310 C. Barns — Successive Cycles of Coronas. 



2. The violet and green coronas. — As has been suggested, 

 the object of the series of experiments made at very low 

 exhaustions (drop of pressure Sj> = 10 cm ) and compared with a 

 series for high exhaustions (Sp = 205 cra ) was an estimation of 

 the importance of the time effect and of the convective effect 

 in causing loss of nuclei. If the latter series be reduced to 

 the former by modifying the constants in terms of pressure 

 and temperature, the coincidence of the graphs was found to 

 be complete. This indicates that the method of reduction is 

 reliable. 



To determine in how far the results themselves are trust- 

 worthy, it will be necessary to find the computed values in the 

 different independent series of measurements, of the diameter 

 of the fog particles producing a given corona. For this pur- 

 pose the violet (v) and green coronas (g) are suitable, the red 

 (?') less so. There are three of the green coronas, the two 

 upper being very brilliant. In a former paper the diameters 

 of particles were estimated as d — "0004 60 cm for the middle 

 green corona. Ratios of 4, 3, 2 were usually apparent, _ the 

 data being multiples of a diameter something larger than 

 d = 0001 5 cm , the corona for which is not producible in the fog 

 chamber. In the present experiments the values of the diam- 

 eter of fog particle d and s, the aperture of the green coronas, 

 still show considerable fluctuation ; but the data approach 

 closely to a common mean, remembering that the color itself 

 has a certain latitude, necessarily, and wdde differences of 

 exhaustion are involved in the tests. The ratio 2, 3, 4 of 

 diameters of fog particles is not as well suggested in the pres- 

 ent results as in the former, while the absolute sizes themselves 

 are throughout smaller. It is nevertheless convenient to retain 

 these ratios for the division of coronas into successive cycles. 

 If these may be considered as beginning with deep red and 

 ending with violet, the following cycles may be postulated, the 

 subscriDts denoting the order : 



i) Jt (d= -00011) v„, d— -00019 v 3 , d= -00033 v^d = -00044 om 

 ^,(^=•00013) g„ 23 g v 40 9o 52 cm 



»•„ (d= -00016) r„, 32 r s , 48 r v 64 cm 



Only the red and crimson of the first series are certainly 

 observable in any apparatus known to me. Their aperture, 

 s/30, is about 40 degrees, their rings diffuse and their disc filmy, 

 so that in a small apparatus they might be mistaken for clear 

 air. The second series is producible and vivid throughout, 

 and the same is even more true of the third. The fourth is 

 already closely packed, while the fifth and subsequent series 

 merge into each other too rapidly for separation. 



