196 Mr Rudge, Experiments on the Retention, etc. 



or separately by two pumps. To use the apparatus, one of 

 the electrodes A or B was put in connection with the earth, 

 and the other presented to the Wimshurst. If the pressure 

 was below 1 cm., then, on bringing a wire connected with A 

 near to B, a bright spark passed, and both chambers were filled 

 with a glow. " Residual " charges could be obtained as with 

 an ordinary condenser. After the condenser has been charged, 

 the air may be removed from it, fresh air admitted, then re- 

 exhausted, repeating this time after time, discharging by earthing 

 the knob after each exhaustion, and still some slight charge will 

 be left. An endeavour was made to ascertain whether the air 

 itself inside the flash was charged, so with this object, the air on 

 the way from the flash to the pump was made to pass through an 

 insulated metal tube (which was sometimes packed with iron 

 filings) connected to an electroscope, but no signs of electrification 

 resulted. Exploring electrodes were also inserted in the con- 

 denser, without any definite result. The next essay was to find 

 out whether the air removed from the flask during exhaustion 

 possessed any conducting power, and for this purpose, it was 

 drawn through a glass tube containing two conductors separated 

 a short distance, one being in connection with a charged electro- 

 scope, the other in connection with the earth. Only a very slight 

 leak of the charge from the electroscope was observed, so that the 

 air had not become appreciably conducting, or rather, those por- 

 tions removed did not possess conducting power. Experiments 

 were undertaken with gases other than air, viz. hydrogen, oxygen, 

 carbon-dioxide, carbon-monoxide, and sulphur-dioxide, when it was 

 seen that with the exception of hydrogen, the behaviour of the 

 gases was similar to that of air. Hydrogen acted somewhat dif- 

 ferently from the rest, for the charge would not remain as long as 

 with the other gases. 



Another set of experiments was conducted in a somewhat 

 different manner. After placing the unexhausted condenser in 

 connection with the Wimshurst, a wire was used to connect per- 

 manently the knob and the tinfoil, and then the apparatus was 

 exhausted. When the pressure fell to about 8 — 10 cm. a faint 

 glow was seen to fill the bulb, and as the pressure was further 

 reduced, occasional bright flashes were observed. The glowing 

 effects lasted for quite a long time (several minutes), and if air 

 were admitted to destroy the glow, it reappeared after reex- 

 haustion, without any further charge being given to the apparatus. 

 A curious effect followed the use of hydrogen, viz. it was diffi- 

 cult to get the apparatus to work with air afterwards. Until, 

 in fact, all traces of hydrogen had been removed by repeated 

 exhaustions and fillings with air, the glow discharge could not be 

 obtained. 



