Atmospheric Phenomena in Ceylon. 59 



land, but a veil of darkness suspended between the observer 

 and the low country. All this time it is rapidly rising and 

 approaching, and each instant becoming more distinct, until 

 suddenly it seems to fall back on the spectator, like a ladder 

 that has been reared beyond the vertical ; and the next instant 

 it is gone. Of the accuracy of the above facts I have no 

 doubt whatever. A great number of trustworthy witnesses 

 have described it to me ; and but for a sudden attack of fever 

 at the foot of the peak, which prevented an ascent being made 

 in the evening, I should have been able to describe it from 

 personal observation. As it was I ascended next day and was 

 able to form a very good idea of the conditions under which 

 the phenomenon takes place ; but I was, of course, unable to 

 obtain accurate data as to the duration of the veil, the height 

 to which its apex rises above the horizontal, the elevation of 

 the sun, &c. If I am right in supposing that no explanation 

 has ever been offered of this remarkable appearance, the follow- 

 ing remarks, which appear to be fairly satisfactory, may 

 perhaps not be uninteresting. The average temperature at 

 night in the low country, during the dry season when 

 Europeans ascend the mountain, is between 70° and 80° F., 

 whilst that on the summit of the peak is from 30° to 40° F. 

 Consequently the lower strata of air are much less dense than 

 the upper ; and an almost horizontal ray of light passing over 

 the summit, must of necessity be refracted upwards and suffer 

 total internal reflection as in the case of an ordinary mirage. 

 This may be readily seen by a reference to fig. 1, where a 



Kflf. 1. 



nearly horizontal ray passing over the summit of the peak P 

 suffers total internal reflection at A, and is deviated upwards 

 in the direction A B ; or when a less horizontal ray is refracted 

 at C, reflected at £>, and refracted again at E, it finally 

 issues along the line E F. It will be evident from fig. 1 that 

 the shaded parts represent the veil of darkness at three dif- 

 ferent moments of time, and also that the veil appears to rise 

 as its base approaches the mountain, i. e. as the sun rises and 

 the rays fall less horizontally. 



By referring to fig. 2 it will be seen how the aerial shadow 

 of the upper part of the peak, i. e. the part above A B, suffers 

 total internal reflection, and is thrown upwards into the air as 

 C E D. It will also be evident, by comparing the two figures, 



