PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 225 



bluish light; and, further, this blue light is polarized ni the same way 

 as the light from the small particles in the experiments with li([uids. 



While this explanation helps us so fiir to understand the manner in 

 which the yellow light is produced in steam jets, yet it fails to explain 

 the succession of colors seen in the expansion experiments, where blue 

 tirst appears, then green and yellow; and when the expansion is still 

 further increased, the blue again returns to give place to a second green 

 and yellow. The most probable explanation of these color phenomena 

 is that they are produced in the same way as the colors in plates, some- 

 what after the manner jSTewton thought the color of the sky was pro- 

 duced. The order of succession of the colors in thin plates is the same 

 as in these condensation i^henomena. As no white ibllows the first 

 blue, it seems probable that the first spectrum, or order of colors, is 

 not observed; that the two generally seen are the second and third. 



Some experiments were made with a glass tube receiver, in place of 

 the metal one, to see if there were any colored light reflected in these 

 expansion experiments of the same kind as is seen under certain con- 

 ditions in a steam jet; but no such colors have been observed. It is 

 possible they may be present; Init, owing to the great amount of white 

 light reflected by the larger particles, any colored reflected light that 

 may be present is masked. 



Green sun. — On a few occasions the sun has been observed to be of a 

 decidedly greenish color, while on other occasions it has appeared blue. 

 The experiments which have been described in this paper seem to offer 

 an explanation of this phenomenon. For a number of days in the begin- 

 ning of September, 18S3, the sun was seen of a decidedly blue or green 

 color in India, Trinidad, and other places. Most of the observers who 

 ImAC written on the subject have linked tliis phenomenon with the erup- 

 tion of Krakatao, which took place just before the days on wliich the 

 green or blue sun was seen. From the light thrown on the subject by 

 these experiments, we see that an eruption, such as that of Krakatao, 

 would throw into the atmosphere a supply of the very materials neces- 

 sary for producing a green sun by means of small drops of water, as it 

 would send into the atmosphere an immense quantity of aqueous vapor 

 and an enormous amount of hue dust — a combination the most favor- 

 able possible for producing a great number of minute drops of water. 



Prof. C. Michie Smith observed the green sun in India, and he says: 



" The main features of the spectrum taken on the sun when green 

 were : 



''1. A very strong general absorption in the red end. 



*' 2. A great development of the rain-bauds and of all other lines that 

 are ascribed to the i)resence of water vapor in the atmosphere."* 



It is evident, therefore, that one of the materials necessary for pro- 

 ducing this peculiar absorption by means of water drops was present 

 in an unusual amount in the atmosphere at the time ; and it also 



^ yatiirc, Auj;-. 7, 1884; vol. xxx, p. 347. 

 §Ml)3— 15 



