290 Prof. Richardson and Lieut. Bazzoni on the 



vertically and horizontally almost up to the rims of the coils,, 

 so that small displacements of the cylinder out of the centre 

 can have no influence on the results obtained when the ap- 

 paratus is in use. Since the discharge-cylinder was contained 

 within the coils, it was found necessary to compensate the field 

 inside the cylinder in order to prevent a shifting of the dis- 

 charge when the magnetic field was altered. This was done 

 by winding around the cylinder a two-layered solenoid the 

 dimensions of which were calculated to give a zero resultant 

 field inside for all values of the main field. Tests with the 

 fluxmeter showed this condition to be exactly attained and 

 also that no disturbances of the main field outside the sole- 

 noid resulted at distances greater than *2 or *3 cm. from its 

 walls. The connexions o£ the main coil and this compensating 

 solenoid were so arranged that the proper adjustment between 

 them was obtainable at all times by a single setting of the 

 series resistances. This circuit was taken from a 100 volt 

 main and carried up to six amperes. 



The apparatus was supported on asbestos props, so that 

 (after the magnetizing coils had been withdrawn) it could 

 be maintained at a bright red heat with a blowpipe flame or 

 otherwise as long as might be thought desirable. In the 

 preliminary treatments the whole of the quartz excepting 

 the seals was repeatedly maintained at a bright red heat for 

 half-hour periods, while a liquid air and charcoal vacuum 

 existed inside. In this way and by repeated electronic 

 bombardments of the electrodes under potentials up to 

 800 volts and currents up -to 30 milliamperes, the metal 

 parts were finally entirely freed from gas, at any rate as 

 far as the temperature ranges used in the experiments are 

 concerned. This end was, however, not easily accomplished. 

 Various extraordinary and in some cases interesting results 

 were obtained during tests made on the electrodes before they 

 were completely gas free. It was observed that as long as 

 any part of the apparatus was immersed in liquid air any 

 hydrogen which may be present is very rapidly eliminated 

 by the action of the glowing filament and thrown down in 

 an apparently modified state on the cold glass *. The 

 arrangement was entirely airtight, and after suitable heat 

 treatment held the highest vacua for indefinite periods. 



Running out vertically below the copper cylinder was a 

 quartz tube closed at the bottom which could be immersed in 

 liquid air. Just beyond M, which was expanded at the end 

 so as to receive within it a long glass cone and sealed round 

 with a small quantity of hard wax, was a glass liquid 

 * Cf. Langmuir, Trans. Amer. Chem. Soc. vol. xxxiv. p. 1310 (1912). 



