78 



VAPOR NUCLEI AND IONS. 



Table 26. Persistent nuclei produced after different lapses of time. Method, depres- 

 sion of asymptote, dp =26.4 cm.; Z?=io cm. above side of cylindrical glass fog 

 chamber; cock 1 J inches; exhaustion during exposure. 



1 Tempestuous fog and rain, leaving smaller corona. Second exhaustion made for safety, showing 

 small corona. 



. a 



400 



300 



BOO 



100 



zo 



40 



60 



80 



100 



ISO 



Fig. 36. Depression of efficient nucleation (n) of dust-free air ionized by strong X-rays 

 at a given exhaustion, by accumulation of persistent nuclei in the lapse of time- 

 Table 26. 



56. Water nuclei produced by evaporation. A beautiful method of 

 demonstrating the production of water nuclei in connection with the 

 condensation of fog consists in leaving the cock for influx of air from 

 the filter slightly open. In such a case the fog begins to evaporate as 

 soon as produced, and there will be less loss from subsidence of fog 

 particles, in proportion as the evaporation is more rapid; in other words, 

 as the stopcock is more widely opened. Table 27 shows results of this 

 kind and they are reproduced in fig. 37, where the abscissas are dis- 

 tributive. In every case the efficient nucleation (n) of dust-free air, 

 after complete subsidence of the preceding fog, is much in excess of 

 n', the nucleation observed when the fog is dispelled by evaporation. 

 The table also proves that the degree to which the filter cock (fine screw 

 valve) is open does not influence the result. 



