This latter process is one of rapid oxidation.
The particles of carbon supplied by the oily matter that feeds the
candle become so rapidly combined with oxygen derived from the air
that a considerable amount of light, along with heat, is produced
thereby. Now, the phenomenon of phosphorescence in organic forms,
whether living or dead, appears also to be due to a process of
oxidation, but one that goes on much more slowly than in the case of a
lighted candle. It is thus more closely analogous to what is observed
in the element phosphorus itself, which owes its name (meaning
"light-bearer") to the fact that when exposed to the air at ordinary
temperatures it glows in the dark, in consequence of its becoming
slowly combined with oxygen.
At one time it was believed that the presence of oxygen was not
necessary to the exhibition of phosphorescence in organic forms, but
it has now been placed beyond doubt that this is a mistake. Oxygen has
been proved to be indispensable, and hence we see a reason for the
luminous organs in the glow-worm being so intimately connected, as
above mentioned, with the air-tubes that ramify through the insect.
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