414 H. V. Gill — Electric Discharge in Geissler Tubes. 



lycopodium powder. This tube was 30 cm long. One terminal 

 being at the extremity, the other was situated 10 cm from the 

 other end. The tube was thus constructed in order to ascer- 

 tain if the mechanical effects to which we attributed the strati- 

 fication took place not only between the terminals but also, as 

 our theory demands, in the space which is not between them. 

 This tube was connected as shown in fig. 7, L being a large 



Leyden jar, A and B the discharging terminals of the Yoss 

 machine. By placing A and B at a suitable distance apart 

 sparks took place simultaneously at C and through the tube. 

 When A and B were l mm or so apart frequent sparks took 

 place, the space in the tube being stratified ; but these sparks 

 being very feeble, the powder, which had been arranged in a 

 continuous line throughout the whole length of the tube, was 

 not seen to be affected. We see at once from this experiment 

 that the spark in the Geissler tube is oscillatory, for evidently, 

 since the tube and the spark gap are in the same circuit, the 

 nature of the spark is the same at both points : but it has the 

 characteristics of an oscillatory discharge in the gap, therefore 

 it is oscillatory in the tube also. We confirmed this by placing 

 a card covered with lycopodium powder at a spark gap in the 

 circuit, including a Geissler tube showing stratification. The 

 powder was affected as in the experiments already described. 

 Now A and B were l-5 cm apart: at intervals of 10 or 20 sec- 

 onds intense sparks took place between A and B, the discharge 

 in the tube being exceedingly brilliant. After perhaps a dozen 

 such sparks the powder was definitely arranged. As the sensi- 

 tive paper was necessarily outside the tube the photographic 

 record was very indistinct, but the heaps in the tube were seen 

 to be exceedingly well defined. As some of the powder 

 adhered to the tube the heaps were not well defined in the 

 photograph, which is not reproduced here. 



Here it was noticed that the heaps of powder took place, not 

 only between the terminals, but also outside the line of dis- 



