1879.] 



On Electrical Insulation in High Vacua. 



347 



The glass then gave way, and all the phenomena disappeared except 

 the extreme ends of the cross, and the discharge through the hole, 

 where the glass had been perforated, was alone seen. 



The phenomena were seen by Mr. Cottrell, by Mr. Valter (the 

 second assistant), and by myself. A fresh glass plate was at once 

 drilled in hopes of repeating the phenomena in the lecture next day, 

 but owing to sparks springing round we did not succeed in perforating 

 the glass, and therefore saw only the faint return of light described 

 by Dr. Kerr. 



Some more glasses have been prepared and their terminals in- 

 sulated, and I now propose to make another attempt to repeat the new 

 effects before the Royal Society. 



c 



February 20, 1879. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. "On Electrical Insulation in High Vacua." By William 

 Crookes, F.R.S. Received February 6, 1879. 



The experiments here described were tried nearly two years ago. 

 They were suggested by some observations I was then making on the 

 passage of an induction current through highly exhausted tubes. The 

 main branch of the research being likely to occupy my attention for 

 some time, I may be unable to return to these less important off- 

 shoots. I have ventured, therefore, to embody them in a short note 

 for the " Proceedings of the Royal Society." 



A pair of gold leaves were mounted, as for an electroscope, in a 

 bulb blown from English lead glass tubing. The leaves were attached 

 to a glass stem and the lower part of the bulb was drawn out for 

 sealing to a Sprengel pump as shown at fig. 1. A stick of ebonite 

 excited by friction was generally used as the source of electricity, but 

 any other source will do equally well, provided it is not too powerful. 



~No special attention was paid to the action of electricity on the 

 leaves in air or at moderate vacua, as it agreed with what is already 

 well known. The exhaustion was pushed to a very high degree (about 

 the millionth of an atmosphere), when it was found that the excited 



