The Big Stone Gap post. [volume] (Big Stone Gap, Wise County, Va.) 1892-1928, 1893-04-20

"A FifldtiOu Oh tCutll vi du Hull from
perfection in tube thirty inches in
diameter and thirty feet or more in
length is q grave fault that must be
allowed for in all the claborte circula-
tions, and render it almost useless in
many important respects. The sheet
steel for the tube, therefore, must
have it's strength and resistance cal
culatcd as carefully as the girders,
beams, and braces Of a great bridge,
and its quality must be beyond ques-
ton. In the case Of the Washington
equatorial for the naval observatory,
the sheets are about onc-twelith OF
an inch thick at the end of the tube
and increase in thickness as they APP
proach the center, where they are
over onc-tcnth of an-inch. Steel is
now used in all great TELESCOPES, be-
cause t meets all requirements best
1t is as plain and free from ornamen-
taton as the surface of a sleam boiler
The instrument is for use, not for
ornament, and fancy brasswork or
polished steel surface would
simply increase the labor of caring
for it with no gain iii unity. Besides
the expansion and contraction of brass
is too great to permit it's use in any
quantity.
The mechanical problem Of the
tube appears in different guics in
every part of the instrument. The
resistance of the forty-ton wrought
iron pier Oh which the instrument is
mounted, must be calculated, means
must be devised for taking up as
much as possible Of the thrust which
comes upon the polar axis, in order
that the movement of the tube may
be easy. This is done By a necklace
of anti-fricton rolls at the upper end
of the polar axis, while below the
weight is born by hardened stcll ball
bearings similar to those in use in
the best byciclcs but larger. Then,
too, it is matter of no small leica
cv to so balance tube weighing
five tons, as does the Lick, Or six, as
will the i'erkes, that it can be moved
readily BY the touch OF the hand, and
the whole instrument be operated by
one man for hours at time. These
arc all the problems Of the mechanical
engineer, yet strangely enough they
had hardly been approached from
that standpoint until the Cleveland
builders began in constructing Il small
instrument for their own use eight
years ago.
\ telescope mounted equatorially
has the polar axis, directed exactly
to the pole Of the heavens, that cen
ter about which the North star cir
ccs in it's small orbit. The tube is
mounted parallel with the celestial
equator. These axes arc arranged
with gearing so that the tube can
swing around them to almost any
angle. AS it revolves about the po
polar axis it changes in celestial lon
gitudc, or right ascension, and its
movement on the declination axis
marks it's cclcstial latitude, or declin-
alton. The graduate circles fitted to
these axes enable the astronomer to
measure exactly the point in the
heavens to which his instrument is
directed. The large coarse scale is
shown on the outside and does for
rough calculation, but the utmost
accuracy, down to fractions of Il second
must be secured, and for this a much
finer scale of silver is fitted inside
the other and graduated so delicatcly
that it must be read with a micro
scope. By very ingenious contri-
vance this fine scalt is Illuminated as
necessary by a small incadccscent
electric light. These inner circles
require the most careful and delicate
workmanship, comparing in some re-
.spects with the mechanism of a watch
and are the other extrem from calcu-
lating the strength of steel and the
necessary weight and dimension of
the wrought iron pipe.
Within the great pier is the driving
clock, another remarkable piece of
mechanism. By its power the great
tube is swung in precisely the motion