Year: 1870

entllc world as the development OF the
spectroscope and spectrum analysis. So
great is the delicacy of this method of
analysis that by its aid we may pass be-
yond this planet and analyze the sun and
stars; and it is here that we find the most
important use of the instrument, which
thus supplies want long felt, and which
nothing hitherto has been able to supply.


The foundation of spectrum analysis
was laid by Newton, who first discovered
that white light was composed of rays of
all the primitive colors, different rays hav-
ing different degrees of refrangibility and
different properties. 1t was afterwards
discovered that one species of ray gave
more light, another more heat, while still
another yielded greater chemical force.
The separation of these different rays is
effected by passing white light through
prism, when, owing to the different de-
grees of refrangibility of the rays COM
posing it, the light is broken up, forming
what to us is familiar as the continuous
spectrum. Wallaston, by using very
narrow slit instead of the round hole used
by Newton, to admit the sunlight, obtain
ed "a spectrum similar in other respects.
but with this remarkable difference: the
spectrum in certain places was crossed by
dark lines or bands, which pure white light
did not give; what these lines mean we
shall see hereafter. But to Bunsen and
kirchof belongs the credit of establishing
the spectrum analysis on sure version by
examining the light given forth by differ
ent elements when in the form OF incan-
descent gases. The elements, when
brought into this condition and examined
by the spectroscope, were seen to show
lines, each having marked difference OF
position, and colors to correspond to their
positions when compared with the spect-
rum of white light, SO that the spectrum
of an element once noticed and recorded,
it could be easily recognised again.


Among the advantages of this system of
analysis over ordinary methods, are the
possibility of detecting any element in the
presence of any or all of the others, its
extreme delicacy and its adaptability to
to analyzing bodies which are inaecessi-
BILE, provided only that incandesence can
be obtained, Il condition present in the
state of the sun and stars. But it occurs
to us now to ask: What can we discover
from the spectrum of sunlight which is
continuous, being crossed only by dark
lines? DO these dark lines show any
thingp 1t was observed that many of the


lines in the solar spectrum had nearly or
exactly the same position as the lines of
some of the elements. Kirchoff set to
work to investigate the matter, confining
his experiments at first to the sodium line,
a bright band of yellow. He let q ray of
sunlight pass into his spectroscope, thus
obtaining the dark line in the solar spec
trum; he then placed the sodium flame
before his spectroscope and saw the dark
line pass into the regular yellow line
t1f in, t,xytra .pp1 crr1fr a
intensity of his ray of sunlight, this bright
line gave place to the dark line in the So
lar spectrum. Then he used calcium
light, which gives continuous spectrum,
from dark bands; this, when passed
through sodium flame, was crossed by
the same dark line. The matter was ex-
planned in this way A flame absorbs rays
of the same degree OF refrangibility as
that which it emts, fact proved in sew
eral ways by practical experiments. Then,
as the calcium light meets the sodium
flames, the latter allows all the light to
pass except that portion which has the
same degree of retrangibility as itself; !;
this portion is obstructed in the same way
that sunlight would be by any Opaque
body, and in the same way n dark space is
formed in the spectrum. The application
Of this, as applied to sunlight, would be
that the sun is a glowing mass whose light
passes through an atmosphere of inean-
descent gasses, thus giving continuous
spectrum crossed by dark lines. Even
without further proof, we should almost
be led to accept this theory; but when we
add the fact that the four hundred and
fifty lines in the iron spectrum and also
those of other elements, are each replaced
by dark line in the solar spectrum,
agreeing exactly in position, breadth and
the like, each to each, the theory is estab-
lished without doubt. Indeed, the prob
ability of this being mere chance has been
estimated to be less than one in qnintill-
ion, so that we are justified in assuming
any dark line in the solar Spectrum as
representing the same thing that a colored


line in the same position would represent.


What has thus far been determined of the


composition of the sun is matter of de-
, tail and does not concern us here.


Nor are we limited to the sun in our OBJ


servations; moon and stars, all fall be-
meath our gaze. The moon as we should
expect gives the same spectrum as the
sun, showing merely reflected sunlight.
The stars, however, give various spectra,
differing from that of the sun and of each
, other. And it is particularly interesting
u toHSiucI INC HtDulst, WLoSt IlSnl ID 81
feeble is to be almost imperceptible; yet
even these are analysed by the spectre
t scope, although the intensity OF the light
! is estimated to be but one two-thousandth
of that of a candle placed at a distance of
a quarter of mile, showing the delicacy
/, of which the instrument is capable. Even
the light OF a FREELY has been analysed by
9 means of the spectroscope, and is found
. to show a continuous spectrum composed


almost entirely of luminous rays, showing


that this insect, in giving so great rcla-
Q tive quantity of light, loses little or almost
d no heat. We must remember that the


specnoscope is as yet in its infancy, and
It what its future may be we can not fully
d determine; but it is certain that it must
4 hold its place in the front rank of scien-


tilic instruments, both on account of what


it shows of the chemistry of the sun and
\ stars, and from its terrestrial chemical
e discoveries. -1echnotogist.