A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



137 



6 



CL 



1 



not obvious that the underlying cause is friction. The electrification soon 

 vanishes, however, whereas the nucleaticn persists. The question thus arises, 

 therefore, whether in ordinary slow evaporation the absence of an electrical 

 effect may not be due to the possibility of charges vanishing too quickly to be 

 noticeable. It seemed worth while, therefore, to examine the case for the 

 sudden condensation and the rapid evaporation of fog particles. 



To test this question a graduated electroscope was introduced into the 

 condensation chamber. To insulate it in the satu- 

 rated atmosphere, the stem was enclosed in a hard 

 rubber tube, as in figure 5, open below and only in 

 contact with the stem at the top by a sealing-wax 

 joint. The tube was thoroughly dried before in- \ 

 scrtion into the condensation chamber, and the 

 instrument showed satisfactory insulation for a 

 half -hour or more, after which it was removed for 

 desiccation prior to new experiments. 



Condensation was produced by exhaustion as 

 usual, and the nuclei used were obtained from air 

 as well as from phosphorus. The method of pro- 

 cedure consisted in observing the normal leakage 

 of the charged electroscope by observations made 

 every half -minute. Nuclei were then introduced 

 and the experiment repeated with the alternate 

 sudden production and sudden dissipation of fogs 

 between each observation. 



The two curves of leakage were not distinguish- 

 able, even when the fogs were of the densely opaque character due to phosphorus, 

 and the error of the method was about 5 per cent., with somewhat larger un- 

 certainty for the case of fog evaporation. 



Pressure differences, however, were kept below the limit (much above 

 dp = 22 cm. in the given apparatus) at which saturated air spontaneously con- 

 denses without nuclei. This phase of the question, which in fact is rather the 

 more interesting one, is thus left at issue. If, for instance, dust -free air is always 

 slightly ionized and thus contains unstable systems, the increase of ionization by 

 sudden exhaustion in virtue of the unstable molecules referred to is by no means 

 excluded. The question has been touched above. 



ii. Conclusion. In the above paragraphs I have endeavored to present 

 the complications to which the method of coronal registry of atmospheric 

 nucleation is incident, complications which were not anticipated and for which 

 I was altogether unprepared. In the course of my work I made several un- 

 fortunate blunders in endeavoring to reduce the data to absolute values, but 

 apart from these the greater number of discrepancies (as, for instance, the 

 periodic distribution of nucleation in terms of aperture) could not have been 

 foreseen at the outset. 



L 



FIGURE 5. APPARATUS TO DETECT 

 IONIZATION PRODUCED BY SUDDEN 

 CONDENSATION. 



