280 



Mr. Norman Campbell on Delta Hays 



with aluminium foil connected to the base plate electrically. 

 B can be maintained at any desired potential by a battery of 



Fig. 2. 



WM^l _—_ ^A^^lAim 



£arth.<t 





L__ 





r 



.0 



j 



E/V/vi 



■SWA 



i 



1 



>: 



■QQvottsA 



Battery. 



-> electroscope. 



cells in combination with a potentiometer subdividing one 

 of them. For the purpose of this paper the E.M.F. of a lead 

 accumulator has been taken as 2 volts. 



The brass cover E, cemented to the base plate with a wax 

 composed of rosin and beeswax, enclosed the entire apparatus. 

 A high vacuum was established first with a Gaede pump and 

 then with charcoal and liquid air, which was connected to 

 the vessel throughout the observations by a tube not shown 

 in the drawing. As previous observers have noted, the 

 extreme vacuum obtainable by this method was not absolutely 

 necessary, but the usa of the charcoal rendered unnecessary 

 any attention to very small leaks. A rise in the pressure of 

 the gas in the vessel could always be detected by an increase 

 in the current that passed between the electrodes when a 

 magnetic field was applied to prevent the emission of delta 

 rays, 



