It is a well-known fact that various bodies and compositions of matter,
more especially compositions containing sulphur in combination with
earthy salts, possess the property of emitting rays of light in the
dark after having been exposed to sun-light. All of these bodies and
compositions of matter are, however, not well adapted for practical
purposes, because the light emitted by them is either too feeble to be
of any practicable utility, or because the luminous condition is not
of sufficient duration, or because the substances are decomposed by
exposure to the atmosphere.
Among the materials which have been employed with the best results
for producing these luminous compositions are sea-shells, especially
oyster-shells. I have found by practical experiments that only the inner
surface of these shells is of considerable value in the production
of luminous compositions, while the body of the shell, although
substantially of the same chemical composition, does not, to any
appreciable extent, aid in producing the desired result. It follows from
this observation that the smallest shells, which contain the largest
surface as compared with their cubic contents, will be best adapted for
this purpose.
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