Cathode and Lenard Rays. 231 



Fig. 2. 



of its base. This hole is covered with a piece of oiled silk fixed on 

 with sealing-wax, and the brass cup is then fastened on also with 

 sealing-wax to the tube. Oiled silk was used for the window because 

 with it no trouble is experienced in getting a piece thin enough, and 

 at the same time free from holes. It easily bears an atmosphere 

 pressure on an aperture 1 mm. in radius. 



The brass cup is connected to earth and used as the anode ; C is 

 the cathode. A is an additional terminal which may be used as the 

 anode. The cylinders a and b are arranged as in the last experiment. 



When the openings are directed towards e, and not more than a 

 few centimetres from it, the electrometer shows a negative deflection 

 which slowly rises to a value at which it remains constant. 



The cylinder b, with electrometer and connexions, had a capacity 

 of about 250 C.Gr.S. units, and in one experiment was raised to a 

 potential of 11 volts. The cylinder is not charged if, by means of a 

 magnet, the cathode rays are thrown off the window e ; neither is it 

 charged if the cylinders are tilted a little so as not to point directly 

 to e. The experiment was tried with a similar brass end of equal 

 thickness (1*5 mm.), but with no window in it, and no charge was 

 obtained. 



The negatively charged rays given off from the window are soon 

 stopped by the air at atmospheric pressure, and no effect is obtained 

 when the cylinder is more than a few centimetres from the window. 

 The experiment confirms that described above. The negative dis- 

 charge from the window may be shown in another way. 



A plate of ebonite is placed opposite the window at a centimetre or 

 two from it, and the coil turned on for a few seconds. The plate is 

 then dusted evenly over with a mixture of sulphur and minium, and 

 tapped lightly to clear it of the powder which does not adhere to it. 

 The well-known negative Lichtenberg figure is produced on the plate 

 with its centre at the point opposite the window. 



In Lenard's experiments he placed a screen of aluminium between 



