1884.] J. Bridges Lee — A peculiar atmospheric phenomenon. 5 



that the colours seen through a spectroscope are pure. The remarkable 

 circumstance about the phenomenon is that the more refrangible tints 

 were visible nearest to the horizon and the less refrangible tints above. 



No explanation has, I believe, ever been offered to account for this 

 peculiar atmospheric phenomenon, and, so far as I am aware, the phenome- 

 non itself has not been noticed in any standard work of science. The 

 very beautiful orange and golden sunsets which are so common during 

 the rainy season have of course often been noticed, and the explanation 

 commonly offered is simple and satisfactory. The chief facts noticeable 

 about a rosy sunset are that the atmosphere is charged with moisture, 

 and the deeper and less refrangible polours are found nearest to the 

 horizon. All other tints may be visible at various angular elevations and 

 all shades of colour, which are often beautiful beyond description, are 

 reflected from and transmitted by the clouds which commonly accompany 

 such a sunset. The colours are known to be due to the presence of 

 aqueous vapour and of very tiny globules of water diffused through and 

 suspended in the atmosphere. Violet waves which have the smallest 

 amplitude are first arrested and partly quenched and partly diffused. 

 Afterwards, indigo, blue, green, yellow, orange and red in the reverse order 

 of the spectrum. All are arrested and scattered more or less, but the most 

 refrangible rays are relatively most affected, while the longer and larger 

 waves force their way through. It follows that where the sun's rays 

 have had to pass through the densest masses of vapour- charged atmo- 

 sphere the least refrangible rays will preponderate. The layer nearest to 

 the earth will generally be most densely charged, and will present the 

 greatest thickness of air for the sun's rays to traverse, and the sun itself 

 and the western horizon will often appear of a deep blood-red colour. 

 Higher up the colours will be orange and yellow, or, if the atmosphere is 

 not highly charged, the horizon itself may appear orange or yellow, from 

 the fact that the yellow and orange rays are abundant, and the yellow 

 rays which lie nearest to the centre of the visible spectrum affect our eyes 

 more powerfully than the less refrangible red which lies near the lower 

 limits of visual sensation. Other tints which are visible on such occa- 

 sions are due to the bandying about of variously tinted light from cloud 

 to cloud and the various effects of dispersion, absorption and refraction. 

 These remarks, however, all refer to the well known appearances which 

 always accompany a fine sunset in the rainy season, and they are only 

 referred to for the purpose of drawing attention to the chief points of 

 difference between such a sunset and such a glow as we have lately seen in 

 the western sky. A different explanation is needed for what is quite a 

 different phenomenon, and I would suggest that the true explanation may 

 perhaps be elicited from a consideration of the different circumstances 



