on the Optical Phenomena of the Atmosphere. 103 



in great splendour. On the masses of dolomite in the Fassathal 

 we observed the same twice. 



A -related phenomenon, which we had the opportunity of ob- 

 serving, deserves to be mentioned here. From the crest of the 

 Wildspitze, on the 18th of September 184-7, we had a fine pro- 

 spect towards the north. The entire series of the northern lime- 

 stone alps, from Salzburg to the Bodensee, was unfolded before 

 us with extraordinary clearness. In the mean time a storm 

 blowing towards the north increased in violence, and before we 

 attained the summit (11,489 P. F.) the northern mountains 

 exhibited an extraordinary colour. They had obtained a deci-' 

 dedly red tone, although the sun stood high, it being but 3 o'clock 

 in the afternoon. We had left the summit scarcely half an hour, 

 when immense cloud-masses were driven upon us from the side at 

 which the red colouring had been observed. During this time the 

 barometer fell considerably. It seemed as if the watery vapour 

 of the atmosphere, during its gradual condensation to mist, had 

 occasioned the redness in the same manner as the morning and 

 the evening red is produced. For the observation of this phse- 

 nomenon, it is first of all necessary that large masses of air 

 should lie between the observer and the object ; in the present 

 case the distance amounted to eleven or twelve miles (German) . 

 It is only from a high position that objects distant enough, and 

 with surfaces large enough to exhibit the modification of colour, 

 can be observed. Opportunities to see the phamomenon occur 

 but rarely, as it is but seldom that the observer finds himself at 

 such elevations during similar states of the weather. The colour 

 was not the shining red of the evening, but more of a purplish- 

 blue tinge, undimmed by fog of any kind, and in the production 

 of which the gray colouring of the limestone masses had a share. 



Direct sunlight, when it passes through mist, has also a red 

 tone imparted to it ; but the colours of rocks, &c. being the pro- 

 ducts of reflected light, disappear long before the red tone can 

 be assumed. We have in some cases endeavoured to determine 

 the intensity of the red which occurs on the passage of the light 

 through fog. 



Colour of Fogs with transmitted Light. 



