282 
POPULAR SCIENCE REVIEW. 
animals ; not, in tliis instance, to Crustaceans, but to Nocti- 
lucce. 
We shall presently revert to the special consideration of 
these singular forms of life, which play so important a part in one 
of the most splendid phenomena afforded by Nature. Let us 
be satisfied, at present, with observing that the Noctilucie pre- 
sent the shape of little spherules, or rather of diminutive 
melons, whose largest diameter is one-third or half a milli- 
metre.* Their specific gravity is rather less than that of sea- 
water. Allowed to rest in a liquid which is in a perfectly un- 
disturbed state, they form a layer or coating at the surface, just 
in the same manner as a number of corks would do ; but the 
least agitation mixes them up with the fluid which before sup- 
ported them at the surface. 
Now, them number is so great that it suffices to produce all 
the appearances already indicated. Of this the following figures 
will afford a sufficient proof. I once took some water from a 
very brilliant wave, and with it filled a tube, one decimetre 
(about four inches) in height. After it had been permitted to 
stand a few minutes, the layer formed by the aggregation of 
the Noctilucee was one and a half centimetres in thickness ; 
consequently the animalculas constituted a seventh of the whole 
mass of fluid. On drawing the water from the surface only of 
a wave just breaking upon the beach (skimming it, as cream is 
taken from the milk), I filled therewith a large goblet. The total 
height of the liquid was fifteen centimetres (between five and 
six inches) ; that of the layer of Noctilucae five centimetres, or 
about one-tliird of the mixture which I had collected. This is 
the highest ratio obtained by me; but at False Bay, M. de Tessau 
found the proportion of animalcule to be one-half. Without 
taking into consideration any diversity of species which may 
exist in those latitudes, this estimate of numbers alone suffices 
to account for the far greater brilliancy of the phosphorescence 
there, as compared with the phenomenon with us. It is easy 
to comprehend how so vast a multitude of luminous corpuscles, 
disseminated through a body of water, may present an illusory 
appearance to the eye, just, for example, as the fine molecules 
of earth, held in suspension in the liquid which they cloud, 
impart to it a distinct homogeneous colour. 
But here again are other experiments that place the ques- 
tion beyond all doubt. f 
* A metre, the French standard measure, is 39'33 inches ; a decimetre, 
centimetre, and millimetre are respectively the 1 Oth, 100th, and 1000th part 
of a m&tre. The diameter of Nodiluca is on the average one-fiftieth part of 
an inch. 
t Most of these experiments were first tried by Suriray, a doctor at Havre ; 
they were repeated by Blainville and M. de Tessau ; M. Verhaeghe added to 
them, and I myself repeated and diversified them in various ways. 
