New-York tribune., 1873-02-03
THE SPECTROSCOPE.
LECTURE BY PROF. G. +. BARKER,

ANALYSES OF SOLIDS AND GASES.
The large hall of the Cooper Union was
densely thronged saturday evening, the occasion
being the delivery OF the second lecture Of the Cooper
Union free course of Scientific lectures The lecture
was the first OF series Of three by Prof George r.
Barker Of Yaet College the speOroscope and It's ap
plicatons. Promptly at O'Clock the lecturer mace MS
appearance and was warmly greeted The following Is |
an abstract OF the lecture
THE LECTURE
Men OF science not unirequentiy accumulate iac'S
which seem to OF value. but Dy Whleh Erhu IT,
anita are achieved What import to us that about
ten years since German chemist made few observa-
tons I'm his laboratory with pieces of colored glass
Yet as the result Of those observations we now may
wander around earth with small tube In our hands
examining all meet with; nay, MORE WIN
it we may ascend to the heavens ana 10
the limits of space and observe the constitutions
OF the celestial orbs These some OF the results OF e
observations made by heldistneuished chemist at he
deIburg This method Of investigation Is called spec
trum analysis and tho instrument by which the oDser-
va,ions are made Is the speooscoDe. propose IN this
evenings lecture to take up and explain the spectre
scope ITSELF to show the principles upon which IT'S
based the method Of using It, and the various xmas Oh
spectra obtained by such use. / shall lreIace
my remarks by stating few wenknOWn prin-
ciples of light. Light coming from any body
continues while in the medium in straight line,
be this medium what 1t may. But IL the medium
changes then the direction of the light also changed
II we pass a ray OF light proceeding from luminous
body into it is bent out OF Its course Inls
called refracton and was known to Newton. To test it
he made circular aperture ~ inches in diameter in
window shutter allowed the sunlight to enter, which
formed a round spot Of light on the floor. he then
placed a prism in the way of the light,
expecting to see the light bent out OF
It's course and an image OF the round spot Of light on the
opposite wall. He did this image on the wall, and
more Not round image but a heightened and colored
there 1t was, like the damater OF the hole IN
the shutter and oneourth inches in breadth, out IL
was ten and half inches longer. 1t coored, for
the white light had undergone change, and had sepa
rated into its component colors. Thus the spectrum
urst produced.
TIE SECRETS OF DISPERSION.
The method by which it accomplished Is called
dispersion The lecturer here threw number OF da-
grams on the screen illustrative OF the change Of direc-
tion which light undergocs upon entering different
medium.
The direction Of the emergent ray depends on the
shape OF the medium through which II passes When IL
passes through prism eoors appear IN ADDITION 10 the
change OF direction and the series in the order
Of red orange, yellow, green, blue. indigo and violet
A spectrum is the succession Of coors produced when
light is allowed to enter PRISM The lee
turer then allowed the light from the
carbon points at the extremities Of the
wires leading from the galvanic battery To pass through
prism flint glass, and the spectrum appeared on the
screen Then he showed the condition Of the carbon
points by rejecting image OF them on the screen Ihe
carbon which appeared on ScEtth bS
and which connected with the positive pole OF the bat
ferry was very bright while the other less so. The
speaker then placed diaphragm having circular open
ing in front of the camera. containing carbon ana
a round spot OF light appeared on the screen. Re
ferring to it the lecturer said this may represent
10 m the image of the opening the window shutter in
The experiment Of Newton. If we now place prism In
the path the Hight the spectrum as he obtained
st. necessary however to turn the lantern around
IN order that it may fall the This is necessary
fhoA AfCnar of he
containing substance greater dispersve power than
fint glass to the lantern still further The
Professor then employed prism containing bisuphide
carbon and the length OF the spectrum obtained was
Increased speaker then continued: The image on
the defective because the light came through
round opening. But, you observe, the longer the
spectrum perfect Is. In the middle OF the
spectra were however all the cOlOrs together forming
white light The fact is, cannot use round opening
for the purpose. long, opening, termed slit,
As used The slit also be vertical in order that
there shall be no overlapping of cOlOrs The experiment
OF producing a spectrum with the slit horizontally and
vertically was then performed In the latter only
was the spectrum entirely free from white light
Continuing the speaker said we may examine the
light by the eve Immediately after leaving the prism,
put for accuracy telescope. The Professor
then went on TO show how easily spectroscope might
be made by any person Of ordinary ability after which
he said To show that have not caricatured the
epectroscope, my assistant, Mr. Dudley, will throw on
the screen picture Of the first specroscope used by
Prof Bunsen. 1t consisted OF wooden box with two
telescopes, one of which had slit IN the
eye-pece fastened in 1t. This, said the
sneaker As the instrument which the beginning OF
spectrum analysis. For chemical analysis more com
picated apparatus is used. DubOsc's speetroseope,
which consists OF three telescopes mounted stand,
and which contains only single prism, was then ex-
planned The third telescope has scale illuminated by
means Of a placed adjacent TO it, and by 1t may
be shown position OF the various lines IN the spec
frum For physical investigation still more complicated
forms OF instrument employed 1t is necessary In
rome cases increase the dispersive power vastly To
do his more prsms added KirchhoTs spectroscope
has four prisms and two telescopes In it the position
of the lines measured by the angular displacement OF
tba telescope or the arc over which the telescope must
be moved in order TO them. The spectroscope at
Kew England has less than nine prisms arranged in
circle Pictures these instruments were then thrown
on the and explained.
cAUsEs OF coLoRED LIGHT.
Tie question comes up, continued the speaker,
what kind Of spectra and how many are therei The
xaue of the instrument manifesty depends upon the
number OF spectra which to be II there only
one specra the instrument is OF very little use Let us
nee AS we sort out various materials by means OF
various media-shot for example by means of sieves
&cso we may sort out each OF cOlors in the spectrum
White light s white because It eoetalns all OF them
and cOmesttO from solids liquids heated I'LL they
substance when IL first became luminous red the
heat continued orange light added TO the red then
light II was white hot" Tue light from II was white
because it contained all the colors.
done with condensed gases. In addition 20 white
light also know OF various colored lights Why are
part OF themi Light have color for either OF two
First the color may be the resdne after the
Ond the color may be original and the light mOnochro-
efler maxim viii ife acl iaC