Chuniiini f/n'oin/h Jon Ahsorplion. 51)1) 



point itself no cliarge is giwrn n[). Tlio state of balance is, 

 liowever, not maintained, for the ratio of i)ositive to negative 

 ions rapidly increases owinor to the recombination of the 

 positive and negative ions to build neutral molecules. From 

 this point onwards more positive than negative ions reach the 

 wall — a positive charging of the remainder of the tube being 

 the result. Thus the negative charging found by Zeleny 

 and the positive one found by Villari are both due to the 

 same cause, viz. the greater rate of diffusion of the negative 

 ions. 



Having explnined these experiments by assuming different 

 coefficients of diffusion for the two kinds of ions, the question 

 arises — are we justified in assuming, as Townsend has done, 

 that positive and negative ions act as molecules of two 

 separate gases mixed with the ordinary unionized gas from 

 which they are formed, as such obeying Avogadro^s law, 

 and having different coefffcients of diffusion quite indepen- 

 dently of their electrical properties ? Although Townsend 

 has used this assumption in interpreting the results of his 

 experiments, the ions in those experiments were not free 

 from their electrical proj)erties, for Avhen an ion comes into 

 the neighbourhood of the solid wall of a tube, it induces there 

 an opposite charge, and under the influence of the field so 

 formed moves towards the wall. But Zeleny showed that in 

 a given field negative ions have a greater velocity than 

 positive ones ; hence the negative ions will move quicker 

 than the positive ones tow^ard the wall, so producing the 

 apparently different coefficients of diffusion. 



Thus we are not able to say, from Townsend's experiments, 

 that negative ions really have a greater coefficient of diffusion 

 than positive ones in the same sense that we say two gases 

 have different coefficients of diffusion. Realizing that the 

 only way to settle the point is to isolate a mass of ionized 

 air and then to investigate the rates of diffusion of the two 

 kinds of ions into the surrounding unionized air, an attempt 

 was made to find a method of doing this. Yortex rings gave 

 a simple means. A box from which vortex rings could be 

 sent out was placed albove a Rontgen tube so that the air 

 within could be strongly ionized— a lead covering prevented 

 the rays from ionizing the air in the room. On tapping the 

 elastic side of the box, when the Rontgen tube was in action, 

 a mass of ionized air was sent out into the unionized air of 

 the room. In order to investigate the effect of diffusion the 

 rings were directed into a gauze cage connected to an elec- 

 trometer and ]H'operly protected against outside electrical 

 fields. AVhen the cage was 20 cms. from the orifice from 



