24 



case of a set of parallel tubes of small diameter as used bv 

 Townsend in his experiment upon the diffusion of ions. 



Comparing these results with those of fig. 6, it is seen 

 that, taking for comparison the brass gauze of 40 meshes per 

 inch, each wire, *007 in. diameter, and the brass gauze of 

 20 meshes per inch, each wire 010 in. diameter ; although 

 their discharging powers are as 5*45 to r65, nevertheless 

 with a field of 700 volts per cm., applied to their upper sur- 

 faces, exactly the same number of ions are drawn through 

 each. Again, twice the number of ions are drawn through 

 the parallel wire gauze having 24 strands to the inch, as 

 through the similar wire gauze having 40 strands per inch — 

 when a field of about 1,060 volts to the cm. is applied in 

 each case — although their discharging powers are respectively 

 175 and 12. 



§2. 



Returning to the result shown in fig. 5. It has so far 

 been assumed that the effects observed were due solely to the 

 intensity and distribution of the field around the wires of the 

 middle electrode. A question, however, suggests itself as to 

 whether the whole, or only part, of the diminution in cur- 

 rent which is observed when the fields on either side of the 

 middle gauze are in the same direction is due to the with- 

 drawal of ions from the lower chamber; for when the two 

 fields are opposed in direction no ions cross the top chamber, 

 while when the fields are in the same direction, some appa- 

 rently do cross it. 



It seemed conceivable that there still might be something 

 akin to partially combined sets of ions which, although un- 

 affected by the weaker field of the lower chamber, produced 

 ionization in the top chamber under the influence, not merely 

 of an intense field, but as the result of ions moving in an 

 intense field, through clusters such as have been already sug- 

 gested. This would also explain the lack of saturation shown 

 in the curves of fig. 6. 



An experiment was performed in an independent appa- 

 ratus. Two ionization chambers, provided with aluminium 

 windows, through which Rontgen rays could pass, were bal- 

 anced electrically against each other. Through the one was 

 drawn air which had been just previously subjected to the 

 influence of either radium or uranium, the ionization having 

 been subsequently removed by a weak field ; through the other 

 chamber a supply of air was drawn at the same speed. No 

 alteration in the balance could be observed. 



Again, a ring of copper- wire was made active by exposure 

 to thorium emanation, and placed on the upper surface of the 



