Luminous jinimals. 253 



to a bright light in a glass of water, will yield a very brilliant 

 and large spark. Thus, in a ship's bucket, or a basin, it would 

 not be conjectured that any animal existed, when many thou- 

 sands are present; and, of these, perhaps the greater number, 

 if not all, highly luminous. 



It is, lastly, necessary to remark, respecting the size of these 

 animals, as just mentioned, that many of the luminous species 

 are absolutely, and under all circumstances, except when in the 

 act of emitting light, invisible to the naked eye. This effect 

 arises in some measure from the actual minuteness of many, 

 their size not equalling the 100th of an inch; but in many 

 others which subtend a visible angle, it proceeds from their 

 transparency. Even under favourable circumstances, as when 

 placed in a glass of water, where the vision is aided by the mag- 

 nifying power of this species of lens, they cannot easily be 

 discovered ; owing to the water in which they abound being 

 invariably muddy. Those only come into view which ap- 

 proach so near to the fore part of the glass as materially to 

 diminish the column of water between them and the eye ; and 

 thus also they often escape observation, and the spectator is 

 surprised to find that he can discover nothing in the light, 

 when the water, in the dark, has abounded in luminous sparks. 

 If the lens is used, it is still only in the observer's power to get 

 sight of those which pass across its focus ; so that he is, in this 

 case also, apt to underrate their numbers, or, if rare, to doubt 

 their existence. It is fruitless to attempt to bring them under 

 the eye by using a small drop of water in the manner adopted 

 in microscopic observations ; as, even where most crowded, 

 they bear so small a proportion to the water in which they swim, 

 that such a drop may not possibly contain one. 



These then are the most important circumstances which the 

 naturalist should have in view in investigating the water of 

 the sea for the purpose of discovering the minute animals which 

 exist in it ; whether for the purpose of ascertaining their lumin- 

 ous quality, or of examining their nature and structure. An 

 attention to these cautions will probably assist others, as it did 

 myself in these examinations; and induce them to believe what 



