INCREASING SUPERSATURATION. 



vacuum chamber. It is noteworthy that very large coronas are then 

 met with on first exhaustion, a result which may bear on the expla- 

 nation of periodicity. 



In table 17 (figs. 24, 25) the goniometer was moved close to the 

 fog chamber to insure clearer vision. The chart (figs. 20-25) on 

 page 26 shows, , the number of nuclei per cubic centimeter of the 

 expanded air; in the tables the number, N, reduced to air at normal 

 pressure and temperature is usually given. 



TABLE 17.- 



-Cyclic variation of pressure difference. Cylindrical fog chamber, 

 valve. Eye at goniometer, 50 cm. from axis of cylinder. 



Plug 



* Nuclei probably enter from large influx of air through filter. Therefore next 

 coronas are small from undersaturation and periodicity. These fine nuclei get 

 gradually out of reach as dp decreases. 



21. Remarks on the tables. It will conduce to clearness to take 

 the last tables showing the increase of apertures, s, with the increase 

 of presure difference, 8/>, first in order. All the ^-curves, figures 20-25, 

 either pass through a maximum or reach an asymptote. If the 

 exhaustion is insufficient the groups of smaller nuclei will escape 

 precipitation and the coronas be relatively small. This will also 

 occur if relatively large nuclei are accidentally present. After all 

 nuclei, large and small, are caught, higher sudden exhaustion can no 

 longer increase the apertures. More water is instantaneously precipi- 

 tated per cubic centimeter. Nevertheless this counter-effect, if it is 

 such, will also vanish with increasing pressure differences, because of 

 the accentuated rapidity of thermal radiation. The adiabatic method 



