152 Prof. J. Zeleny on the Ratio of the Velocities of the 



To determine this, one of the glass side-plates of the box 

 PQ (fig. 2) was replaced by an ebonite one, which had at its 

 middle an air-tight horizontally movable slide. This slide 

 carried the wire used for finding the potential of the different 

 points in the air-current between the plates. On the inside 

 end the wire had a loop which occupied a symmetrical position 

 in the air-stream, while the other end was connected to a pair 

 of quadrants of an electrometer. 



Two potentials for the plate Q were found (as in §4), 

 one positive and the other negative, which with a certain air- 

 blast produced in the same time the same numerical deflexion 

 of the electrometer connected to the gauze T. 



The gauze was now connected to earth, and the potential 

 gradients were determined separately while each of these two 

 actions was in progress. In doing this, both pairs of quad- 

 rants were at first connected to a battery-potential supposed 

 to be equal to that of the point in the apparatus which was 

 under investigation; and when the blast and rays had acted 

 a sufficient time for a steady state to be reached, the pair of 

 quadrants connected to the wire was insulated from the 



Fi<r. 15. 



battery, and any change now taking place in the electrometer 

 deflexion indicated whether the potential given to the wire 

 by the battery was larger or smaller than that of the point in 

 question. Potential gradients determined in this way with 

 air in the apparatus are shown in fig. 15. 



