C. Barus — Apertures of Coronas. 337 



sation chamber between them. This was here a tall cylindri- 

 cal vessel of as clear glass as- possible, 50 cm long and 13 cm in 

 diameter. The observations were made parallel to the axis, 

 absence of distortion being assumed for the axial plane, an 

 assumption which was here justified by a comparison with 

 plate glass apparatus, though the latter was not quite large 

 enough for the complete survey. The method of work was 

 otherwise the same as that described in my earlier papers. 



The constants of the goniometer were determined so that 

 s'd' = -0023 and n'= 120 s' 3 for the mean temperature 20° C. 

 Phosphorus nuclei were used throughout. The pressure decre- 

 ment on exhaustion was always Sp = 17 cm . 



The results of the tables are given in the accompanying 

 chart, in which the old results for diameter and aperture, d and 

 s, are laid off horizontally, the new results d' and s', computed 

 as stated from the observed apertures, vertically. The dis- 

 crepancy of the two sets of data is marked and the curves all 

 show sustained periodicity. 



3. Diameter of cloud jp article. — The variations of d and d' 

 are on the average 8d=l'4c8d' from curve 4, and hd = 1*6 

 hd' from curve 5. In other words, the diameters obtained for 

 coronas by computation from the conditions of successive 

 exhaustion are about 1*5 times larger than the same data esti- 

 mated directly from the apertures of the coronas. 



Moreover the new values of diameter, d\ show a curious 

 periodicity which must be peculiar to them, since the old 

 values from the manner in which they were obtained (geo- 

 metric progression) can not be periodic. There is accelerated 

 increase of diameter toward the crimson types, Nos. 9 and 14, 

 and a falling off which may even be a retrogression toward the 

 green types, Nos. 4-5, 11-12, 15-16, these being respectively 

 the crests and troughs of the wave. The undulation continues 

 even beyond this, but it is then difficult to identify it when the 

 annuli become crowded into the normal coronas. The results 

 are similar in all the experiments. Moreover the same undu- 

 latory line was encountered both for phosphorus and for water 

 nuclei, with maxima at the 9th and 14th coronas, when a dif- 

 ferent vessel (aspirator, 32 cm high, 22 cm in diameter) was used ; 

 and the ratio, 8d = 1*3 8d', was distinctly smaller for this case, 

 showing the marked influence of distortion due to the vessel. 

 The same ratio (1*3) was found in connection with the pre- 

 liminary experiments with plate glass apparatus (curve 3). 



4. Nucleation. — Since nd 3 is constant, remarks of the same 

 general character may be made for the nucleation, n, except 

 that the discrepancy will be reciprocal in character and enor- 

 mously exaggerated. If on the average d — 1*5 d\ n' = 3'4 n / 

 if d = I'd d', n' — 2*2 n. but the undulations have now become 



