1907.] 



BARUS— NUCLEI IN DUST-FREE WET AIR. 



77 



The best method of discriminating between water nuclei was found 

 to be the successive evaporation of fog particles precipitated on 

 the same nuclei under identical exhaustions, until the nuclei are 

 wholly removed by the exhaustion and subsidence. The results 

 may be exhibited in graphs, in which for about the same number of 

 initial nuclei, the persistence of the corresponding water nuclei is 

 shown by the number of nuclei which survive after successive evapo- 

 rations, in case of phosphorus nuclei, vapor nuclei and ions. Com- 

 pare figures 6 and 7. 



In case of phosphorus nuclei, after j: identical exhaustions, the 

 number of nuclei 71,^ remaining is given by 



where n^ is the initial number of nuclei per cubic centimeter, y the 

 exhaustion ratio and the product, IT, the correction for subsidence ; 

 but if ions or vapor nuclei are used, an additional coefficient of loss 

 x must be allotted to each exhaustion, so that 



The following example shows this clearly. 



Table I. 



The exhaustion loss, ,r, is thus greater in the second exhaustion, 

 or after the first evaporation of fog particles, three fourths to four 

 fifths of the number of fog particles precipitated on ions vanishing, 

 while one half to three quarters of the number of fog particles pre- 

 cipitated upon vapor nuclei vanish in the first evaporation, accord- 

 ing as the initial number is smaller or greater. The exhaustion loss 

 X is also greater for the case of precipitation on ions, as compared 

 with the precipitation on water nuclei. 



