NUCLEATION UNDER VARYING CONDITIONS. 27 



22. Blurred coronas. The occurrence of an abundance of rain with 

 all the coronas, as well as the blurred appearance of the coronas them- 

 selves, shows that gradation of particles is a characteristic feature with 

 all these condensations. The following results for periodicity appar- 

 ently indicate the presence of a group of markedly large particles in 

 the amount of about one-eighth or more of the total number of nuclei. 



23. Time effect. In the lapse of time exceeding even half an hour 

 the aperture of all coronas usually diminishes in marked degree. Above 

 the fog limit, however, the coronas do not vanish as the result of 

 repeated exhaustion, i. e., the air can not be freed from nuclei by 

 being stored in a closed vessel (fig. 19). What is particularly remark- 

 able is the rapidity with which nuclei precipitated by condensation 

 are again replaced. Whether these come through the filter in quasi- 

 gaseous form (remembering that they must be much smaller than ions), 

 or whether they are spontaneously produced in the imprisoned air, is 

 yet to be decided. In every case something has to be explained away. 

 If the nuclei came through the filter, for instance, they would not 

 come through periodically. 



24. Oscillations at variable pressure differences. With increasing 

 pressure differences, 8/>, the superior and the inferior apertures each 

 lie on distinct curves, both of which rise rapidly at first, are then 

 rapidly retarded, and tend to reach distinct maxima (figs. 20-25). 

 The limiting ratio of apertures is liable to be nearly one-half. If, 

 however, the pressure difference is carried far enough, both ^-curves 

 sometimes change character by decreasing and increasing, respectively, 

 eventually to reach a common value. If, then, pressure difference 

 is in turn reduced from these final values, the oscillation of s is usually 

 absent and a mean nucleation appears at all subsequent (decreasing) 

 pressure differences. 



25. Nucleations at varying pressure differences. The increase of 

 nucleation, n, with the pressure difference, 8p, is difficult to interpret, 

 since the inferior and superior values are so much more widely and 

 irregularly distributed (figs. 21, 23, 25). The w-curves usually show 

 two limiting rates of increase of n with Sp, respectively very large and 

 very small. This is particularly well brought out in the data of table 

 1 6 and figure 23, where both loci are nearly straight even above 

 S/> = 4P cm. They become more so if the nucleation is reduced to 

 normal pressure, as shown under N. Using this suggestion the data 

 of table 13 (wooden fog chamber) are largely referable to inferior 

 coronas. With one exception, this is also the case in table 14 for the 



