The record-union., 1892-05-02
SPECTRO-PHOTOGRAPHY.
The Progress Made in Physical
Astronomy.
The Wonders of the Heavens Disclosed
Discoveries Made Which Were
Not Dreamed of Few Years Ago
Latest News From the Regions of
Space.

For some years past physical astronomy
has made considerable progress. 1t has
been within a short time enriched by
method of exploring the depths of space
which is truly admirable. Spectre pho
Biography provides a means of discovering
stars which cannot be seen, and which
doubtless never will be seen, of measur-
ing their speed of movement, their mass
and other things. 1t is an exploration of
the invisible. The method is one which
excites astonishment. No telescope can
reach so far into space. Moreover, by
telescope the distance from the earth of
stars very far away cannot be measured,
and it is impossible to say at any given
moment whether such stars are moving
toward or away from the earth. By
spectro-photograp not only can their
movements be determined, but there
have been discovered stars the existence
of which quite recently was not even
suspected.
Every one knows what is meant by the
spectrum of light. The luminous rays
which have passed through glass prism
are refracted and expand into band or
ribbon, which exhibits all the colors of the
ralnbow-violet, indigo, blue, green, yell
low, red. This colored ribbon is crossed
transversely by numerous lines. In 1862
Messrs. kirchoff and Bunsen, profiting
by the numerous researches of their pre-
decessors, pointed out, under the name of
spectral analysis" method which has
proved extraordinarily fecund in great
results. 1t marks, in fact, new era in
the evolution of physical astronomy.
Kirchoff and Bunsen demonstrated
that, by the aid of the transverse lines of
of the source of light could be shown.
Certain lines must be produced by GER
tain substances. BY examining the
spectrum it became easy to tell what was
the luminous body of which that spec
trum appeared. The characteristic lines
of each substance are,written like a sigma
ture upon the spectrum. In this way we
can know that the sun contains the same
materials as the earth. We can learn that
everywhere the stars are composed Of
substances known to US. The unity of
the composition of the earth and stars has
thus been determined, at least for the re-
gions within our horizon of sight Spec
trail analysis, however, has considerably
enlarged our horizon.
photography is the child of
spectral analysis, but is founded on an
other discovery originally made by the
physicist Dopper of Salzburg in 1912. In
observing certain stars, it was observed
that the transverse lines In the spectrum
of these stars were not always straight,
put were bent in the middle of the spect-
rum, sometimes in one direction, some
times in the other. How can this differ
ence in the lines be explained? When
you are travelling on railway you often
hear the sharp whistle of an engine
which crosses the train on which you are
The whistle becomes more strident as the
other train approaches and less so as you
are separated from that train. 1t
was shown by Mr.. FiZeau that
in this case the waves of sound
are crowded closer together when the
two trains are approaching each other;
greater number of these waves strike the
ear at the same moment, and the greater
the number of vibrations perceived by
the ear the more piercing is the note.
The same phenomena take place in
waves of light. If the luminous focus is
approaching us, the waves of light crowd
together, and each of them is shortened;
they increase in length if the focus is GO
ing away from us. Now, the position of
the transverse lines in the spectrum de-
pends precisely on the length of the
waves of light. Consequently, the dis
placement of transverse line on this
side or that of it's normal direction reveals
the fact that the body which sends its
light to US is in movement, and the diver
sion of part of the line enables us to
know the speed with which the
luminous source changes its place.
Then by tracing minutely the displace-
ment of a transverse line we can, in our
study, ascertain with what speed a star,
of which the movements in the direction
OF our visual ray, approaches or recedes
from the earth.
Now, nothing prevents the photograph
ing spectrum. So that we can after
wards at our leisure study on the photo
graph the successive displacements of the
lines of the spectrum. This was the ori-
gin of Spectro-photography
How, 1t Will be asked, can you know
that such or such a separation of the
spectral lines corresponds TO such or such
o speed of movement of the stars? By
calculation, ald, as corrective or guaran-
tee of that, by comparison with known
rates of movement in celestial bodies 1t
was the regretted Mr.. ThoIlon, of the OBJ
servatory of Nice, who made this verifi-
cation with most precision, by following
a well-detined point on the solar surface
The sun turns at rate of speed which is
well-known; and with it the luminous
point. on can then calculate the dis
placement of the lines of the solar spec
trum, and by comparing that displace-
ment with the known rate of speed of the
sun can tell what speed is indicated by
the displacement of spectral line Of any
celestial body.
For several years past this method has
been employed everywhere in the great
obServatorieS at Greenwich at Paris at
OtSudiIl, pul specially AT harvard Col
lege in the United States. Nowhere
have more surprising results been OBJ
tanned than at Harvard. There the Ia
bolS of MIR. Draper have been continued
by Edward Pickering, who photographs
regularly the spectrums of the stars.
The examination of the photographs is
1ntrusted TO women. Last year Miss
Maury, assigned to study the photo
graphs, perceived in examining that
of the star Zeta in the Great Bear,
that a certain line across the spectrum
OF that star periodically doubled in
width, then became simple, then doubled
again, and this every fifty-two days.
hat are we to conclude from this
Very probably that this star of the
Great Bear, which has always been con-
sldered single star, is double one,
and formed of two bright stars which
our instruments cannot separate.
With the star Beta, of the constellation
Aurlga, the doubling of the spectral line
at times is still more accentuated The
measures of separation of spectral lines
permit us to determine that Beta is, in
place OF one star, two, which complete
their erbit every four days. The speed of
movement is enormous-l50 miles a sec
ond, which corresponds 10 an orbit of
about $500, 900 miles. With these factors
can be calculated the total volume of the
two stars, which is two and half times
that of our sun. To see these two stars
separated, there would be need of a teIe-
scope with an object glass about thirty
eight yards in diameter
Consequently we find, away in the
depths OF space, at the distance of ninety
thousand million leagues, star of Auri-
ga, which we can barely distinguish. For
all astronomers, ii was but one star. The
new method reveals the truth. This star
is associated with another. The two stars
revolve one around the other with speed
i