COLOUR OF THE OCEAN. 267 



yellow from ferruginous depositions. Cal- 

 careous matters seldom affect their colour, 

 but often their transparency, when deposited, 

 as is the case with the Velino at Terni, and 

 the Anio at Tivoli; but I doubt if pure sa- 

 line matters, which are in themselves white, 

 ever change the tint of water. 



ORN. On what then does the tint of the 

 ocean depend, which has itself given name 

 to a colour? 



HAL. I think probably on vegetable mat- 

 ter, and perhaps, partially, on two elementary 

 principles, iodine and brome, which it cer- 

 tainly contains, though these are possibly the 

 results of decayed marine vegetables. These 

 give a yellow tint when dissolved in minute 

 portions in water, and this mixed with the 

 blue of pure water would occasion sea green. 

 I made many years ago, being on the Mer 

 de Glace, an experiment on this subject, 

 I threw a small quantity of iodine, a sub- 

 stance then recently discovered, into one of 

 those deep blue basins of water which are 

 so frequent on that glacier; and diffusing it 

 as it dissolved with a stick, I saw the water 



