196 THE CHEMISTRY OF CREATION. 



tiful a blue? The truth is, the air is not per- 

 fectly transparent when seen in bulk ; and the 

 cause of the blue colour is the reflection of the 

 rays of light from its particles, and from 

 those of the watery vapour it contains. As we 

 ascend, the colour deepens in intensity, in con- 

 sequence of the dark space beyond our atmo- 

 sphere being seen through it more distinctly, and 

 at the great elevations which have been attained 

 by means of the balloon it almost approaches a 

 black. On the summit of high mountains it is 

 often seen to be of an intense Prussian blue. 

 M. de Saussure made some singular observations 

 upon this subject, and formed a scale of the 

 shades of colour as we ascend. In Coleridge's 

 sublime lines, entitled the Alpine Hymn, this fact 

 is alluded to in speaking of the " Sovran Blanc." 



" Around thee and above 



Deep is the air, and dark, substantial black, 

 An ebon mass. Metliinks thou piercest it 

 As with a wedge." 



Sometimes, apparently in consequence of the 

 presence of a large quantity of water in the 

 air, the blueness becomes very remarkable. The 

 following letter describes a most curious ex- 

 ample of the occurrence of this phenomenon at 

 Bermuda: "On the 10th of August, 1831, 

 the weather," observes the writer, " was remark- 

 ably fair ; but as evening drew near, a change 



