tlie Residual Gaseous Matter in a Crookes Tube. 391 



the cathode-cup, and the aperture iu its containing glass bulb 

 faces the cathode so that the cathode-rays can impinge upon 

 the platinum. The other and shorter pole has its platinum 

 plate well to oue side of the cathode, and has the aperture in 

 its glass cup turned away from the cathode towards the anode. 



Fig. 2. 



Experiments were conducted with this tube highly exhausted 

 and excited by means of an induction-coil, the polarity of the 

 two exploring-poles being ascertained by means of a quadrant- 

 electrometer. With the aluminium cup as cathode and the 

 plate as anode, the longer exploring-pole, which has its bare 

 extremity facing the cathode-stream, was found invariably to 

 be charged negatively, while the other and shorter exploring- 

 pole was found always to be charged positively. This was 



