of this that can be given is probably to be found
in the fact that the chemical process ascertained to go on in the
phosphorescence of organic compounds on which experiments were made in
the laboratory is an extremely slow one.

The so-called phosphorescence of most inorganic bodies is one of a
totally different nature from that exhibited in organic forms. The
diamond shines for a time in the dark after it has been exposed to the
sun; so do pieces of quartz when rubbed together, and powdered
fluor-spar when heated shines with considerable brilliancy. Various
artificial compounds, such as sulphide of calcium (Canton's
phosphorus, as it is called from the discoverer), sulphate of barium
(Bologna stone, or Bologna phosphorus), sulphide of strontium, etc.,
after being illuminated by the rays of the sun, give out in the dark a
beautiful phosphorescence, green, blue, violet, orange, red, according
to circumstances. The luminous paint which has recently attracted so
much attention is of the same nature. In these cases what we have is
either a conversion of heat rays into light rays (as in the powdered
fluor-spar), or the absorption and giving out again of sun-rays. In
the latter case the phenomenon is essentially the same as
fluorescence, in which the dark rays of the solar spectrum beyond the
violet are made visible.

But we must now return to the other questions that have been started
in relation to phosphorescence in animals. There has been much
speculation as to the object of this light, and to the purposes it
serves in Nature. Probably no general answer can be given to this
question. It is no doubt impossible to show why so many animals have
been endowed with this remarkable property; but we may consider some
of the effects which the possession of it has in different cases.

In the first place, it will undoubtedly serve in many cases to afford
light to enable the animal to see by, and in the Lampyridae it would
seem that the degree of luminosity is related to the development of
the vision. In that family, according to the Rev. H.S. Gorham, the
eyes are developed, as a rule, in inverse proportion to the
luminosity. Where there is an ample supply of this kind of light the
eyes are small, but where the light is insignificant the eyes are
large by way of compensation. And moreover, where both eyes and light
are small, then the antennae are large and feathery, so that the
deficiency in the sense of sight is made up for by