Kenosha telegraph. [volume] (Kenosha, Wis.) 1850-1854, 1850-10-11


globules to escape. Such was at length discov-
cred, and it is this which has deservedly stamp
ed Lord Rosse's name with celebrity reducing
as it does the casting OF specula to certainty.
The simplicity of the continuance causes it to APP
pear matter of no great wonder but like the
plan pursued by Columbus to make the egg
stand on end, it is easy only when it is known.
The continuance consisted in making the bottom
of the mould of layers of hoop iron, bound close
ly together, with the edges uppermost. BY this
means the iron conducted the heat away through
the bottom so as to cool the metal towards the
top, while the interstices between the hoops,
though close enough to prevent the metal from
running out, were sufficiently open to allow the
air to escape. At my visit, bad an 0pportnni-
ty of seeing this singular mould; it was large
dish of malleable iron, the layers OF which were
about half an inch thick and to all appearance
so closely welded, that the water could not filter
through them.
The first large speculum thus made in sin
gle piece was round plate OF metal three feet
in diameter, nine inches thick. and upwards OF a
ton in weight. On becoming solid, it was re-
moved, to be annealed, to brick oven, the mouth
Of which is level with the ground, at the dis
lance OF q few feet The oven was nearly red-hot
when the speculum was shut up within it, and
from this temperature it was allowed to become
gradually cool, when the annealing was compile
ted The time required for annealirg plate of
this large size is, believe, about three weeks
and yet, with all this attention, so brittle is the
metal, from sudden variations of temperature,
that warm hand laid upon it in cold night
will make il fly in pieces.
Following the mass to the next stage in its
progress, we find it placed, with the face upwards,
upon turning apparatus. Here it seemed mo-
wing round slowly, immersed partially in water,
in order to be kept cool, while grinding or rub
bing tool works on its surface. BY means of
this grinder with emery and water, and the ad-
justed rotative motions, the proper parabolic
curve, along with certain degree OF smoothness
is produced after which the surface is similarly
polished with resin, and some other substances.
The grinding is performed on the ground floor
OF a house, adjoining which is tower several
stories high On the top of this tower is erect
ed a mast, the summit of which is ninety feet
from the speculum on the grinding machine
To the top Of the mast the dal-plate of a watch
is fixed, forming small round object relieved a.
gainst the sky. When the workmen wish to
try the capacity of the speculum, it is cleared of
its grinder, trap-doors overhead are opened, the
figures on the dial-pate are reflected on the spec
ulum, and this reflection is seen at the regulated
focal distance by means of small eye-piece, in
other words temporary telescope is formed with
out a tube, and by this ingenious yet simple de-
vice, the spectrum is wrought TO that nice para
bollc figure which brings the incident rays to an
exact focus. OF the extreme accuracy required,
we may obtain some notion from a statement OF
Lord Rose, that an error of small fraction of
hairs breadth would destroy all hope of cor
rect action and DIR. Robinson mentions that
the smallest pressure during the process, would
be attended with the result Of changing a well
defined star into a blot or comet. The specu-
lum, nevertheless, was polished in the short
space Of six hours.
The spectrum, so fortunately completed, was
fixed or bedded onthree iron plates, which gave
it support, and then transferred to its appointed
situation in the tube. This, as | have already
noticed, is three feet in diameter and twenty-six
feet long. and attached to an apparatus on the
lawn, by which it can be brought to bear on any
point of the sky short way above the horizon.
The machinery for moving it round and raising
and depressing it, is simple and ingenious, and
notwithstanding its size, may be adjusted with
the greatest ease. Two step-ladders form part
of the apparatus, and by these we mount to gal
lery, which can be raised or lowered to any re-
quired height In order to procure an observa-
ton, the tube is first brought to bear on the star
or other object, and the gallery being raised, we
ascend to it by one of the ladders On reaching
tie gallery. which is small rallied platform sut-
fcient to hold several persons, we find ourselves
close to the telescope, near its upper extremity;
and here, on looking through small eye-piece
fixed to the tube, we at once recognise in the OBJ
liquply-placed mirror within the object of our
observation. The tube is OF wood, hooped with
iron, and the focal distance of the speCuum is
tWenty-seven feet. | was rather surprised to
find that the mouth of the tube remained perfect
" open-the natural idea arising in my mind
being that the rain and vapors would enter there
by, and iniure the spectrum at the lower eX-
tremty | was informed, however, that the tel
Escape is lowered in wet weather, and that the
spectrum is confined in case, the cover of
which Is withdrawn by an exterior action when
required A vessel of quicklime is also kept
constantly in the case, for the purpose of absorb
ing the moisture and acid vapors by which the
speculum might be furnished
The power of the telescope depends on the
glasses employed in the eye-piece This re-
quires little explanation. The rays collected
by the specuum are directed on the mirror at the
proper focal distance, and there reflected clearly,
or brought within telescope reach. A telescope
must be employed to magnify the image, or draw
it OUT and accordingly, a small telescope like a
pocket preparedness, technically an eye-piece,
is used for this purpose But this eye-piece re-
quires to be used with discretion: its glasses
must be shifted according to circumstances
Unless the atmosphere be exceedingly clear and
dry, powerful telescope will magnify its parti-
cles, and these will seemingly form haze inter
ceptive of lucid observation. Different densl
ties, from contending strea ans OF warm and cold
air, will have a similar result; and If the atmos.
phere be excessively cold, as IN Russian Win
ter, floating spicule of ice invisible to the naked
eye, will be magnitied so as equally to INTERRUPT
perfect astronomical observation. Such coffin
gencies present serious drawbacks to the in
crease of power in telescopes; and In the instru
ment we have been describing, they are attempt
ed to be overcome by employing various eye-pie
ces, whose magnifyng powers range from Isl
to 1000.
The performances Of this magnificent TWEEN
ty.six feet telescope were found to be far be-
yond those of any previously constructed instru
ment. Certain patches of light or nebalous nat
ter in the heavens were resolved into clusters o
separate stars; stars hitherto seen but dlmly
appeared round and well defined; and on tht
surface of the moon, valleys, mouhtain-tops, ant
craters of volcanoes were plainly visible. Graf
living as were these results, Lord Rosse con
sidered that something still grander could be a
! chieved and before the twenty-slx feet tele
| seope was well finished, he projected the gigan