West Virginia argus. [volume] (Kingwood, W. Va.) 1877-1946, 1879-10-25
Great Telescope Glasses.

The glass for the new refracting tele
scope ordered by the Russian Government.
when completed, will be the largest in the
world. Its extreme diameter will be from
thirty one and onc-half TO thirty-two inches,
with clear aperture of thirty inches.
Three years and one-half are allowed for
its completion-two years TO procure the
rough disks and eighteen months for grind.
ing, polishing, correcting, &c, with an cX.
tension of time, provided good and sufficient
reasons are given for the failure TO finish
within the specified period. When finished
the glass will be mounted i'm Hamburg.
The cost of the glass alone will be S32, 900.
The material for the glass will probably he
furnished by French manufacturers. the
Clarks finding their disks To be most trnst-
worthy. AS the procuring of glass of a
density as nearly uniform as possible, and
free from flaws, is of the utmost importance,
Mr.. Alvan G.. Clark left for Europe to as
certain the prospect of careful completion
of that part of the contract He was nc
companied by Mr.. Strive, the Director of
the Russian Imperial Observatory at Pull
kowa, who made the award TO Clark &
Sons, and will return in about six weeks.
The method OF making glass OF this size is
very interesting The raw material is
carefully selected and melted in an ordinary
glass pot, allowed To cool and then broken
out IL is ono emOre melted and cast into
rough plates These are placed i'm n mould
and heated until they are waXlikc in con
sistency. Then they spread out and fill the
mould, making what are called the rough
disks. This is the shape in which they are
received by the Clarks, whose labor begins
at this point. The disks are first made
perfectly circular by means OF a revolving
disk of iron, with the aid OF wet sand.
They are then roughly ground on an iron
plate, fed with sand and wa'cr. to some
thing approaching the shape they will have
when completed. Then comes the fine
grinding with emery on another iron plate.
This part Of the process lasts from six
weeks to two months, and the rest of the
time is devoted TO polishing, testing and
correcting. The polishing is done with
rouge on an iron tool, covered with n fine
layer of tar and pitch, and hand labor must
be employed. When the glass has received
its first polish it is set up and tested, and
from this time on the work is n succession
of testing and correcting, repeated until the
desired result is reached In this operation
great caremust be taken, for an inaccuracy
amounting to but hairs adthinthe thick
ness OF the glass at some particular point
would be sufficient TO seriously iniurc ii and
require months to bring it to its former state
Of completion. If the glasses were of alb
soutely uniform density throughout, the
operation would he comparatively simple.
But such piece of glass il is impossible Ia
tnd, and as each variation in retroactive
power must be cqualiZed, the glass needs
TO bc corrected in nearly every point of its
surface. AS the glass is tested after each
correction, an immense amount of patient,
careful labor is required. Again, the con
ditions under which the glass is TO be used
mnst be taken into account, and also the
state of the atmosphere and the temperature
when the tests are made, conditions which
are never twice alike. AS telescopes are
most used before midnight, their detectives
are corrected for a falling temperature.
One OF the Clarks said that glass which
would be called in fair condition might re.
ceive several months labor before being
what they would consider perfect, and vet
IN that time the amount of material removed
would not equal One-tenth of grain in
weight. The largest glasses now in exist
ence are the objective at Washington and
one made by the Clarks for Mccormick.
Dnt still III their possession, each of which
is twentysiX inches in diameter. When
this and the Russian glass are completed, OF
The four largest glasses in the world, three
VIII have been made by Alvan Clark e Sons.
The contract made with the Russian Gov
eminent with the Clarks was concluded
September !. 1t is provided that the def
milton OF the glass shall not be inferior tc
that OF the telescope III the Naval OBSERVE.
tory, and the amount Of light shall be
greater In proportion to the increased ares
OF the objective, allowance being made fol-
the absorption of light 10y the glass. When
the rough disks are ready for figuring.
NJ. Strive is TO receive for his approval the
plan for fixing the objective glasses In Their
cells. Nj. Struve has the right 40 designate
the ratio of focal length of the objective &c
It's aperture, said ratio being not less than
- to /, nor greater than 20 to /, and the
Clarks must make the focal length conform
to this ratio within one-fortieth of its whole
amount If VI. Strive desgnates no ratio
the Clarks shall give such focal length that
the ratio shall be rs to !, within the limit
OF one-fortieth. NJ Strive NAV also DIES
lgnate what two rays or parts of the solal
spectrum, shall be brought 10 one focus by
the combined actions of the lenses. and if 4
fail TO do this, the makers shall fashion Tn,
curves OF the glass 50 as to give the mos
perfect achromatism. 1t is provided tha
the Clarks shall, about the time of the com
pletion OF the objective, construct a rough
reversible equatorial mounting for it. inciu
ding tube of such size, form and thickness
as the Russian Government may direct. In,
whole to be 80 arranged that the obiectiv,
may be safely and conveniently tested b,
observations Of the stars az least one hon
on each side of the meridian, The paw
ments for the objective were agreed 10 i,
paid as follows: 5000 10 advance. 81. OOD
when the rough disks are ready for fipurin,
and SIS, 900 when the glass is accepted
For the rough mounting $1,000 will b.
allowed
Trout story