The evening times. [volume] (Grand Forks, N.D.) 1906-1914, 1906-10-08
THE LARGEST TELESCOPE.
Details Of Harvard's New Flve.Foot
Reflector That Took Two Years
TO Pint In Place.

to Put In Place.
The biggest telescope in the worl,
is the Common telescope. s full feet IL
diameter and 20 inches wider than TIL,
Yerkes. 1t was constructed about II
years ago by DR.. A. A. Common, o vel
known astronomer of England. who
wanted 1t for research work that hi
was doing. He died soon afterwar
and his fine telescope became idle
Two years ago 1t was purchased by
the Harvard College Observatory
which proceeded at once to mount /,
on the observatory grounds at Cam.
bridge.
The first sod was turned September
-. 1904. Since then the work has gone
on steadily. but 1t has been necessarily
rather slow, for mounting a telescope
is not like building a house. More
over. this telescope has very unus-
ual kind of mounting. Most large tele-
scopes are supported by pedestal or
foundation pier of cast iron, cement,
or masonry firmly built upon the
ground, but this telescope is held in
position by Il big hollow cylinder that
floats in Il tank of water.
In the first place a deep excavation
was made on the spot where the tele-
scope was to stand and tank was
constructed with thick walls of solid
concrete Is feet deep at the farther
end and 81 feet long. the bottom of
which slopes upward from the end at
an angle of IS degrees to the surface
of the ground.
In this tank the water tight steel
float or cylinder. which is is feet long
and Z feet inches in diameter, is bal
lasted at the same angle as the bottom
of the tank. the buoyancy of the water
supporting its weight, and delicate piv-
OTIS at each end serving to steady it in
position. Above this, and securely
fastened to it by strong iron fork and
bolts. is the great tube of the telescope.
The tube is not circular, as one
would suppose, but rectangular. Nor
has it solid walls. The upper part of
the tube for a distance of about Is feet
is kind of skeleton, constructed of
angle iron. which is now covered with
thick canvas, and has an inside meas
urement six feet square. The lower
end. which supports the mirror and is
bolted to the iron fork just mentioned.
is a hollow cube with sides six feet in
length that are made of steel plate.
The whole structure weighs num-
Der of thousands of pounds, but 1t is
so delicately poised that it appears to
have no weight at all. So strong are
the bolts and pivots that it can be
moved in any direction, up, down, or
sidewise. without the slightest Jar or
slip. The telescopes in most observa-
tories are handled by clockwork that
runs by a system of weights, but the
Common telescope is to be controlled
entirely by electricity.
Not bit of machinery is to be seen,
says the Boston Herald. The motors
are far away in the power house. In
the observing ROOM there is an cleo
trio switchboard on which are num-
Der of small switches and clutches"
that are connected by wire with the
telescope outside and which receive
the electric current by other wires
from the main power above at the top
of the hillside. The switchboard also
has little dials on it that tell always
just where the telescope is pointing,
so that it is not at all necessary to look
out to see.
The observing room is in a small
building built for the purpose. 1t is
comfortable room on the second
floor, with desk for the observer In
front of the wall next to the telescope,
and another nearby with the switch
board for the recorder, as the man is
called who moves and controls the
telescope while the observer is at
work.
People are apt to think of an astron-
omer as perched on a ladderlike fight
of steps and shivering in big lonely
dome on an icy winter night, vet gaz-
ing up eagerly through a ponderous
tube that will hardly move in response
to his numbed fingers. Here, while sit
ting comfortably in a warm room, by
merely looking down an ordinary ap-
pearing little tube, the observer may
see all the wonders of the sky pass
mirrOred before him, while the re-
corder, without single effort beyond
the touch of button or the moving of
switch here or there, to reach any
part of the starry sphere from horizon
to horizon as the observer directs
1t may sound rather odd to speak of
looking down a tube at star. This
requires some explanation. There are
two kinds Of telescopes, rejecting and
refracting. The rejecting telescope
has a mirror of glass covered with a
thin coat of silver, and shows the star
In the same way as the mirror over
your dressing table shows your image
and the room behind you, by throwing
back the light that falls upon it. The
refracting telescope has a lens made
of two or more discs of clear glass
that are set in the tube at the upper
end, and through them the light rays
from the star pass down the tube to
the eye of the observer just as though
he were looking through big magni-
flying glass.
The Common telescope is reflector,
and its great mirror, five feet in dame
ter, is placed at the lower end of the
tube, SO that the light from any star
that is to be examined reaches it by
passing down the length of the tube.
Then other smaller mirrors placed
along the tube above reflect this light
back again up the tube to the "eye-
piece" or smaller tube, which passes
through the wall of the observing room
to the observer. The end of this eye
piece through which the observer looks
Is closed by powerful magnifying
lens, SO that the image of the star,
which appears as a very small point
on the mirror, is a little enlarged.
This great telescope is intended
chiefly for photometric work, that Is,
measuring the light Of the stars. Pro-
lessor Edward c. Pickering. who is the
director of Harvard College Observa-
tory, has spent good many years in
this work, and he intends to devote the
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