Year: 1866

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size, and when we come to the size OF


about foot in diameter there are very


few glasses in the world exceeding it
which are quite perfect. A very com
mon adjunct of that large telescope is
a cap made to fit the object glass with
an eccentric aperture, which is turned
round to the perfect part of tho glass,
shading the defective portion from the
rays which would interfere. with and


break up the object. This glass needs
no such cap, and in addition to its be-
ing the largest, it is also the most per-
feet and flawless in the world. 1t is so
mounted that it can be directed to any
point in the heavens by motions upon
two axes at right angles to each other,
one OF which is directed to the north
pole OF the heavens. BY means of
ciock-work of peculiar character it
can be made to follow the apparent
motion of star, so that, as the object
rises in the east, the telescope moves
with it. The mounting weighs about
three tons, but this great weight can
be moved by one man, and that with
ont much effort. The tower is so con-
structed as to be independent of any
casualty which may occur to the rest
of the building. The tripod upon which
the glass is placed stands upon a sol
id, self-sustaining pedestal, and the in
terror of the dome is perfectly fre-proof.
The dome is constructed to revolve
freely on balls with the motion of the
instrument, so that nothing but the
end of the telescope is exposed to the
atmosphere.


The uses to which this telescope
will be put may be defined to consist
in watching the heavenly phenomena
to observe the movements of plane
tary satellites, discover the conforma-
tions of the lunar surface, and the
changes which occur in the surface of
herself, and of the other bodies which
compose the solar system, to deter
mine relative positions of fixed stars,
and OF the planets, comets and aste-
roids, with regard to them, to dissect ont
the constitution of the fathomless neb.
ulous depths, and watch the changes
OF position of the members of those
wonderful star systems, which for
want of better understanding of their
character, are called binaries, tenaries,
and quarnaries, though for aught we
know each of those systems may be
composed OF much greater number
OF individual masses than those of
which the solar system consists. In
view OF its superior power and per-
lection we are warranted in anticipa-
ting great things from it, especially af
ter the other Instruments needed to
complete the full set of. observing APP
paratus shall have been supplied. In
deed, this glass has already effected
enough to immortalize the telescope.
1t is note worthy that the fact, long
suspected, that Sirius is one of bina-
ry system, was first discovered by
means of this glass, and that the fact
was calculated up by Professor SAT-
ford, before it was observed The dis
covery of this companion star of Sirius
is not, perhaps, as important an astron.
omical fact as the finding Of the planet
Neptune, yet it is of considerable in
terest, and there is strong parallel
between the two cases. The existence
of Neptune, so far as yet known, the
outermost member of our solar family.
was demonstrated by an astronomer
who weighed the masses of the then
known planets, and from a knowledge
Of the extent OF their perturbing power,
saw that some external force was at
work to produce certain Irregularities
in the course of the Georgian STAR
and calculated to within very small
amount of space the position of the un-
known wanderer, which was after
wards discovered in that very spot by
another astronomer in securing the
heavens. SO this companion star of
Sirius, whose existence was first de-
monstrated by Stafford, was discovered
10y means of the Clark glass. And
the coincidence that the man and the
glass are now both engaged for the
Chicago Observatory, may, perhaps,
be accepted as an augury of other as
Economical discoveries which shall
startle the scientific world.


We have not been able to obtain
from Mr. Clark the exact power of the
accessories to this wonderful glass,
but the following is near approxima.
tion to them The hour circle is about
eighteen inches in diameter and divi-
ded so as to read single seconds of
time the declination circle, at right
angles thereto, is about twenty-four
inches in diameter and divided to ev-
cry four seconds of arc. The astrono-
mical eye pieces, several in number,
possess magnifying power ranging
from about lao to 200 times, and the
micrometric eye pieces, used in meas
uring the exact value of small angles,
will magnify up to 1000. "The find
era small telescope with a larger
field, and axis parallel to the princi-
pal, will be about three feet six inches
long. Its use is to bring star the
more readily into the field of view of
the large telescope.