The Birmingham age-herald., 1913-05-04
Figure 2-The formations of the
spectrum of sunlight.

| "''''''...s................ ......"...s.o...uo"."
ter of the wonderful summer branch Of
| the Milky Way; indeed Scorpio may be
considered as the leader of this part of
the Milky Way, and when, as now, the
winter branch is sinking below the west
ern horizon, the summer branch begins
TO rise above the ground in the east.
TO the right of Scorpio are the two stars
of the Balances, and westward from those
there stretches the great Harvest constel-
laton OF the Virgin, whose bluishwhite
star, Spica, celebrated from the earliest
times as the Solitary or Defenseless One
is the brightest object in this part of the
heavens. This distant sun belongs to
remarkable class of stars, each mepber
of which, though 1t appears as a single
star even in the largest telescopes. is
known to be in revolution about darker,
invisible companion. The revelation of
these invisible stars about which many
of the bright suns are revolving is one of
the most surprising of the very modern
discoveries of astronomy.
How Invisible Stars Are Found
1t is we'll known to every one that when
q beam of white sunlight shines through
triangular prism it energies as a beau
tful band of light whose colors blend
from violet at one end to red at the other
| This is because the apparently simple
beam of white light is actually made up
different wave lengths. the waves known
to us as violet light being the shortest
While those which produce upon our eyes
the impression of a red color are the long
est. The shorter the light waves in the
ether are the more they will be bent out
of their course by their passage through
the prism. AS the wave lengths of violet
light are less than those of red light. the
colors will thus be separted from one an
other as illustrated in Figure 2.
If narrow slit be placed before the
prism SO that only very thin beam of
sunlight can shine through it, the color
| strip will at once become crossed by
multitude of fine, black lines whose posi-
| ton with reference to the direction of the
| narrow beam can be measured with great
accuracy. From many of the stars of
/ which Capella is an example, the color
| strip. or spectrum, is exactly like that
made by the light of our own SUM- from
| others we obtain a spectrum crossed by
| bright lines instead of by dark ones. But
| in either case the position of the lines de-
pends upon the lengths of the correspond
| ing light waves in the ether; that is, upon
| the number of light waves which pass
through the narrow slit in a given time
1t Is therefore evident that if we are
| approaching the source of light moro
waves will fall upon the prism in a given
| time than otherwise and that the wave
! lengths will thus become effectively
| shortened; consequently all the lines of
! the spectrum win become displaced to-
| ward the violet end. which is the region
| OF shorter wave lengths And If the dis
| tance between us and the source of light
| is increasing, the lines will be displaced
| toward the red. BY measuring the
amount Of this displacement we can even
| determine how many miles a second the
| star is approaching or drawing away
; from us.
| The spectrum of Spica is crossed by
! bright lines whose position shows US that
! hydrogen and heliam are especially prom
| ineDt in this star Al certain times these
are displaced toward the violet so far as
| 10 show that Spiea is then approa ching
| Us with speed OF Sc miles a second: two
| days later they are SO displaced toward
| the req tha4 we know that the star is
| then lecedtns from US with the same We
locltY After four days from the first
cate Ne find the star approaching us
again. and this alternate approach, ana
! recession continues with perfect regular-
itN indetiniteN. II. thus becomes evident
| That this bright siar is revolving about
: the common center of slsslt. Of itself