380 Mr Horton, The emission of positive rays 



and Reicheiibeim. The discharge tube was a round-bottomed 

 flask of some oOO — 1000 c.c. capacity. It was connected to a 

 mercury pump and McLeod gauge, and had a charcoal tube 

 attached for producing a low vacuum by means of liquid air. 

 Owing to the high melting points of the salts used in these 

 experiments, the tube A, which contained the anode, was of 

 fused quartz, 2 mm. internal and o mm. external diameter. The 

 aluminium phosphate to be used as anode was tinely powdered 

 and mixed with a little powdered graphite to render it conduct- 

 ing, and also with a little silver chloride to bind the mass together 

 when heated. This mixture was rammed into the end A of the 

 quartz tube to a length of 2 — 3 cms. The tube was then strongly 

 heated in a blow-pipe flame. This caused the silver chloride to 

 melt, and on cooling the mixture was tirmly held in the tube. 

 Electrical connection with this mixture was made by means of a 

 copper wire introduced into the tube at the other end and pushed 

 into the mixture while that was still hot. The cathode is the 

 aluminium ring K at the end of an aluminium wire, the straight 

 part of which is covered by a glass tube as shown in the diagram. 

 These tubes, from the anode and cathode, pass through holes in an 

 ebonite bung which closes the mouth of the flask, the joints being- 

 made aii'-ticrht with sealing-wax. 



The discharge through the tube was sent from a large Marconi 

 induction coil. It would have been better to have used a large 

 Wimshurst machine (following the method of Gehrcke and Reichen- 

 heim), but there was not one available. A spark-gap and a valve 

 of Lodge's pattern were usually placed in the secondary circuit of 

 the coil in order to prevent, as far as possible, the current from 

 passing in both directions. 



Perhaps it may be of interest to mention here that for obtain- 

 ing quickly the low vacuum required in these experiments, it was 

 found to be of great advantage to have the tube containing the 

 charcoal for cooling in liquid air made of fused quartz. During 

 the preliminar}' pumping a blow-pipe flame was played directly on 

 to the quartz tube, and in this way the charcoal was more quickly 

 and more completely freed from occluded gas. 



When the induction coil discharge passed through this tube 

 (the gas pressure being so low that no luminous gas was seen in 

 the bulb) the " torch " of light at the anode, described by Gehrcke 

 and Reichenheim, was obtained. On examination, the spectrum 

 of this light was found to contain the brightest silver lines, but no 

 lines of aluminium could be detected. In a magnetic fleld part 

 of the luminosity was deflected in the direction which would mean 

 that the rays consisted of positively charged particles leaving the 

 anode, and partly in the opposite direction, but I could never be 

 quite sure that this was not due to the discharge from the coil 



