Walker Lake bulletin. (Hawthorne, Nev.) 1883-1926, 1897-11-24

CHARLES I. YERKEs.
noticed in looking through the glass of n
window that here and there will appear
distortions of objects without the cause
being inequalities in the glass or differ
enees i'll its substance. In an ordinary
window glass, II distortion of this kind il
matter of no consequence, bur in the
OBJECT glass of telescope, il the material
at one point is II tritle denser than ut an.
other, or II in cooling, the glass becomes
harder or softer at different places, the
result will be fatal to Il correct obserys-
tion. 1t is said that nearly forty disks
were tested before a selection was finally
made Of one to be used for the Yerkec
telescope. The testing of the disks is IL
matter of mathematical accuracy, the glass
to be used being placed in a room dark
ened, save for II sinali light at the other
end, then careful instruments are employ
ed to test every quarter inch Of the en-
tire surface. Sometimes there IS a SUPER
hcial haw. which disappears Ii the grind
ing, but IL the defect is in the interior of
the disk, that piece of glass is worthless
for astronomical purposes, and is set aside
at once.
After the selection of n perfect disk
the grinding begins. In its early stages
machinery may be employed TO reduce the
disk to an approximately correct form. but
after the coarse grinding is finished all
the rest of the labor must be done by
hand, a work of great length and inex
pressibly tedious. The object glass of the
Yerkes telescope required nearly two
years and a half of constant daily labor
for its completion, and the cost was S7O.-
900. After the mechanical grinding IS
completed, the workmen begin with emery
powder and leather pads, and by slow
circular motion gradually work down the
surface of the glass to the required d-
mensions. The tediousness of grinding
down a disk of tough glass by slowly NOV
ing ones hands over its surface is more
exasperating than the hardest labor. Day
after day, week after week. month after
month, the mechanic, skilled mechanic
at that, spends his time in rubbing the
surface of the glass. He cannot see that
he has made any progress from month TO
month; for within a few weeks after he
has begun the glass appears as brightly
polished as possible, but the skilled eye Of
the superintendent can detect the differ
ence between the highest polish attaina-
BILE and any degree below that 1t is not
only, however for the sake of the polish
that the workman labors, for the glass
must be worn away to the required di-
mensions and the most delicate mathemat-
ical instruments are daily called into play
to deermine the progress that has been
made. In six to nine months the progress
becomes perceptible, in eighteen months
the work is far advanced, at the end of
twenty-four months of. steady rubbing.
the glass is approaching completion. Here
and there, however, in spite of the care
with which the rubbing has been done.
there are inequalities detected by the in
struments, if not by the eye and these
must be remedied by little extra rubbing
here little less there. Finally, as a con
Guiding operation, the workman spends
weeks rubbing the surface of the glass
with his bare hand; TO reducing sub
stance, no emery, not even the finest and
softest powder, will answer the purpose;
the bare hand alone must complete the
operation. When the hand of one work
man is bereft of the skin, another takes
his place, and the bare-hand rubbing goes
on for weeks and months. Finally the
instruments detect no further inequali-
ties the tired hands of the workmen rest
and regrow the cuticle that has been lost
the glass is finished.
At the workshop it is mounted in a tenn
porary tube. then taken down, and, il
necessary; retouched at different points
and packed for shipment Seventy-thou-
sand-dolar object glasses for telescopes
do not travel in freight cars; the jolting
would ruin them forever They are pack
ed with dense layers of cotton batting, in
boxes especially made for the purpose
are transported in soft-springed vehicles,
al Il walk. to the nearest railroad station,
and then ride in a palace car to their des-
tination. The box is set on edge, and ut
every few miles is turned SO as to pre-
| sent another edge of the glass TO the jar
ring motion of the train, lest, on account Of
the great weight, the substance of the
| glass should be changed in texture by the
| internal strain. a force of skilled me-
| chancs accompany the glass to its desti-
nation; no one is allowed TO touch it but
| these men, who themselves attend to the
work of adjusting it in the telescope and
| then of mounting the instrument. Ere
| il starts Gil its journey it is insured for
| its full value against accidents.