Evening star., 1894-03-24

constantly darkened by exterior shutters
anu interior screens. IN order 20 exclude
eAtraheous sunlight and neatand the whole
DuilGlng is closed tightly 50 as TO keen out
uraTS, while the air within is maintained
at uniform dry artificial temperature of
between 100 and 10 degrees Fahr.u beit
TO prevent the moisture from afectin- the
SAT- pT'sms used in the spectroscooe.
In one of the two apartments is ricged
up sensitive instrument of Prof. Lang
leys invention, called a bolometer. and in
the adjoining room is a galvan norn eter Tlac-
ed IN electrical connection with the bolon-
eter. The bolometer is a marvellous crea-
tlon' IL serves as lmiauti"e and super
sensitive thermometer, and consists of a
minute strip of metal l-500 of an inch wide
and 10000 of an inch thick; in appearance
resembling a tiny hair. 1t iss indeed so
sensitive itself, and its mountiags are so
uellcate, that 1t has to be installed on a
stone foundation laid deep in The ground,
lest IT be disturbed and thrown into false
vibration by the passage of wagons or car
f1ages, or the footballs of occasional pedes-
trians in the park outside, and even by the
movements of persons inside. Through this
frail thread of metal a current of electric
lty is continually kept flowing. Whenever
the spectrum, visible or otherwise. is thrown
upon ii, the thread is warmed and the cleo
trlc current is decreased by an amount cor
responding to the intensity of the effect
received. Other novel instruments, special
ly mounted and constructed to connect
with the galVanometar, automatically re
cord the slightest change in the current.
SO delicate are these Instruments that
variation Of temperature to The extent of
one-millionth of a degree is readily de-
tected and even measured.
The Reflector.
Outside the building is a round reflector
of over a foot in diameter, made of perfect
glass ground fat a frame holdiag The re-
hector is mounted on a carriage connected
with an ingeniously contrived machine, so
adjusted as to keep the reflector moving
gradually with the movement OF the sun. A
ray of sunlight reflected from This glass,
passing through an aperture in the sky
light at the roof of the observatory, is re-
fracted through prism of salt as clear as
the finest glass and made to fail upon the
sensitive bolometer. When a dark (and
cold line in the spectrum is upon the DC-
lometer the instrument at onSe feels the
change of temperature and experiences a
chill. The observer, however, could not de-
tect this If II were not for She connection
with the galvanometer and its fairy-iihe
magnetic needle. This needle IS only one
sixteenth of an inch long, ana is detected
in response to the movements of the bOl1In-
eter But even its variations could not edsI-
ly be observed directly, and 50 a device rs
attached 10 il by which the slightest move
ment is detected at once. Despite the
smallness of the needle, ii has an infinitcs-
imal mirror on its end scarcely larger than
the point of a pin. Additional rays % light
are trained by other felleclOrS 50 as % Kan
upon. this mirror. In turn the ray IS se-
fiected so al to make a little point or dot or
light on a screen few feet away But thai
spot is sufficient. If the needle merely
trembles, the angular movement or the re-
1ected raw is so great as TO make the spoi
Of light move perceptibly on the screen. al
II the needle is DETECTED considerably the
spot will make quite a journey across the
screen, thus aftording a means of observing
and registering the readings or the bolom-
This record can be made permanent by
substituting a sensitized Photographic plate
for the screen.
The Science of Astro-Physics.
The beginning of this new science Of as
tro-physics dates back almost to the dis
covery of the spectroscope-that familiar
optical instrument for examining the lines
of the spectrum with view to determin-
ing from their position the composition of
the substance from which they emanate-
and the spectroscope has been largely en-
ployed in the researches thus far conduct
ed. 1t is a wel,-known fact, though, that
of the heat which the sun sends down to
the earth the ordinary sceptroscope can
recognize only one-fourth-the other three
fourths being in a form which the ordinary
spectroScope cannot see or analyze, lying
II visible and beyond the ''red-end' of the
spectrum where also neither the eye nor
the direct processes of photography can eX-
anime it. For years this invisible portion
Of the solar spectrum has been known to
exist, and yet nobody was able to exhibit
it. But were the range OF human vision
vastly extended, so as to enable us to re-
ceive optical impressions corresponding in
character to the kind OF energy present in
this 'infra-red" region. We could see in
that region phenomena OF precisely the
same sort as We now note in the spectral
region TO which we are confined by the re-
s:ricted powers of the human eye. 1t is to
this hidden field, therefore. this great un-
known dominion beyond the limit Of the
reds" that the modern astro-physicist now
directs his attention.
BY special method invented by Prof
Langley systematic explorations have been
made Of this unknown region. and. gratify-
ing TO relate, complete map of IL has lust
been produced. With the aid Of special ap-
paratus constructed by him the lines of the
invisible spectrum are shown almost as
clearly the lines of the visible The
chart reproduced herewith OF one of the
rock-salt spectra of the invisible spectrum
is a sample of the valuable results already
attained at the observatory within the last
two years by the new spectre bolographc''
process. In il the visible solar spectrum,
as known and investigated by Sir Isaac
Newton, is represented to its length by
the blank space on the left. from to 5,
while the lines mapped out to the right,
from to 6O-nearly thirteen times the ex-
tent of those known to Newton-are among
those newly discovered. The lines indicat ted
were reduced from ''bolographs" and per-
manently registered by means of photog-
raphy.
This invisible portion Of the spectrum, Il
Is found, like the visible, is marked by mar
row bands or lines. but almost entirely de-
void of what physicists call energy" The
world owes TO the study of the 'Fraunhofer
lines of the visible spectrum nearly all
those recent advances which have given US
definite information regarding the consti-
tuition and composition of the heavenly
bodies. and which have been Of SO great
advantage in the study of the meteorologi-
cal and atmospheric phenomena of the
earth. The study of the lines in the invisi-
BILE spectrum by the new method is be-
lieved TO be of equal. or even greater prac-
teal Importance.
Frof. Lan2ley's Success.
Professor Langley has succeeded in bring
ing his original bolographic apparatus to a
greater degree of perfection and effective
ness than has ever been secured before
elsewhere, and il is subject of pride with
the Smithsonian people that our own mod
est little astro-physical observatory, the only
one Uncle Sam possesses has, in the two
years of its existence, enlarged the world s
knowledge of the solar spectrum-particu-
larly that part discovered since the time
of Newton, by far the most important in
its bearings upon the questions of climate
and agriculture-to a greater extent than
all other astro-ph ysical obSerVatorie in the
world combined. And the significance Of
this advancement will be all the more ap-
pl eciated when IL is borne I'm mind that the
competing institutions in Europe are very
elaborate and expensive establishments
heavily endowed and operated by savants
of wide distinction. Most of the leading
European governments have within the