82 



VAPOR NUCLEI AND IONS. 



holding negative ions? Do they retain their charges, or some equiva- 

 lent of the charges? As there is less mobility and slower recombina- 

 tion in cases of ions entrapped by water nuclei, one would infer greater 

 opportunity for the gravitational separation of the equivalents of the 

 positive and negative charges; for it seems improbable that the water 

 nuclei resulting can be of the same size. 



Finally, in table 31 data have been gathered showing the gradual self- 

 purification of the fog chamber, after cleansing and sealing. Nuclei 

 arising from some internal source cease to appear in the mere lapse of 

 time and without further interference. The coronas s x and s 2 are observed 

 in successive exhaustions at the time (days and hours) given. Initially 

 the first corona is smaller in marked degree, owing to the spurious 

 nucleation within. After more than three days, however, both coronas 

 s x and s 2 are identical. 



Table 31. Purification of the fog chamber in the lapse of time. <J/> = 3i. 

 cock 2\ inches; piping 12 inches long, 2 inches in diameter. 



Exhaust 



1 Vacuum maintained some hours. 



' dp= 36. Internal source of nucleation absent. 



The source of this transient internal nucleation is difficult to detect. 

 There were no leaks. Oil evaporation if harmful would be continuous. 

 The same differences of fresh and stagnant air in relation to s t and s 2 

 are always reproduced. There is no evidence that anything in the 

 vacuum chamber is capable of diffusing into the fog chamber. Some 

 agency therefore, which is productive of relatively large nuclei, and the 

 nature of which is not clear, survives many consecutive precipitations. 



57. Distance effects. X=rays. In the following experiments I endeav- 

 ored to overhaul the curious results obtained when the X-rays strike 

 the fog chamber from different distances, without, however, reaching 

 very satisfactory conclusions. The object of the following work is to 

 bring to bear the newly improved means on the problem. In table 33 

 data are given as obtained with the glass fog chamber, the drop of 



