32 Prof. R. Threlfall on the Electrical 



Tube 6. — Dec. 5, 1891. This is the tube shown in fig. 2. 

 All drying apparatus exhausted twice ; tube prepared by 

 a steady discharge during December 11th; left till 14th to 

 test for leaks, when it was found that the whole apparatus 

 was air-tight. Tube again sparked hard all December 14th 

 with best pump-vacuum attainable. Electrodes at a bright 

 red heat for 1^ hours ; mercury separated by long tube and 

 boiled in pocket. Sealed off at about 6 millirn. pressure on 

 December 15th. 



Dec. 16. Sparked 2 hours through capillary water resist- 

 ance ; tube slightly warm. No effect. 



Dec. 17. Sparked so as to produce a yellow glow for 

 3 hours and by small blue sparks for 1 hour. No effect. 



Dec. 18. Sparked with fairly strong discharge for 8 hours. 

 Tube too warm to read : so left till December 3 J st, when it 

 was found that the tube pressure had diminished by *2 millim. 

 This led to an examination of the tube by holding a sheet of 

 white paper behind it ; and it was found that a bronze-coloured 

 film had formed where mercury had condensed near the top 

 of the capillary tube. The mercury within the sphere of action 

 was only the most minute trace. Sparked 3 hours and on. 



Dec. 22. Effect about *3 millim. Sparked for about an 

 hour, and then on careful examination it was found that the 

 glow was actually passing down the tube to the mercury. It 

 was clearly of no use to go on with the experiment in this 

 way, and consequently the mercury was boiled into the tube 

 and the spark turned on. The effect diminished during the 

 boiling from '35 millim. to '3 millim. Sparked then for 

 5 hours ; effect increased to 1*2 millim. 



Dec. 26. Sparked 4 hours. Effect 2*4 millim. 



Dec. 27. Ditto 3 hours. Effect 4*3 millim. 



Dec. 28. Sparked for one hour, when it was noticed that 

 the tube-resistance had increased and the gauge showed 5*38 

 millim. of effect ; hence the tube is nearly empty. On first 

 turning on the spark, the illumination began by being strong 

 for about one minute. The striae were well marked, and the 

 mercury spectrum prominent. After about one minute the 

 luminosity diminished to that corresponding to faint blue 

 sparks. In twenty minutes the tube was again hot and fairly 

 luminous, and continued with luminous sparks and rising tem- 

 perature for 35 minutes : the gauge showed that the rise of 

 temperature (?) was producing an increase of pressure. Tube 

 cooled for one hour, w T hen it was found that the excessive 

 sparking had at last cracked the tube near the platinum wire, 

 and that some mercury had been drawn in. The tube was 

 then cut into bits, and one was heated in a test-tube in a 



