The Savannah morning news. (Savannah, Ga.) 1900-current, 1902-04-20

star. The eye can not detect It, but the
spt ctroscope does. The astronomer al
lows the light of the star to come
through a slit and be broken up by
the instrument. He selects a single lire
of the spectrum of the star, chooses a
guide line beside it and watches Il. If
the star is approaching the light
waves will be shortened, and the light
will become slightly nearer the violet.
If it is receding the waves will be
longer and the light will approach the
red.
Red is slow pitch" in light, and blue
is high pitch" AS the star swings
about the curve at this end of it's or
bit the light gradually returns to nor
NAL, because the star, while moving
just as fast, is not approaching us as
much. AS the star turns back the line
goes the other side the normal. BY con-
tinual observation the astronomer finds
how fast and how far the star goes
each way and how often it does so. In
the case of some stars he discovers
that what appears to be one is really
two, which is shown by the fact that
a line will divide into two and one
part move up and down the spectrum
at the same time. Such stars are
known as spectroscopic doubles.
With another bit of apparatus the as
measures the neat the SUITS
send us. Some night in winter when
you are out of doors hold your hands
up and let Arcturus warm them. You
may not feel the heat, yet Arcturus
sends us most heat of all the stars. AS
tronomers say it is the hottest" 1t
gives us as much heat as a tallow dip
six miles away, would do. You can not
feel that, with your thick skin, but the
radiometer detects it and even less
with ease. For instance, this instru-
ment has been known to detect and
measure the heat emanating from a
mans face 1000 feet away. And the
man was an Oberlin professor in an
ordinary state of placidity.
With such instruments as that to use
the astronomer does not want to be
kept down longer to watching the stars
through a revolving telescope. He
wants to be able to mount his ap-
paratus on brick or stone piers. solid
ly, and to have the best and biggest
apparatus he can get, so he can make
his measurements with the greatest
accuracy. He doesn't want this APP
paratus to be moved and swung at
the end of a siX-ton tube mounted on
a pivot. He wants it where he can
encase it and keep it at even temper
ature, as he cannot do in the old way
And he wants to be able to switch
the star image from one instrument to
another.
So he has come to the horizontal
fixed telescope. There have been many
small, experimental telescopes of this
character built. There was a large one
at the Paris Exposition of 1900 but it
was probably never finished, for no
astronomer got the benefit of it. In
that same year the University of Chi
cago astronomers having occasion to
observe an eclipse of the sun in North
Carolina, built one. The eclipse was
to be total. The astronomers wanted
photographs made with long focus and
showing details. 1t would have been
manifestly too expensive for considera-
ton to build massive foundations and
erect an enormous telescope and dome
down there for that occasion. The
eclipse would not be total at Lake
Geneva, Wis, so they built in North
Carolina a long wooden shed light
tight, horizontal, with a dark room at
right angles at one end of it, The
shed was 615 feet long-the exact focal
length of the 6-inch lens they proposed
to use A coelostat. or clock motor,
carrying a plane mirror was set up in
front of the shed, and reflected the i'm
age of the eclipsed sun through the lens
down the shed to the plate.
Remarkable EIipse PhOIORrn.
1t was necessary--or desirable-to
make several exposures. The total
phase lasted 81 seconds. So a track
was built IN the focal plane, and a
ball bearing carriage set on Il. and on
this seven plates were put. Then the
workers. who stood IN the dark room
behind this line Of plates, had but TO