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utmost precision would be requisite to confirm tlie varying 
opinions to wliicli we have just referred. It would be neces- 
sary to demonstrate, with the aid of the microscope, that the 
objects perceptible to the eye were ova, and not Noctilucoe or 
some similar animalcules ; and to prove, by means of the same 
instrument, the existence of an organic deposit, or, in the 
latter case, it would have to be shown that the water was still 
phosphorescent after passing through the filter. 
But even if the accuracy of the theories propounded by 
Newland and M. Becquerel could be proved by observation 
and experience, in certain special cases, it would still remain 
an undoubted fact that the phenomenon of which we are treat- 
ing is essentially due to the presence, in great numbers, of 
Noctilucm. 
All the researches of the past century, therefore, lead us 
back to the conclusion arrived at by Rigaut as early as the 
year 1764. 
3. Nature op the Luminosity exhibited by Marine 
Phosphorescent Animals. 
In a paper printed nearly twenty years since, and the 
first one published by me on the subject,* I remarked that 
under the designation of phosphorescence there had been 
grouped together phenomena essentially distinct from one 
another, and having nothing in common excepting the pro- 
duction of light. In severing fluorescence, and studying it as 
a distinct phenomenon, physicists have to some extent dimi- 
nished the perplexity arising from the too general use of the 
former expression {i.e. phosphorescence) ; but the abuse of the 
term phosphorescence still exists, and nowhere is this so 
palpable as when it comes to be applied to the property 
possessed by certain living or dead organisms, of emitting 
light. Without dwelling upon the consideration of plant-forms, 
or upon that of animals deprived of vitality, we shall find that 
the production of fight hi the latter may be the result of vital 
actions of very different kinds. 
Let us first briefly call to mind the principal views that have 
been enunciated on the subject. Amongst the numerous 
theories that have been propounded in order to account for the 
existence of phosphorescence in living animals, there are some 
that need only be mentioned to be dismissed. 
In this category may be placed those of Beccaria, Mayer, 
&c., which assimilate it to fluorescence , t and who believe that 
the creatures emit at night the portion of the sun's rays which 
* On a new mode of phosphorescence observed in Annelides and Ophiu- 
ridfe . — Annales des Sciences Naturdles, 1843. 
t Fluorescence is, “ the diffusion of fight and change of colour -which 
