1867.] On the Luminosity of the Sea. 501 



over, but a close inspection revealed nothing in the water but 

 a few minute entomostraca. On another occasion when some water 

 which had been left in a basin exhibited luminosity at night, I got 

 a very brilliant spark upon my finger, and taking it to the light, it 

 proved to be a minute crustacean. 



The second form of luminosity to be noticed occurs com- 

 paratively rarely. It consists of a soft, usually greenish light, 

 which only makes its appearance when smooth water is disturbed, 

 and is only seen in calm weather. This form appears identical 

 with what we see nearer home, as on the shores of Ostend and in 

 the estuary of the Mersey. This form of luminosity I have 

 observed on only three occasions, and under similar circumstances, 

 and I have reason to believe that the cause is the same on all 

 occasions, whether in the Eastern seas or in the Mersey. On the 

 5th of July being on the coast of China, in lat. 27°, the weather 

 in the afternoon became dead calm, and after sunset I remarked 

 that the sea was beautifully luminous, but altogether without con- 

 spicuous sparks or points of light. Wherever the ripples caused 

 by the advancing ship rolled away, they were crested with bright 

 green light, and the ship's hull appeared to be enveloped in a 

 luminous sheath. On this occasion the effect did not last long, 

 and I did not examine the water microscopically. 



The next time I noticed this form of luminosity was in 

 Singapore harbour, on November 6th. The wind was east, 

 thermometer 76°, weather fine. The water was like glass, smooth 

 and beautiful, but exhibited no light except when disturbed; but 

 every oar-stroke of the boat in which I rowed produced eddying 

 circles of light, and a lovely soft green glow crowned every ripple 

 from the bows. A splash in the water produced a shower of 

 a myriad minute sparks, the aggregate of which made up this 

 delicate luminosity, which I never saw so beautifully exhibited as 

 upon this night. The following night the same effect was visible, 

 but scarcely so intense as before (wind N.E., temp. 76°), and on 

 the third night (the wind being E. and temp. 75°), I again 

 observed it. After this I was absent from Singapore two nights, 

 and on my return I no longer noticed the luminous effect. 



On each of these three nights, I examined the water ; — as I filled 

 a bottle, bright sparks of light adhered to my hands, and on bringing 

 it to the light I found that it contained a number of small globular 

 greenish bodies, which floated upon the surface for the most part, 

 but appeared to have the power of freely moving in the water. On 

 closer examination these bodies proved to be Nockilucee ; and during 

 the night I observed that the contents of the bottle frequently 

 flashed with bright and rapid coruscations. I had no difficulty 

 therefore in coming to the conclusion that the peculiar luminosity 

 in the harbour was due to the presence of innumerable Nodilucse. 



