312 Pr, S. Guggenheimer on the Spark-discharge. 



Opposite these electrodes was an aluminium window over 

 which a brass cover could be placed. One end of the tube was 

 connected to a U-tube filled with calcium chloride and thence 

 to a wash-bottle containing concentrated sulphuric acid. 

 The other end of the tube was connected by means of a glass 

 tube (from 8 mm. to 2 cm. diameter and 10 cm. length) to a 

 second brass tube of 20 cm. length, and of the same diameter 



Fig. 1. 



H_ 



as the first one. This second tube was connected at the 

 other end by means of a U-tube containing calcium chloride 

 to a blowpipe. In the side of this brass tube was an opening 

 8 cm. long and 2 era. "broad, which was closed by thin 

 aluminium-foil. 



One part of the electric circuit comprised the one pole of a 

 Wimshurst machine, the inner coating of a leyden-jar, one 

 of the spherical electrodes, and the indicating portion of a 

 Eraun electrometer ; the other part of the circuit consisted 

 of the other pole of the Wimshurst, the outer coating of the 

 leyden-jar, the other sphere, and the cage of the electrometer, 

 and was generally put to earth. 



The observations were carried out in the following order: — 

 (1) The discharge-potential was measured without exposing 

 the sparking system to radiation, and without introducing 

 ions into the tube A. Then (2) from an X-ray bulb placed 

 near the aluminium window of the tube B, strong X-rays 

 entered B, and the ions thus produced were driven by a 

 strong current of air into the tube A, and the potential was 

 measured whilst this operation went on. (3) A third measure- 

 ment was then made whilst X-rays fell directly through the 

 aluminium window in A upon the electrodes. The current 

 of air was also blown through the apparatus during the 

 operations 1- and 3. Sheets of lead protected A when B was 

 exposed to radiation. 



I give below the results of two particularly striking series 

 of experiments. 



