from the 

 point of intersection of the axis of the tube and the electrode. 

 The stream, springing from the electrode normally to the sur- 

 face, makes an angle with the axis of the tube. As the walls 

 are cylindrical, the cross section of the discharge stream is 

 circular. 



Finally, it may be mentioned that it has been found that the 

 form of the discharge stream from a plane, convex, concave, 

 or ring cathode, at a pressure just higher than that at which 

 the stream vanishes, appears to an observer to be almost 

 independent of the form of the electrode. 



Princeton University, Princeton, N. J. 



