1909] on Problems of Helhmi and Radium. 1^1 



cylinder, B, more than 3 ft. in height and 8 in. diameter, is mounted 

 an electric discharge-tube, C, stimulated from a transformer and 

 provided with steel, platinum, aluminium, or other electrodes, about 

 1 cm. diameter and 4 cm. long, the whole discharge tube being sur- 

 rounded by a water-jacket, D. An exhaust-pump, capable of dealing 

 with a large leak of gas, while still maintaining a pressure of from 

 1 to 5 mm. of mercury, is connected to the metal base, M, on which 

 the cylinder is mounted vacuum tight. This base is fitted with stop- 

 cocks, and connected to a mercury manometer, E, for controlling the 

 exhaust. The gases are admitted at the top, where they can be 

 regulated by the cock, F. 



For obtaining pure air, oxygen and nitrogen, these gases were 

 vaporized directly as required from the respective liquefied gases 

 through narrow lead pipes soldered to the top of brass tubes about 

 1 ft. long and 1 in. wide, covered over the ends with flannel to act 

 as a filter when dipped into the respective liquids contained in 

 vacuum vessels. The narrow lead pipes are connected to the inlet 

 screw-down regulating valves, CI, fixed to the table on which the 

 apparatus is set up, the common outlet tube, H, being connected by 

 another narrow lead pipe to the stop-cock F at the top of the glass 

 cylinder, passing through a small tubulated spherical bulb, K, into 

 which organic and other vapours are introduced by saturating a little 

 cotton wool rolled on the end of a wire with the respective organic 

 liquids. This combination affords a very effective and ready means 

 of obtaining large currents of gas in a state of purity, necessary to 

 ensure good phosphorescence in large scale experiments required for 

 lecture demonstration. 



The gas stream is thus seen to form a phosphorescent axial core. 

 The discharge-tube is mounted on a ball and socket union, a, 

 so that the gas stream can be deflected in the cylinder. A glass 

 cup, h, mounted immediately under the top plate of the cylinder, can 

 be turned under the orifice of the discharge-tube so that the enter- 

 ing gas stream impinges into it. The gas stream is thus broken up 

 into a luminous cloud overflowing the cup and filling the upper part 

 of the glass cylinder. A horizontal metal plate, c, can similarly be 

 moved into the stream ; this causes a general scattering of the 

 beam. When the air current is started, it rushes down the tube at 

 a velocity of about 1000 ft. a second, and a steady brilliant phos- 

 phorescent stream appears down the whole length of the cylinder. 

 On increasing the amount of the entering air, the stream is shortened 

 and assumes a brush-shaped formation. A thermo-junction, d, con- 

 nected to a reflecting galvanometer, indicates change of temperature 

 when the phosphorescent stream passes over it. Similarly the beam 

 can be deflected on to a small insulated metal sphere, e, con- 

 nected to a charged electrometer,/. When this is done, rapid dis- 

 charge of the electrometer shows the ionization of the gas particle 

 forming the phosphorescent stream ; even should phosphorescence be 

 YOL. XIX. (No. 103) 3 B 



