552 POPULAR LECTURES AND ADDRESSES. 



could be done in the way of exhausting (supposed 

 to be down to I mm. of mercury) by the best air- 

 pump of fifty years ago. A large part of the fresh 

 discoveries in this province has been made by 

 the authors of these communications ; and their 

 references to the discoveries of other workers very 

 nearly complete the history of all that has been 

 done in the way of investigating the transmission 

 of electricity through highly rarefied air and gases 

 since the time of Faraday. 



Varley's short paper of 1871, which, strange to 

 say, has lain almost or quite unperceived in the 

 Proceedings during the twenty-two years since its 

 publication, contains an important first instalment 

 of discovery in a new field the molecular torrent 

 from the " negative pole," the control of its course 

 by a magnet, its pressure against either end 

 of a pivoted vane of mica according as it is 

 directed by a magnet to one end or the other, and 

 the shadow produced by its interception by a mica 

 screen. Quite independently of Varley, and not 

 knowing what he had done, Crookes was led to the 

 same primary discovery, not by accident, and not 



