198 THE CHEMISTRY OF CREATION. 



new and pure white, nevertheless appeared to 

 be stained of a bluish colour, and the sea was 

 of a dingy yellow. On the first arrival from 

 the West Indies, we heard of the devastation 

 at Barbados; but with us there were no sub- 

 sequent unusual appearances ; on the contrary, 

 we had very fair weather, although 1 heard this 

 singular blue colour was observed even to the 

 coast." This letter was read by Sir D. Brewster, 

 at the tenth meeting of the British Association ; 

 and in alluding to the cause of the phenomena, 

 he expressed the conviction that the blue colour 

 was produced by the interposition of water, in 

 the form of vapour, between the sun and the 

 observer. 



It has been ascertained by M. Arago, that 

 the light thus reflected from the sky is in the 

 peculiar condition known by chemists as polar- 

 ised, exhibiting different effects from that of 

 the direct rays of the sun. Upon one of the 

 peculiar phenomena exhibited by the polarised 

 light of the sky as the sun changes its position 

 during the day, Professor Wheatstone has con- 

 structed what he calls the Polar clock or dial. 

 It is impossible in this place to enter into an 

 explanation of the principles upon which this 

 beautiful invention depends, as it would be 

 unintelligible without a full discussion of the 

 difficult subject of polarisation of light; but it 



