No. 5. [From Nature, July 21, 1910, Vol. LXXXIV. pp. 87-89.] 



THE COLOUR OF THE SEA 1 



APROPOS of the report (Nature, March 10) of Lord Rayleigh's 

 lecture dealing with the parts played by reflection and trans- 

 mission of light in the production of the integral impression 

 of colour on the eye of an observer looking at the sea from the 

 deck of a ship, I should like to be permitted to make some 

 observations on the proper colour of the water of the ocean, 

 as it is a subject which has occupied my attention, off and 

 on, during the last forty years. 



During the voyage of the "Challenger" I began to log 

 the colour of the water in February, 1874, when she was 

 working in the neighbourhood of the Antarctic circle. My 

 attention was there directed to it by the frequent and abrupt 

 passage of the ship from water of the clear indigo colour of 

 the ocean of temperate latitudes to the deep olive-green water 

 which is a distinctive feature of these icy regions. 



The green colour is due to the abundance of diatoms. These 

 are so plentiful and so preponderant that, besides putting 

 their stamp on the surface, they furnish a distinct type of 

 oceanic deposit, the diatom-ooze. The green colour of the 

 water is due, not only to the living diatoms, but also, and perhaps 

 to a greater extent, to the excretions of the animals for the 

 subsistence of which the diatoms furnish the ultimate food 

 supply. The crowds of penguins and other birds to be met 

 with in these seas stain all the ice green where they have 

 rested. The water, inhabited by diatoms and affected by 

 diatomaceous debris, has a deep olive-green colour which is 

 characteristic, and this I accepted as one colour-type of the 

 water of the ocean. It is seen best in the water the transparency 

 of which is not interfered with by too great a crowd of the 

 1 See Contents, p. xxiii. 



