of view of the Kinetic Theory of Matter. 39 



cathode, the tube shown in fig. 13 was made. It consists of a 

 cylindrical tube 3*5 cm internal diameter, and 25 cm long. The walls 

 of the tube for about 8 cm in front of the cathode are flattened, 

 so as to be elliptical in form. The cathode is a spherical 

 aluminum electrode 2'2 cm diameter, and 2*5 cm radius of curva- 

 ture. The anode is a plane platinum disk, placed at right 

 angles to the axis of the tube, and 9 cm from the cathode. 



The form of the discharge stream from the cathode is shown 

 in the figure. When viewed from the direction of the longer 

 axis . of the elliptically-shaped walls, the discharge stream 

 appears as a narrow ribbon, the edges being almost parallel ; 

 from a position in the direction of the shorter axis of the ellip- 

 tically-shaped walls, the stream appears to cover the cathode 

 almost to its edges. From the surface of the cathode the 

 stream converges to a region of minimum thickness, and then 

 diverges until it strikes the anode. 



The modification of form of discharge streams, resulting 

 from the unequal velocity of the return streams from the glass 

 walls of the tube, may be further illustrated by the tube shown 

 in fig. 14. This is a cylindrical tube 3*7 cm internal diameter, 

 and 16 cm long. The aluminum cathode is cylindrical in form, 

 the radius of curvature being l*2 cm . The dimensions of the 

 electrode are : length parallel to the axis of the cylindrical sur- 

 face, 2*3 cm ; across the concave opening, 24 c,n . The anode is a 

 plane platinum plate set at an angle to the axis of the tube. 



The return stream from the walls of the tube (traveling in 

 straight lines) must leave the walls at a greater distance from 

 the cathode, in order to reach the central portion of the cylin- 

 drical surface, by coming over the sides, than by entering the 

 cathode from the ends. The electrification of the walls of the 

 tube falling off very rapidly from the cathode, the velocity of 

 those parts of the return stream which spring from points on 

 the walls of the tube near the cathode, must be very different 

 from the velocity of those parts coming from points remote from 

 the cathode. The cross-section of the discharge stream from a 

 cylindrical cathode ought, then, to be found to diminish more 

 rapidly (with decreasing molecular density), parallel to the axis 

 of the cylinder, than along the arc of the curved surface. 



At its first appearance the discharge stream from the cylin- 

 drical electrode seems to spring from the whole concave sur- 

 face ; but as the pressure in the tube is decreased, the stream 

 very soon grows narrow, as viewed from the side of the 

 cathode. The stream also grows smaller along an arc of the 

 curved surface ; but its rate of decrease with pressure along 

 the arc is at all times less than in a direction parallel to the 

 axis. As the stream vanishes, it still covers a considerable 

 length of the arc, while its dimension parallel to the axis is a 

 mere line. 



