1883.] On the Theory of Phosphorescence . 709 
The author refers here to the experiments of Becquerel, 
who proved that sodium sulphide and copper sulphate, on 
meeting in very narrow slits, formed not copper sulphide, 
but metallic copper. 
Whether oxygen, dissolved or in unstable combination 
when passing through capillary vessels, may, under the 
influence of the electro-capillary current, be capable of causing 
phosphorescence can only be proved by further experiments. 
Some of the above questions having a direct bearing upon 
phosphorescence were studied by the author during the 
spring of 1881, at the Naples Aquarium, where he had the 
opportunity of examining several hundred specimens of 
Pelagia noctiluca , Beroe ovatus, &c. 
The results of his experiments may be summed up as 
follows : — All the animals examined had an alkaline re- 
action, but the base which occasions this alkalinity could 
not be isolated. From the purified alcoholic extract of 
Pelagia noctiluca he succeeded once in obtaining a precipi- 
tate with gold chloride, but it underwent decomposition 
during re-crystallisation. The luminous substance of Pela- 
gia noctiluca is evidently a fat. The residue from the evapo- 
ration of 180 specimens of Pelagia noctiluca was extracted 
with ether, and yielded a body having the following proper- 
ties : — It is a syrupy, slightly yellowish, neutral liquid, easily 
saponified by alkalies. If kept for some time under the 
exsiccator it becomes harder, and almost assumes the con- 
sistence of butter. It is sparingly soluble in alcohol, readily 
in ether, but absolutely insoluble in water. If mixed with 
neurine or potassa this fat gives, when shaken, phosphor- 
escent flashes. Living specimens of Pelagia noctiluca 
behave in the same manner. In the Lazulite Grotto, in the 
Isle of Capri, the author saw thousands of specimens 
floating upon the surface of the sea. When undisturbed 
they were not luminous, but if excited by throwing them 
from the one hand to the other they gave off phosphorescent 
flashes, similar in colour and intensity to those obtained from 
the fat above mentioned. 
Finally, to prove the presence of active oxygen, the author 
used plates of plaster and clay, burnt and soaked in 
potassium iodide and starch-paste, tincture of guaiacum, 
&c. As Panceir had proved that the epithelial cells are the 
seat of the luminosity, either the entire animal or the 
luminous surface, prepared as quickly as possible, was laid 
upon the plates. The results were in every case affirmative. 
It must, however, be mentioned that the well-known colour 
reaction was produced most distinctly at the margin of and 
