35-1 C. Bams — Large and Small Coronas. 



positive ions. Thereafter, case 3, the first is repeated, etc. 

 But if the coronas are taken as a measure of the number of 

 particles, the number of effective nuclei must be about eight 

 times larger in the first case than in the second, whereas the 

 1 2.3 4 



(+)—(-) (+)—-(-) 



H (+) H (+) 



I i I I 



ions should be present in equal numbers. Hence there is 

 serious objection to this hypothesis at the outset, quite apart 

 from the numbers obtained, which are enormously too large. 



11. Tinder saturation. — Some mechanism of this kind is 

 nevertheless probable, and it will work equally well if the 

 undersatu ration produced by the precipitation of fog particles 

 is not rapidly made up by diffusion and convection. Of all 

 hypotheses that of undersaturation has the broadest bearing 

 and accounts qualitatively for most of the phenomena, as will 

 presently be pointed out in detail. True, the large coronas 

 must be supposed to carry down more moisture than the small 

 coronas, but the difference need not be great. The hypothesis 

 encounters a serious obstacle inasmuch as the coronas obtained 

 from saturated air which has been imprisoned for long inter- 

 vals of time (§ 8), are usually an extremely small type of infe- 

 rior corona, whereas they should be large superior coronas. 

 Long intervals of waiting between exhaustions brings out not 

 a superior corona but at best one of intermediate size. 

 Another precarious feature is suggested by computating the 

 rate at which saturation should be established in the most 

 unfavorable case of the middle air layer, between the wet top 

 and bottom of the fog chamber, for diffusion alone. 



In fact if diffusion takes place from the wet top and bottom 

 of the rectangular trough of height a, into a partially saturated 

 atmosphere of initial vapor pressure p , then at any time t, at 

 the middle plate x = a/2 



p=l+ 4 fo-D /sin f «-(*/«)»* + I sin 3 5 € -(3V«)^ + etc \ 

 7r y 2 3 2 / 



where d/pfdb = k (d*p/dx 2 ). Hence if a = \l Qm as in the 

 largest trough (wood), and if h — *23, the following values 

 obtain. 



p = 1 /S, p = '52 j\ = 2/3, p = '76 



•72 -86 



•91 -96 



•97 -99 



30 



2>o=°> P = 



•28 



60 





•59 



120 





•87 



180 





•96 



