56 THE BOOK OF NATURE STUDY 



are at first yellow, passing through green into the pale blue sky 

 above, but, as the sun sinks, the belt becomes narrower and 

 passes through orange to red. As this fades a pale light remains, 

 and during summer nights in our latitudes this pale light does 

 not completely disappear till the dawn twilight comes, so that we 

 never have complete darkness. 



At the same time that the colours appear in the western 

 horizon, the eastern sky is also affected. Here on clear evenings 

 what is called the twilight arch appears, this being a low flat arch 

 of pinkish colour, below which blue sky can be seen. 



In a letter written to Renan, the French chemist Berthelot 

 gives a very beautiful description of a sunset. We quote here in 

 translation the relevant passages, to show how nearly an actual 

 sunset may approach to the ideal conditions as outlined above. 

 The quotation may further serve as a model for similar descrip- 

 tions to be written by the pupils from their own observations. It 

 will be noticed that Berthelot, with a skill more frequent in French 

 than in British scientists, has contrived to give an accurate 

 description of the sequence of events, while producing at the 

 same time a beautiful piece of literary composition. In the 

 translation only passages which relate to the condition of the 

 sky have been included : 



" From the Place de la Concorde, with its leaping waters, one 

 saw in the first place in the western sky the fiery red mass surround- 

 ing the sun, already sunk to the horizon. It was not that this 

 light owed its beauty to its dazzling brilliancy, but it had an 

 indescribably soft and rosy tint, which was very soothing to 

 the eye, and which was reflected in the clouds of the opposite 

 sky. Here the reflected rosy tint faded gradually away, so mingling 

 with the natural colour of the clouds as to take on lovely purplish 

 tones. ... At this moment the sun, now completely beneath the 

 horizon, illuminated the western sky with a brighter glow. From 

 the bosom of this fiery expanse there radiated to north and south 

 four immense horizontal clouds, and the light was reflected to 

 the most distant points of the eastern clouds. Soon only the 

 four clouds remained brilliant, like four columns of fire, in the 

 centre of a white sky, partly masked throughout by a huge 

 greyish cloud and by the columns of smoke which rose from the 



