( 500 ) [Oct., 



III. ON THE LUMINOSITY OF THE SEA. 



By Cuthbert Collixgwood, M.A., M.B., F.L.S. 



During my recent expeditions as Naturalist on board H.M.S. 

 'Serpent/ one of the subjects to which I was anxious to pay 

 especial attention was the luminosity exhibited by the sea, its 

 appearance and Yarious forms, the various conditions under which 

 it became manifest, and, as far as possible, the causes which pro- 

 duced it. These points have already engaged the attention of 

 observers, but much remains yet to be learned, nor shall I profess 

 to add a great deal to what is already known, but shall simply 

 relate the result of my observations carried on at every opportunity 

 during a year and a half. Not a night passed while I was at sea 

 without my looking out for luminous appearances — jotting down 

 anything novel or unusual, and where practicable, making an 

 examination for the detection of the cause of the luminous ap- 

 pearance ; — and although the moonlight nights were very beautiful, 

 I often bewailed the invisibility of the lu m inous animals whose 

 light was extinguished by the effulgence of the moon's rays, and 

 longed for a return of the dark nights when the brilliancy of the 

 stars compensated for the absence of the moon, without putting a 

 stop to my observations on the luminosity of the sea. 



I would classify all the cases of luminosity which have come 

 under my observation under the following five heads : — 



1. Sparks or points of light. 



2. A soft, liquid, phosphorescent effulgence. 



3. Moon-shaped patches of steady light. 



4. Instantaneous recurrent flashes. 



5. Milky sea. 



The first of these, or the appearance of points or sparks of 

 light, is by far the most common, and in different degrees may be 

 said to be all but universal. Whether the other forms of luminosity 

 are exhibited or not, sparks of light in greater or less abundance 

 are scarcely ever absent. The sea, more particularly when agitated, 

 sparkles with brilliant points of light, varying in size from that of 

 a pin's head to that of a pea — and of greater or lesser permanency — 

 some being almost instantly extinguished, while others retain their 

 light for an appreciable time. I do not think I ever looked at the 

 sea on a dark night without seeing some few sparks, even though 

 I might enter a remark that the sea was "not luminous to-night." 

 But usually these sparks are abundant, and on occasions they 

 present a wonderfully brilliant appearance. On one occasion, when 

 this phenomenon was unusually striking, on the coast of China in 

 lat. 26° N., on drawing up bottles full of water and pouring it out 

 in the dark, the water sparkled brightly as luminous points ran 



