Gases by the Motion of Negatively charged Tons. 201 



connected to one terminal of a battery of lead cells, the other 

 terminal of which was connected to earth. The upper plate 

 B was connected by the -tube T to one pair of quadrants of an 

 electrometer, the other pair of quadrants and the case being- 

 connected to earth. The wire joining the tube T to the 

 quadrants passed along the centre of brass tubing which w r as 

 connected to earth, and thus formed a screen for the wire. 



Strips of tinfoil were gummed round the glass vessel C 

 both on the inside and the outside, and were kept at zero 

 potential bv means of earth connexions. The lower edges 

 of the bands were within 2 centimetres of the zinc plate, so 

 that no charge could leak from the plate A over the surface 

 of the glass and influence the potential of the upper plate and 

 the tube T. 



The ebonite legs supporting the apparatus rested on a box, 

 covered with lead, containing a Rontgen-ray focus-bulb, and a 

 Ruhmkorff coil. A circular hole was cut in the lead covering, 

 and the bulb was placed so that the platinum anode should 

 be vertically under the centre of the aperture. 



The direct rays traversed the space between the two plates, 

 above the aluminium window ; and the insulated disc B, 

 which was of thick brass, prevented the radiation from 

 penetrating into the upper part of the apparatus. At the 

 s-'ime time the brass plate gave out a secondary radiation 

 which increased considerably the ionization between the 

 plates. 



3. The experiments were conducted in the following manner. 

 The wire connecting the upper plate to the quadrants was 

 put to earth and the lower plate was raised to the required 

 potential ; the upper plate was then insulated. The deflexion 

 on the electrometer-scale, produced when the rays were acting 

 for 10 seconds, was observed. The electrometer showed no 

 leak until the bulb was excited ; and after the rays were 

 stopped, the electrometer reading remained perfectly steady, 

 showing that the current between the plates does not continue 

 after the rays have ceased to act. 



The connexion between current and electric force was 

 thus obtained for five different pressures, and the numbers 

 obtained are represented graphically by the accompanying 

 curves, figs. 2, 3, 4, 5, and 6. The current between the 

 plates varies slightly, in magnitude, on reversing the electro- 

 motive force. The mean of the two currents obtained by 

 reversing the electronic tive force is represented by the curves. 

 The difference in conductivity is generally small and could 

 have been avoided by using two aluminium plates; but the 

 advantage thus gained would not compensate for the loss 



Phil. Mag. S. 6. Vol. 1. No. 2. Feb. 1901. P 



