Evening star. [volume] (Washington, D.C.) 1854-1972, 1893-12-14
TO PHOTOGRAPH THE STARS.
The Bruce Telescope VIII Make Many
Additions to the Map Of the Heavens.

The Bruce Telescope VIII Make Many
Additions to the Map of the Heavens.
From the Boston Evening Transcript.
The Bruce Photographic telescope. which
has so long been in process of construction
at Alvan Clark & Sons, Cambridgeport will
soon be set up at the Cambridge Observa-
tory, and will probably be in operation in
the course of a month. Its completion will
mark new epoch in this branch of SCI
ence, as 1t Is the largest and 1t is thought
to be the most powerful instrument of its
kind which has yet been set up. The base
and operating machinery are already in
place at Cambridge, and the tube and
lenses, although still at Clarks' works, are
practically completed. 1t Is expected that
with this instrument stars can be photo
graphed which have never been seen
through the most powerful visual tele-
scopes.
The instrument differs from the ordinary
large telescope in the construction of its OBJ
Ject lens The Photographic telescopes COM
monty in use differ but little from an ordi-
nary visual telescope with an arrangement
for the reception of a Photographic plate.
This instrument. however. in place of the
ordinary lens, composed Of two pieces of
glass, has compound lens made of four
pieces, which resembles the portrait lens
used by photographers. The objective Is of
"a inches aperture and the focal length Of
the tube is IL feet.
Two instruments constructed on this plan
are already in the possession of the Cam
Dridge observatory, one at Cambridge and
the other In Peru. and have given the
greatest satisfaction. They are both of
eight-irch objective, and with them 1t has
been found possible to photograph stars
that were not visible through a 15-inch
visual telescope. 1t will, therefore. be seen
that II the instrument now being construct
ed should be powerful III the same ratio It
will exceed in power a 45-inch telescope of
the ordinary kind. AS the largest one at
present in use is the Lick telescope, which
Is OF 36-inch objective, and the largest any,
where near completion is the great instru-
ment for the University of Chicago. with a
4O-inch lens, 1t Is fair to suppose that the
Bruce instrument will photograph stars
which can be seen through neither of these
The instrument is superior to the ordinary
one, not only In power, but in the expanse
or sky which can be taken upon a single
plate. The ordinary telescope will cover
only about four degrees at a single ex-
posture, and as there are 10000 degrees in
the whole expanse of the heavens, 10000
plates would be necessary for a complete
record of their whole area. The new tele-
scope will cover six times the area, and
will take the whole heavens in 600 photo
graphs. These photographs. when taken,
Will not only show many hitherto unknown
stars, but will be a valuable and indis-
putaole record of the state of the heavens
at the time they were taken. The whole
series could be completed in about a years
time, but Ii Will probably be longer than
that before it is finished, as the telescope
Will be used for other purposes in the mean
time.
The new telescope Is the gift of Miss c
w. Bruce of New York. 1t will remain at
Cambridge until its capabilities have been
thoroughly tested, which will probably be
IN two or three years, and then will be
shipped to its ultimate destination in Peru.
Here 1t will be set up on a hill near Are
quipa; where the South American branch Of