The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1897-05-23

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as the case may be, receive impre ssions
Photographic room.
As the spectra OF terrestrial substances
are needed for com parison the upper Sec
ton OF the spectrograph is furnished with
a Geiss!er's tube, which can be instantly
put in place and the glow of incandescent
hydrogen and other gases be substituted
Tor the celestial CLEAN whose identical
track through the collimator and prisms
they are made to traverse. In the Illus
tratlon is shown the position of the eiec-
trio arc for procuring the spectrum OF
iron, and the electrical coils used are con-
veniently stored in large triangular
wooden case near by. This might be a
dangerous adjunct elsewhere, but scien-
titlc pursuits engender forethought and
wariness.
By slight adjustment of the photo
graphic-plate holder and momentary
screening OF the star spectrum that pre-
viously left its impress, the plate can re-
ceive celestial and terrestrial spectra
ranged one above the other for COMPARE
son. The lines of the latter will hold a
normal position, while those of the former
will be displaced to either side, if it be-
longs to some swift orb earthward bound
or else speeding directly from our vision.
The mystic handwriting on the wall In
Babylon, but for its tragic import could
not have awakened more thrilling interest
than does first experience in decipher-
ing the prismatic scroll; but habit is a
speedy eraser of emotion, and no lawyer
hp Of Loo IN lyf,lv
than a spectroscopist scans the faint rec
ord that has come from a:ar.
To counteract the faintn So of starlight
powerful microscope is used to inspect
the plates, and as displacements due to
motion in the line of sight are entirely in
dependent of distance they are nearly as
measurable with the aid of micrometer
wires as the more distinct sun and planet
lines. AS changes of temperature have a
tendency to alter the positions OF the lines
the spectograph. when in use at night, is
enshrouded in black velvet case, for a
reliable record of displacements Is the
chief aim of the carefully devised appar-
atus and of the tireless solicitude rs to ad
justment.
That expressive phrase, the star depths,
which contradicts the vaulted aspect OF
the sky, applies chiefly to the range of ar
tificially aided vision, though the ordinary
observer also fathoms more or less with
every glance. 1t is easily discerned that
Sirius shines with blush white light,
that Arcturus, now on the meridian at 10
P. NJ, has yellow tint, and that Antares
at the same hour STIMULATES from the
southeast wi tn fiery gleam
The use of the prism emphasizes these
tint of each really predomnates in its
spectrum. The dark lines crossing the re-
fracted beams differ in number, position
and aspect, though o few are identical in
all. AS these lines are clew to many of
the constituents of an incandescent body
the materials of distant star are not al
together unknown. Absorption lines of
hydrogen predominant in the spectrum of
Sirius and of all white stars, which are
accordingly classed as of the first or Sirian
type.
The spectra of yellow stars may be
briefly described as faint copies of an
aiyzed sunlight, and are known as OF the
second or solar type. These two classes
comprise very nearly the entire celestial
host but few hundred being as yet
known. The latter are subdivided into a
third and fourth type, While there is
marked difference in the typical speci-
mems of each class, as shown in the illus
tration, there have been found, however
few intermediate spectra that suggest
gradual development of stellar conditions.
1t is not known as yet that the theoretic
age of star-itse!f very unsettled ques-
tion-has any bearing on its proper motion,