C. Bar us — Successive Cycles of Coronas. 311 



Cycles 3 and 4 were obtained in great number in my work 

 with atmospheric nucleation. Selecting some twenty or more 

 cases, the mean ratio l/s 3 : l/s i = "146 : -206 = d 3 : d^. Hence 

 the ratio of 3:4 is very well sustained. The goniometer dis- 

 tance from the fog chamber was nearly a meter in this case. 

 Hence it is probable that the cycle 1 is actually the first occur- 

 ring, although the smallest active particles (violet) must exceed 

 •0001 cm in diameter. The same terminal conditions are sug- 

 gested by the axial colors of the steam jet. It seems curious 

 that the diffraction phenomenon should begin with particles of 

 the order of three times the wave length of light. 



Using the method of contact of coronas from two sources 

 described elsewhere,* the ratio of diameters of the four first 

 series is again very nearly as 1, 2, 3, 4, for the green coronas, 

 for instance. 



3. Wilso?i , sf data and conclusions. — The table contains 

 "Wilson's exhaustions (v,/v)' at 18° to 19° C. and the corre- 

 sponding disc colors, as I interpret them. It also contains the 



Estimate of the diameter of nuclei d and their number n per cm 3 corre- 

 sponding to Wilson's colors of cloudy condensation in wet dust-free air. 

 Temp. 18°-19°. 



l() 3 x Disc 10 5 x 10 6 x 10- 6 10" 6 



Vi/v dp/p color d 3 , 2 d- 2 , 1 n 3 , 2 n 2 , x 



1-410 384 green 40 23 -17 "900 



1-413 386 " 



1-419 390 violet 33 19 -27 Vo 



1-420 390 " 



1-426 394 red 32 16 "32 2'5 



1-469 418 greenish white 23 12 -90 7"0 



equivalent relative drop of pressure Bp/p used above. From 

 these and the colors of diameters of fog particles (d) may be 

 estimated, very roughly of course, provided the cycle in which 

 these colors lie is known ; hence d s ^ refers to the probable 

 case of the occurrence of the third and second series, d^\ to 

 the very improbable case of the occurrence of the second and 

 first series. If the values m be found for the corresponding 

 temperature and expansions {Bp/p), the nucleations 713,2 and 

 n-2.1 respectively follow. Wilson gives but a single cycle 

 between green coronas. There are two such series and three 

 definite large green coronas producible, and I shall assume 

 that the very vivid upper one is meant. The first cycle is not 

 producible by any means known to me, except in its lower 

 reel coronas. Ignoring w 2 ,i and taking w 3i2 , the data are dis- 



*This Journal, xxiv, p. 277. 1907. 



fPhil. Trans. Eoyal Soc, vol. 189, pp. 265, 1897 ; cf. p. 285. 



