appreciate the peculiar characteristics of each
individual light, from whatever radiant source
it reaches us.

If we put a glass prism in the course of a ray
of light, that light, by traversing the prism, is
decomposed into its primitive elements. It is
an experiment which may be tried any sunshiny
day; and sometimes an icicle, drawing-room
ornament, or a gem, will try it for us. At first
sight, the eye perceives a series of lovely hues
ranged one above the other, calling to mind the
colours of the rainbow, with which, in fact,
they are identical. On inspecting the party-
coloured ribbon so obtained more closely, we
discover, when the light comes from the sun,
hundreds of black stripes of extremest fineness.
When the light proceeds from an incandescent
solid or liquid body, the stripes disappear, and
the coloured ribbon or spectrum, is continuous.
If, on the contrary, the light is given out by
burning gas, bright and brilliant stripes appear
in the spectrum. If, lastly, the source of light
is an incandescent nucleus enclosed in a gaseous
envelope, the image, as is the case with the sun,
is traversed by a series of black lines.

Both the black and the brilliant lines were
long a puzzle to natural philosophers. In 1822
Herschell remarked that when salts of lime,
copper, and strontian were introduced into a
flame, luminous lines were produced in the
spectrum of that flame. Not long afterwards,
Brewster and Talbot ascertained that the
brilliant stripes varied with the nature of the body
put into the flame. Common salt, for instance,
gives a bright yellow stripe. Potash causes the
simultaneous appearance of a red stripe and a
violet stripe. It was clear, therefore, that the
bright lines of the spectrum resulted from the
presence of determinate compounds in the
flame. But what of the black stripes?

The labours of several other philosophers
helped Messieurs Kirchoff and Bunsen to
demonstrate undeniably, in 1860, that every
bright light in the spectrum is transformed into a
dark one, when a source of intense light exists
behind the flame. Example: soda gives a bright
yellow stripe. Put an electric light behind the
flame producing the spectrum, and instantly
the bright stripe disappears, to give place to a
corresponding black one. The fact is easily
accounted for, when we remember that the
property of emitting light, like that of radiating
heat, is combined with the property of absorbing
it in inverse proportion. The more light a
luminous object gives out, the less it will take
in. The more capable a flame is of emitting light,
the more does it, from that very circumstance,
extinguish a light placed behind it. It is therefore
clear that every line which is more luminous
than the neighbouring portions of the
spectrum of a flame, will necessarily become
darker as soon as a source of light is placed
behind it. Such is the answer to the black line
enigma.

But the spectrum of the solar light is cut
up and riddled with black lines through and
through. The conclusion is that incandescent
flames or vapours, containing a great number of
volatilised substances, surround the sun, and
that behind those flames there exists a source
of light still more powerful and intense than
they are. MM. Kirchoff and Bunsen carefully
examined the position of the lines produced in
the solar spectrum by the principal substances
found on the earth, and they then turned them
black by the application of a more intense
source of light. Now, they found that there
was an absolute identity in the situation and
distance of the black stripes in the solar
spectrum, and of the stripes thus artificially
produced. This precise coincidence allows us to
conclude the existence, both in the sun and the
earth, of certain constituent elements. The
light emitted by the sun indicates the presence
in it of iron, magnesium, sodium, potassium,
barium, copper, manganese, zinc, &c. Hitherto
they have been unable to ascertain the existence
of gold, silver, lead, tin, antimony,
cadmium, arsenic, mercury, &c.

We have thus a telegraph established
between the stars and ourselves. The telegrams
reach us in letters of fire. The lines of the
spectrum replace the letters of the alphabet.
Every element has its characteristic signs; but
the reading of this alphabet is very complicated,
and we have scarcely as yet begun to spell
it. Evidently discoveries will be greatly multiplied
when we have learnt to read it fluently.
Nevertheless the principal stars, comets (one of
which has been found to contain carbon), and
nebulae have already been explored with
considerable success.

It was an inevitable consequence of the
preceding facts that the habitable condition of the
sun is a fallacy, and that we do not see the
sun's soil at the bottom of his spots. Our
central life-giving luminary must consist of a
gaseous incandescent atmosphere containing
metallic vapours, inclosing a solid or liquid
burning nucleus. The spots in this case would
be veritable clouds, produced by the partial and
local condensation of solar vapours. There is
a discrepancy between Kirchoffs observations
and Arago's experiments on polarised light;
but the apparent contradiction has been
reconciled by an able French astronomer, M.
Faye. Kirchoffs spectral observations are
quite consistent with those afforded by a
perfectly gaseous sphere holding solid particles in
suspension.

The sun, therefore, must be set down as
neither solid nor liquid, but gaseous, as might
be inferred from its slight mean density. This
theory has the further philosophical advantage
of being applicable to the other heavenly
bodies, each one of which would pass through
successive phases corresponding to the divers
epochs of their evolution and progress. Each
heavenly body must successively experience
the gaseous, liquid, and solid states. The sun,
the earth, and the moon, for instance, offer us
the three distinct ages in the life of worlds.
The earth once must have been for the moon
what the sun is now for us. The moon's
smaller mass would sooner grow cold. Then
the earth, after having been what the sun is,