The morning news. [volume] (Savannah, Ga.) 1887-1900, 1900-05-19

The Cape of Good Hope Instrument.
Its Powerful CIockwork - Paris
Exposition Glass The worlds
Greatest TelescOpe-AstrOnOm
Predictions for April, 1900.
Harold Jacob In Boston Transcript.
There are many interesting practical
things about an astronomical observatory
with which the public seldom has an OPP
portunity TO become acquainted. Among
these perhaps the details connected with
setting up a great telescope take first
rank. The writer happened 10 be present
at the Cape of Good Hope Observatory
when the Photographic equatorial tele-
scope was being mounted, and the opera
tiQn of putting it in position may be TAX
en- as typical of similar processes else
where.
10 the first place, it is necessary to ex-
plain what is meant by an requatoriar'
telescope One of the chief difficulties in
making ordinary observations arises from
the rising and setting of the stars. They
are all apparently moving across the face
of the sky, usually climbing up from the
eastern horizon, only to go down again
and set in the west. If. therefore, we
wish to scruunize any given object for a
considerable time we must move the tele-
scope continuously so as TO keep pace with
the motion of the heavens. For this pur-
pose the tube must be attached to axles,
so that 1t can be turned easily in any di-
rectlon. The equatorial mounting is a de-
vice that permits the telescope to be thus
aimed al any part of the sky, and at the
same time facilitates greatly the opera
ton of keeping it pointed correctly after
a star has once been brought into the field
of view.
To understand the equatorial mounting
1t is necessary to remember that the ris-
ing and setting motions of the heavenly
bodies are apparent ones only, and due In
reality to the turning of the earth on it's
Own axis AS the earth goes around it
carries observer, telescope and observa-
tory past the stars fixed upon the distant
sky, Consequently to keep a telescope
pointed continuously at a given star, ii is
merely necessary 10 rotate ii steadily
backward upon a suitable axis just fast
enough TO neutralize exactly the turning
of our earth
BY a suitable axis for this purpose we
mean one so mounted as to be exactly
parallel TO the earth's own axis of rotat ton
A little reflection shows how simply such
an arrangement will work All the heav-
emily bodies may lie regarded, for practical
purposes, as excessively remote in COM
The entire planet shriaks into absolute
insigniticance when compared with The
distances of the nearest objects brought
under observation by astronomers. 1t fol-
lows that If we have our telescope attach
ed TO such a rotation-axis as we have de-
scribed, 1t Will be just the same for pur-
poses of observation as though the tele-
scopes axis were not only parallel 10 the
e2rth's axle. but actually coincident with
it, The two axes may be separated by a
distance equal to that between the earth 5
surface and its center; but as we have
said, this distance is insignificant so far as
our present object is concerned.
There is another way TO arrive at the
same result. We know that the stars in
rising and setting all seem to revo,ve about
the pole star, which itself seems 10 remain
immovable. Consequently, if we mount
our telescope so that II con turn abo [
an axis pointing at the pole, he shall be
able TO neutralZe the rotation of the sta 5
by simply turning the telescope about tn :
axis at the proper speed and in the right di
rectiOn. Astronomical considerations tea N
us that an axis thus pointing at the pole
will be parallel 10 the earth's own axis.
Thus was arrive at the same fundamental
principle for mounting an astronomical
telescope, from whichever point of view
We consider the subject.
Every large telescope is provided with
Sucn an AXIS OF TOtAllOns ana Tor the rea-
son stated 1t is called the polar axis -
The telescope itself is then called an
Equatorial" The advantage of this
method of mounting is very evident. Since
we can follow the stars motions by turn
ing the telescope about one axis only, il
becomes a very simple matter TO accom-
plsh this turning automatically by mean
of clockwOrk.
The following" of a star being thus
provided for by the device of polar
axis, il is, or course, also necessary &c
supply some other motion so as to enable
Us to aim the tube at any point in the
heavens For 1t is obvious that If it were
rigidy attached to the polar axis we could
Ind ed follow any star that happened tC
be in the field of view, bat we could MOI
change this field of view, at will sc
as 10 observe other stars or planets II
accomplish this the telescope is attached
10 the polar axis by means of a pivot. BY
turning the telescope around its polar
axis and also on this pivot, we can fine
any object in the heavens and once found
we can leave TO the polar axis and its au
tomato clockwork the task Of keeping
that object before the Observers eye
In setting up che Cape of Good Hope
instrument the astronomers were Obliged
to DO large part of the work Of adjust.
ment personally. Far away from Euro.
pean Observation-Disclosures, the parts of tho
mounting and telescope mad 10 be "assem-
bled," or put together, by the astronomer.
OF the Cape observatory. A heavy pier OF
BRICK and masonry had been prepared il
al, ance. Upon this was placed massive
on tase, intended TO support the super.
structure Of polar axis and telescope Thi.
base rested on three points. one of which
could be screwed In and out. so as TO til
The WI ole affair little forward or back
ward BY means OF this screw we effect
ina "A III AZ ont If he
90 exact parallelism with that OF IN,
earth. Other screws were provided with
VII ch the base could be twisted a litti,
Horizontally either TO the right or left
Once set up in a position almost correct
II was easy 10 perfect the adjustment b,
the aid OF these screws.
Afterward the tube and lenses were pu
IN place. and the clock properly attached
INSIDE the big cast-iron base. This heav,
eaockwork looked more like piece O