30 Mr. J. J. E. Durack on Lenard Bays. 



to prevent the discharge taking place from the rod, and it 

 was also found necessary to cover the back of the disk with 

 glass (as shown in the diagram) when intense Lenard rays 

 were required. An aluminium cylinder a a was used as 

 anode. 



Tier. 1. 



The end o£ the discharge-tube facing the cathode was 

 drawn down and a brass tube t cemented on with sealing-wax 

 coated on the outside with a layer of (Munich) soft wax *. 

 An aperture about 1*5 mm. in diameter was bored in the end 

 of the brass tube, the brass being rather thick to prevent 

 heating, and the hole bevelled on the inside ; on the outside a 

 piece of aluminium-leaf, '0043 mm. thick, was fastened with 

 soft wax. This constituted the window W. 



A water-j acket j j surrounded the tube t to keep the window 

 cool and so prevent melting of the soft wax. The discharge- 

 tube was kept connected to a Topler pump and McLeod 

 gauge. 



An outside tube, which, following Lenard, I shall call the 

 observation-tube, was cemented on to the tube t with sealing- 

 wax; this tube contained the camera 6, was closed at the end 

 with a rubber stopper D, and connected to a Fleusspump and 

 manometer. 



The velocities were found by measuring the magnetic 



* Sealing-wax joints, if properly made, are absolutely air-tight, that is 

 to say I was unable to detect any leak in a discharge-tube with such 

 joints when the tube was left unused for three weeks, the pressure of air 

 in the tube during that time being less than *01 mm. To make these joints, 

 the parts to be joined should first be heated sufficiently to melt the 

 sealing-wax (as has been before pointed out by several experimenters), 

 the parts can then be pressed together while the wax is soft, and a uni- 

 form joint made by heating the wax till it flows smoothly, care being taken 

 not to burn the sealing-ivax : if the sealing-wax is burnt little bubbles 

 break on the surface and probably allow the air to leak in ; the soft wax 

 serves to cover up these holes if any are formed. 



