The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1877-08-23
From the Scientific American.
Some New Inventions ScccSSary Tor
Eusure ASSrGuEu cal observations.


Some New Inventions Nccessary for
Future Astronomical observations.
Persons who have never seen Il frSt-class
astronomical observatory, nor read de-
tailed description OF the same, can have no
idea OF the peculiar difficulties which are
encountered and have to be. overcome at
any cost One OF these is that when telc-
scope ma9ui1its the size OF any object 1t
maguilcs also its motion, whether real or
apparent, in the same proportion. Any
one who ever looked through Spy-glaSs
knows that it must be held perfectly still.
and that any motion communicated to the
same causes an apparent motion OF the OBJ
icct observed, and that this motion is larger
in proportion to the power OF the glass. SO
in an opera-g glass, which never magnitcs
beyond 3, !, or ) dameterS-the motion
OF the hand in which it is held is OF not
much consequence; but when using long
marine Spy-glaSs it is necessary to hold it
quite still, and some improvi>ed support is
necessary, among which one OF the most
convenient is the shoulder OF person
standing in front OF the observer. For
large spy-glaSses or small telescopes foot
niece is necessary, and this must have more
stability in proportion to the power Of the
glass, as the least tremulouS motion in the
instrument causes q strong vibration OF the
object seen--so much, indeed. that observa-
tions are often intcriered with from this
cause.
This is the reason that it has become no
longer customary to establish observations
on the top of buildings, as was done in
olden times, but on the ground floor. SO
the old observatory OF the University Of
Leydcn, situated on the top OF high build.
ing, possessed large Ncwtoniau telescope
constructed nearly a century ago b. maker
who had attained great reputation in this
line but the instrument was rendered per-
fectlr useless by the continued vibratory
motion, either by wind, passing csr-
riages, moving OF persons in the build
ing, etc. The objects observed were almost
always seen In a condition as il tossed
by waves. Some two years ago this tele-
scope WAS still in existence, and shown "a
curiosity, when the writer OF this article
could not help but admire the useless inge-
n,litr with which it was mounted, and
which for an instrument OF that power was
entirely out Of place.
By the general revival OF astronomical
science, whicn became very active ut that
period, it was superseded bv q modern re-
tractor, mounted equatorially on solid
base placed ut u lesser height.
And here we must explain what is meant
bv equatorial mounting. The apparent mo-
ton OF the heavenly bodies, caused by the
carth's rotation around its axis, and which
increases along the celestial equator, which
is the principal region for observation, to
about Il quarter OF a degree for every minute
of time, is OF course magnitied in proportion
to the power OF the instrument; so for a tel
cscope magniiying say 120 diameters, it will
be l2O times as much, or 80 degrees for
minute, or half degree for Il second OF time.
1t is evident that in such q case no object
would remain in the field OF the telescope
long enough to be seen or studied, but stars
and planets would move through the field at
too rapid rate. The equatorial mounting
thus is intended TO cause the telescope to
follow that motion, and is accomplished in
this way: in place of mounting the joints,
by which the free motion Of the instrument
Is obtained, to vertical, solid pillar, they
are attached to an axis placed parallel to
the earth's axis, and this axis is rotated by
clockwork at the rate OF once in "a hours,
in an opposite direction to that in which
the earth is revolving, so that these two
movements neutralize one another; and the
telescope, il left to itself, is rendered i'm
movable in space, except following the
earth's yearly orbit, which, however, does
not influence the direction OF the instru-
mcnt to any perceptible degree.
The apparent motion OF the sun is slower
than that Of the fixed stars, for one day per
year, or nearly one degree for every "a
hours. The apparent motion OF the moon
is again slower to an amount OF nearly
thirteen degrees for every 2+ hours. The
clockwork regulating the rotation OF the
telescope axis has to be set in accordance
to the intention to use the telescope to OBJ
serve the liked stars, sun, or moon, and this
movement must be more minutely regll-
lated in proportion to the power OF the in
strumcnt.
Lately great pressure has been brought
TO bear on those having the power or means
Of managing or founding astronomical OBJ
so as to induce them to have
large, powerful telescopes constructed.
telescopes have been spoken
Of, but the difficulty OF their mounting and
the absolute necessity OF regulating their
proper motion to follow the objects observed
appears not to have been thought OF, while it
is one OF the most important mechanical
problems with which the utility OF such in
struments will stand or fall
Suppose telescope could be constructed
which would bring the surface OF the planet
Jupiter to within an apparent distance OF
ten miles. Then not only the motion Of the
earth herself, but also that OF the planet in
his yearly orbit, and the immense velocity
of rotation around his axis in ten hours,
would have to be compensated for by the
clockwork attached to the telescope, as
without it the objects would fy across
the field with the velocity OF n railroad
train. To realize the truth OF this asser.
ton we have only to consider that the cir
cumference OF the planet amounts to
quarter OF million miles, so that every
point OF its equator moves that distance in
1 little less than ten hours, equivalent to a
velocity OF about $4,000 miles per hour.
Seeing objects moving with such velocity
1t distance Of ten miles is equal to seeing
3biee4s move with 1-500th part of that
velocity mt distance of 1-500th part OF ten
miles, which corresponds to observing
/ velocity OF so miles per hour at
distance OF "a feet. Looking, therefore,
with telescope bringing The SURFACE OF
Jupiter to nm apparent distance OF ten
niles would be equivalent to looking at
/ distance OF only 81 feet at railroad
rain moving at q velocity OF so per hour.
)f course nothing could be distinguished.
rhe problem is therefore not alone to make |
he lenses and the tube gigantic telescope,
mt an enr.liy imDOrtanf problam IA the