column and other phenomena connected with the discharge. 305 



of potassium iodide. The gas was finally passed through potassium 

 permanganate and strong sulphuric acid before passing into the 

 apparatus. 



The nitrogen was prepared by heating a mixture of potassium 

 nitrate and ammonium chloride and passing the evolved gas 

 through strong solution of KHO and finally strong H 2 S0 4 . 



When a fresh gas was to be worked with the apparatus was 

 pumped down to a very small fraction of a mm. and refilled with 

 the required gas. This was repeated five or six times. 



It was found in working that when a tube had been running 

 for some time impurities made their appearance, as shown by a 

 direct vision spectroscope, necessitating the admission of fresh 

 gas. This was no doubt owing to gas being given off from the 

 electrodes. To get rid of this as far as possible it was found 

 necessary each time the gas was admitted and pumped out to 

 send a strong current through the tube at a low pressure for 

 some hours. 



Oxygen frequently allowed a large current to pass without 

 showing any luminosity save at the electrodes. 



It should be mentioned that in order to prevent injury to the 

 battery and also to provide a means of varying the current an 

 adjustable high resistance was placed in the circuit. This con- 

 sisted of two fairly wide capillary tubes having platinum wires 

 fused into their lower ends and nearly filled with water in which 

 a small quantity of salt had been dissolved. A platinum wire 

 bent twice at right angles connected the two at top and dipped 

 into the liquid, and the resistance could be varied by raising or 

 lowering this wire. 



4. Before giving details of the results of the measurements 

 made an account is given of the appearance presented by the 

 discharge under different conditions, in the hope that some, at 

 least, of the phenomena observed may be new. 



A remarkable appearance is frequently presented when a tube 

 freshly made is sealed on to the pump and the pressure reduced 

 to about '75 mm., the gas in it being moist air from the room and 

 not in communication with the drying bulbs. For example, in a 

 tube of about 12 mm. diameter which had been in use some time, 

 the striae were about 7 mm. apart when the pressure was "8 mm. 

 the gas being dry air, but when two fresh aluminium wire elec- 

 trodes were put in and the tube filled with moist air at the same 

 pressure as previously then they were separated by a distance of 

 1 mm. only, were much flatter than before and hair-like in ap- 

 pearance; the dark spaces between were also much more distinctly 

 marked. 



To what circumstances the production of these fine striae was 



