A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 43 



undulation continues even beyond this, but it is then diffictdt to identify it, as the 

 annuH become crowded into the normal coronas. The results are similar in all 

 the curves. In other data obtained during experiments with jets in Chapter II, 

 ^§4, 5, 17, and given in the present figures 6, 7, 11, 12, the same undulatory line 

 is encountered both for phosphorus and for water nuclei, with maxima at the 

 9th and 14th coronas. Here a different vessel (aspirator 32 cm. high, 22 cm. 

 in diameter) was used, and the ratio, 6d=i.:iSd', is distinctly smaller for this 

 case, showing the marked influence of distortion due to the vessel. The same 

 ratio (1.3) will be adduced below in connection with the preliminary experi- 

 ments with plate-glass apparatus. 



4. Nucleation. — Since nd^ is constant, remarks of the same general char- 

 acter may be made for the nucleation, n, except that the discrepanc}^ will be 

 reciprocal in character and enormously exaggeraterd. If on the average d=i.^d', 

 w' = 3.4»; if d=^i.2,d', n' = •2.271, but the undulations have now become so sweep- 

 ing that a ratio can only be inferred for the small coronas. 



5. Cause of periodicity. — If one inquires into the cause of the periodic dis- 

 crepancies, it appears that the crimson coronas are too small or else the green 

 coronas too large, for the data computed from exhaustions cannot be periodic. 

 The former being white-centered with a diffuse red margin, it is impossible to 

 mistake the outside edge of the first ring for the inside edge. The blue-green 

 coronas, however, show a uniformly colored disc, and here the first ring may 

 be of the same color as the disc, and the corona would then be measured to the 

 outside margin of the first ring. From this point of view only the crimson 

 coronas are adapted for measurement, and both curves would then give d=i.^d, 

 and »' = 2.2«. Since the cui-ves actually give evidence of diminishing aper- 

 ture while the droplets certainl)' decrease in size, this explanation is plausible, 

 though it does not agree well with the evidence from normal coronas. The red 

 and crimson coronas are the only ones which retain the white center, and the 

 phenomenon may in so far be regarded as similar to the case of normal coronas. 



6. Effect of temperature. — The explanation of the discrepancy between 

 d and d' (computed from exhaustions and measured from apertures, respectively) 

 reduces in the most favorable case to d = i.2,d', and for this two explanations 

 must be examined. Supposing that one does not inadvertently measure into 

 a ring, the value of m which enters into the computation of d is very variable 

 with temperature. For 6p=i'j cm., for instance, 



at 10°, m = 3.7 X iC* grams per cub. cm. 



20°, 4.6Xio-<^ " " " 



30°, S-7XIO-' " " " " 



Since d varies as m'^\ for the same nucleation the values of d at io°, 20°, 

 30°, will be in the ratio of 56, 60, 64, respectively, and the coronas will be in 

 the same degree smaller. Per degree between 20° and 30° this amounts to 

 about .8 per cent, of the value at 20°. Hence to bring the values of d computed 

 from successive exhaustions into coincidence with the data computed from 



