54 



Mi;. O. W. RICHARDSON ON THE IONISATTON 



atmospheric pressure per squ.-m- centimetre of surface per minute, not the slighest 

 change could be detected in the value of the negative leak. This proves indubitably 

 that the negative ionisation produced by hot platinum in air is not due to traces of 

 alorbed hydrogen. 



The apparatus used in this part of the investigation is shown in fig. 1C. The 



Fig. 16. 



platinum tube ABA' was about 15 centims. long, and its internal and external 

 diameters were 0'05 and O'lO centim. respectively. It was clamped at each end by 

 the metal supports E, E', and heated by means of a current let in at D, I)'. The 

 current of hydrogen or air inside the tube was let through by means of the glass 

 tubes A, A' sealed on at each end of the platinum tube. The temperature of the tube 

 was measured by means of the thermocouple C, C' of platinum and rhodioplatinum 

 welded on to the middle point B. The wire was surrounded by three aluminium 

 cylinders, F, G, and F', to the middle one of which the leak was measured. The 

 outer cylinders acted as guard rings and maintained a uniform field near the central 

 uniformly heated part of the tube B. The dimensions of the middle cylinder were : 

 length = 3 centims., diameter = 3'2 centims. The various supports E, I, 1', E', could 

 slide in holes cut in a slab of vulcanised fibre LL', which was used because ebonite was 

 found to buckle with the heat. When they had been adjusted in position they could 

 be clamped by means of screws. The vulcanised fibre was not found to be sufficiently 

 good insulating material, so the support L to the testing electrode was protected by 



