DISTANCE EFFECT. 



II 



was shown elsewhere that below the fog limit of air, the nucleation 

 observed and due purely to radium at different distances, D, is, for 

 example (dp = 22), 



D 



N x io -3 . 



o 

 120 



10 

 50 



30 



32 



50 

 20 



100 

 12 etc., 



agreeing in character as far as may be expected with the data here in 

 question. These data multiplied by 4 (in other words \n X io -3 ) 

 are also given in fig. 6 for comparison. Hence the ions caught at dp = 

 41.5 are about four times more numerous than at dp = 22, and corre- 

 spondingly smaller. They behave, therefore, as if they were markedly 

 graded, but nevertheless, as a group, throughout much smaller than 

 the nuclei of dust-free air so long as the radiant field is appreciable. 

 While the number of nuclei continually grows smaller, with dimin- 

 ishing D, the efficient nuclei may nevertheless increase again below a 

 certain D, seeing that the colloidal nuclei in dust-free air are enor- 

 mously in excess, only a few of which are caught even in the absence of 

 radium. 



Table 5. Distance effect of radium. D measured from side. 



35 cm. 



>GBP. 



2 gyog'. 



3 wog. 



4 wrg. 



It would be more difficult to account for the result that the same 

 nucleation is observed wherever the radium touches the outside of the 

 elongated fog chamber. In other words, radium at the end of the chamber 

 in the earlier experiments seemed to produce the same mean nucleation 

 as when at the top, although the distances from the center of mass of 

 the glass are as 3 to 1 ; but the above experiments have already sug- 

 gested that this result was probably an incidental case. 



