120 



A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



20. Explanation of discrepancies. The reason for this result would at 

 first sight be obviously given by the evaporation of the fog particles on the 

 plate, before and during the photographic exposure. But as the d-values were 

 from 1.5 to 2 times too large, it is necessary to guard against accepting this 

 explanation too hastily: for inasmuch as the d-values and the w-values are in- 

 dependently given by the photograph, their relation must be 



nd 3 = 6m/n. 



Now it is rather curious that while the w-values are 4.5 times too small, the in- 

 dependent ^'-values should be 3 to 6 times too large. In other words, on 

 using the average d- and the average w-values given by the photographs, an 

 approximately correct value for m, the precipitation per cub. centim., follows, 

 even though d and n are found quite independently. Add to this the fact that 

 if evaporation occurs the photograph usually fails entirely. It is quite im- 

 probable that on the average a definite number, about 78 per cent., of the fog 

 particles should incidentally evaporate. 



Before proceeding further it will contribute to clearness if some of the 

 better data of table 4 be summarized. The d-values show the marked occurrence 

 of larger particles on the photograph, whereas the smallest particles more nearly 

 correspond in size. 



TABLE 8. SUMMARY OF CERTAIN DATA FROM TABLE 4. 



If the micrometer data (4-6) be used for the d-values, the ratios of 

 coronal and measured diameters are 



Ratio = 



4 



1.3 to 

 1.6 



6 



1.2 



1.6 



8 



1.2 



IO 

 1.2 



12 

 1.2 

 1-3 



or the d 3 -values are 1.7 to 4.1 times too large. Now in these instances the fog 

 particles were often measured while floating, so that adhesion in these instances 

 must have been a negligible factor. Nevertheless the d-values are not all in- 

 compatible with the w-values. 



