136 A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



As this is not a perfect differential I assumed the relation (jf v and 9 

 to be approximately that of air, v''~'B = const., supposing that I could subse- 

 quently correct for the precipitated water by successive approximation. In 

 this way one obtains at the beginning and the end of the exhaustion for any 

 two temperatures S and S' (using accents throughout for the latter case), after 

 integrating, x'/x = {B'/r'){r/3—lg{3'/B)), where {x~x')/x is the mass ratio of 

 precipitated liqtiid to the original vapor. In my work thus far ' the results 

 computed in this way and for 6p = ly cm. were at 10°, 20°, 30°, w X 10* = 

 .59, 1. 13, 1.85 grams, respectively, where the corrections for precipitated moist- 

 ure have been applied and dp is an isothermal value. If 6p, the observed 

 pressure reduction, were treated adiabatically the corresponding values of 

 m X loi would be .42, .76, 1.28. 



The restilts for m so obtained will have to be rejected as they are much 

 too small (probably because the pressure coefficients were overlooked) when 

 compared with the more direct approximation of Wilson and Thomson. The 

 value of in is here found as an intersection by making the m values compatible 

 with the vapor density curve for water. These data have already been com- 

 puted for the pressure difference Sp^ij above, table 2, and will be used in 

 Chapter IX. 



g. Relation of nucleation to aperture of corona. — A stunmary of the method 

 of deducing the nucleation (number of nuclei per cubic centimeter) from the 

 observed coronal aperture for an observed pressure difference {6p=i'j cm.), 

 in the given apparatus, has already been fully explained in Chapter VII, § 26, 

 and needs but Httle further reference here. 



Measurements of the aperture 5 would naturally be made as far as the 

 inside of the red ring or the circumference of the eventually white disc ; but in 

 such a case they bring out very strong periodicity in the first place, and are 

 soon subject to large errors due to the increasingly vague and washed outline 

 of the disc. Hence measiirement is more appropriately made to the dark blue 

 ring which limits the green coronas or to the dark interior of the green ring in 

 the crimson coronas. These lines are not only sharper bvit they reduce the 

 periodicit}'. It is understood that with air nuclei and 6p = 17, the green corona 

 is seldom exceeded. Otherwise it would be necessary to increase the tmiform 

 pressure difference, against which there is no objection other than the increased 

 practical inconvenience, provided the pressure difference for which saturated 

 air condenses spontaneously (above dp = 22 cm. in the above apparatvis) is not 

 exceeded. 



10. Absence of electrification in cases of sudden condensation and of sudden 

 evaporation. — It has long been known as the result of most painstaking observa- 

 tions, that neither in cases of ordinary evaporation nor of condensation is there 

 an accompaniment of electrification. On the other hand, when a mass of 

 water is suddenly shattered, as in jets, the electrification is marked, while it is 



^Smithsonian Contributions to Knowledge, No. 1373. 



