1884.] J. Bridges Lee — A peculiar atmospheric phenomenon. 7 



they will be the most rapidly cooled, and the first condensation of water 

 to form fine mist of watery globnles or ice crystals, will be there. This 

 condensation of the uppermost layers once commenced will continue, and 

 the tiny globules or crystals will grow in dimensions and in number, while 

 at the same time condensation will be proceeding in a downward direc- 

 tion through successive layers of the atmosphere. Now if this theoreti- 

 cal account of what should occur in a still and cloudless atmosphere 

 represents what actually does occur, the explanation of the phenomenon 

 which we started by describing is not far to seek and is in perfect accordance 

 with the ordinary explanation of a rosy sunset. The rays which reach 

 the eye after travelling mostly through the lower layers of the atmosphere 

 will have lost least by absorption or diffusion, and the loss of violet, blue 

 and green will become greater in proportion as more of the upper layers 

 are traversed before the light reaches our eyes. The lowermost limit 

 which I observed last Sunday was, as above stated, green. The green was 

 a yellow green and shaded off into bright yellow. I am inclined to think 

 that the greenish tinge was due to the blue background of the sky ; which 

 was in fact visible through the yellow haze. Higher up there would ap- 

 pear to have been a denser glare and the blue background would appear 

 to have been completely obscured. Above that the yellow shaded off 

 through orange into red, which gradually faded off through purple towards 

 the dark blue of the sky. The purple I consider also to be due to the 

 fact that the blue sky was partially visible through the faint peripheral 

 red. 



Postscript. 



The above observations were written in the first week of November 

 when the phenomenon was particularly well marked. Since then the 

 same appearance has been observed several times apparently over wide 

 areas and many letters have been written to the newspapers referring 

 to the peculiar after-glow and advancing various theories, some of them 

 very wild and farfetched. Especially was it suggested that the phenome- 

 non might be connected with volcanic dust supposed to have been distri- 

 buted with marvellous uniformity through the upper layers of the atmo- 

 sphere, and over tens of thousands of square miles of superficial area. 

 Without going the length of suggesting that such an explanation must, 

 in the particular instances referred to, be necessarily unsound or incorrect 

 I would urge that the explanation above given is more rational and more 

 simple. We know of course that there are authentic instances on record 

 where volcanic dust has been distinctly traced to a distance of some hun- 

 dreds of miles from a centre of volcanic eruption, but in such cases well- 

 marked air-currents have had much to say to the distribution, and any- 

 thing like a uniform distribution of dust through the atmosphere a thou- 



