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British ^Association, 123 



with the calculation of the sun's progress) that the phaenomenon is 

 due to the rays of the sun whfch traverse the atmosphere at a dis- 

 tance from the earth less than the height of Mont Blanc, but greater 

 than half that height, and which arrive at rarer regions of the atmo- 

 sphere under an incidence so great that they are reflected instead of 

 refracted. This interior reflection is facilitated by the humidity of 

 that part of the atmosphere which the rays traverse until they reach 

 the point of incidence. The reflected rays falling on the snowy sum- 

 mit of Mont Blanc produce this second illumination; and the humi- 

 dity (by augmenting the transparency of the air) renders the illumi- 

 nation more brilliant. 



Sir D.Brewster stated that he had witnessed a similar effect, though 

 on a less magnificent scale, on the Grampian Hills ; but he had 

 always observed that on such occasions the sun set in a red west, and 

 that all the clouds in that quarter of the heavens were then red. — M.de 

 la Rive replied, that the pbanomenon he spoke of only appeared wher» 

 the sky was quite free from clouds, and, in truth, it was most brilliant 

 when the air was very transparent in consequence of its being loaded 

 with vapour in its elastic state. — Professor Lloyd said that the dis- 

 tinctness and vividness with which distant objects were seen in some 

 states of the atmosphere was quite astonishing : on one occasion he 

 had seen from the neighbourhood of Dublin the Welsh hills from their 

 very bases, and brought so near apparently, that he could absolutely 

 see the larger inequalities of the surface upon the sides of the moun- 

 tains. That the atmosphere was at the time very much loaded with 

 vapour in a highly transparent state, was obvious from the fact that 

 immediately after a very heavy fall of rain took place, and continued 

 for a considerable time. — Professor Stevelly wished to confirm what 

 had fallen from Professor Lloyd and M. de la Hive by stating that 

 whenever the Scotch hills appeared with that peculiar vividness and 

 distinctness, from the Lough of Belfast, the fishermen always looked 

 upon it as a sure precursor of heavy rain and wind. A friend had in- 

 formed him that on one occasion he had noticed this appearance 

 while standing on the beach at Hollywood, and pointed it out to an 

 old fisherman ; the old man immediately gave notice to all his friends 

 to whom he had access, who instantly set about drawing up their 

 boats and placing their small craft in more secure places ; early the 

 next morning a violent storm came on, which did much damage upon 

 the coast to those who had not been similarly forewarned. Thus we 

 find that the most interesting pursuits of the man of science, and the 

 most important concerns of man in the practical details of life, fre- 

 quently approach, and each may lend important aid to the other. — 

 Mr. Lubbock was of opinion, that the principal fact mentioned by M. 

 de la Rive would receive a simple solution, if we admit the theory of 

 Poisson regarding the constitution of the atmosphere. That eminent 

 mathematician conceived that analysis led irresistibly to the conclu- 

 sion that the upper portions of the atmosphere were, by the extreme 

 cold there existing, condensed into a liquid or even into a solid : if 

 this were so, we could easily conceive how the reflection of the light 

 from its under suiface would re-illuminate the top of Mont Blanc 

 after the direct light of the sun had ceased to reach it. — Sir David 



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