New-York tribune., 1875-02-25
TWO GIANT TELESCOPES.
THE MANUFACTURES OF GREAT 1NsTRu-
MENTS.


CAN MANUFAcrURERs-THE CAKE AMI A--''
EXPENDED ON LARGE LENS.
tyRom AN OCCASIONAL CORRESPONDENT OF rHs rkiSoSN'
RosroN Feb. 5.-When Galile0's first tele-
o,o xas made which enlarged object less than hve
s,ame,ers II astonshed the world Ana when ne nnany
sueceeded in making one that magnined ABOUT ~ oia
eters IL was said that the highest maghhyns power
nad been reached and plausible reasons were gwen 10
-unstantste the statement. When, somewhat later
rranenhfer made the celebrated Dorpat telescope OF
Russia with an object glass of % inches in aperture Its
anormous power was the cause Of great excitement
among astronomers throughou: the world The famous
Chicago telescope with its 1sinch aperture, made by
Ozark 4 Sons, at cost OF slso0O has TIL lately been
a, the head OF great instruments OF this Glass; Az
Gatesnead near Newcastle. England, Mr.. K s. NewalPs
telescope made by Cooke Sons of York, with 25nch
aperture has for several stood as the largest IN
the world, though Of inferior quality and power AT
present the instrument in the Naval Observatory AT
Washington and active operation there gives 10
sbe United states the distinction OF having the largest
and effective refracng telescope that was ever
constructed This. too. made by MesSrs CarK VINO
have now nearly completed another OF similar eaoer
ordered by L. J. Mccormick Of Chicago, OF McCormlcKs
reaper fame. Ths IL Is understood, VIII DC gwen " 0No
of the Virginia universities
Tnese twin "monsters Of the deep"-sky not sea-
will IN every important particular be the counterparis
OF each other. The only noticeable onerences ate' 'e
Washington instrument has an aperture OF 70 inehes
while the Mccormick has OF little over 70 Dut only
enough to have said that is the largest in the wofd
she compound objective, ooeetglass, in the latter
weighs 40 pounds while that OF the former weighs SV
pounds In each, the glass with the tube in which
"A inserted weighs about ton, aud the whole weight
may be roughly estimated at four or five TONS Each
bas o focal length Of about thrtythree feet The cost
of the Government telescope $4,000 in currency
That OF the Mccormick will be $4,000 in gold The CON
tract was for both at the same time about four
years ago. and the price gold being estimated as
81 then stood Mr. Mccormick chose to pay the amount
In gold when his instrument should be completed The
obectyes alone when completed worth $4,000 each
and are capable OF o magnifyiDg power OF 1000
aeters though, owing 10 the interference OF tne at-
nosphere a power Of over 1900 will seldom be used
but even this will the surface OF the object
viewed, TO 2250OOO times its natural size.
The establishment that gives birth to these monster
telescopes is situated IN Cambrdgeport. Mass within
easy rife range of Boston State House 1t Is an unpre-
tending structure plain brick two stories high about
40 feet long by IS feet wide. with an OF the same
WIDTH and 30 feet long. and small one-sory ROOM per-
haps l5x0 All the power used in this factory Is hve
horse power engine, Of which more than three-horse
power Ia seldom needed. The firm is composed Of Mr.
AIvan Carkand his two sons. They employ at present
about halfdozen hands, and have in the busiest
times more than ten The senior Mr. Clark now over
~ years Of age and did not begin telescopemakng till
he was over 40 years old. He has acquired his
and skill without instruction. He has never
seen lens in process Of construction in the hands OF any
one out OF his shop Yet here made
whioh no other maker in the world has surpassed or
equaled.
The object glass is by far the most difficult part Of the
work Of telescope making. This is composed Of two
Lenses of and the other Of flint glass, the
former disperse scatter the coors in the ray OF
light and the latter to refract or bend the rays 70
focus. The combined effect s 10 magnify the object
and at the same time to destroy all the rainbow cOlors
thus presenting the object 10 the observer in white
hight or its natural These lenses made from
m immense mass Of molten glass; called pot" which
of course looks like lens than rough block OF
marble resembles q statue. The glass IN this massive
form made in Birmingham, England, by Chance
Brothers Co. This firm made the glass Of which the
English Crystal Palace constructed. For lenses
parts selected from the molten mass as nearly pure
possible and nodded into rectangular blocka Even
In this apparently simple process there is need or great
care and skill The "pot" Of melted flint glass, which
weighs from 6oO TO 2OO0 pounds, must be constantly
stirred tin chemical action, which would fill the mass
with bubbles ceased and till the glass has be-
come stiff In cooling that 1t be stirred no longer
To give some idea the difficulty Of this seemingly in
sgncant part OF work needs only be said that the
glass for the lens Of Of the nch telescopes cost In
Its rough massive state no less than $1,000 $500 had
70 be paid down before the operators would undertake
She task ALL and unsuccessful in 10 trials they were
20 be released from further obligation.
On arrival the factory in this country the block OF
glass is cut by the revolution Of circular disk having
apee on the edge OF its lower surface, which, with
sand for teeth cuts into tho glass in way similar to
that in which marble is sawed This gives the glass q
disk-lke form. ana its first remote resemblance to
lens This saving cutting is done by steam power
a plate an inch thick be cut in one-half or three
quarters of an hour. II is next ground down by the
revolving Of ooncave plate pressed upon It, one surface
at time till IL becomes rough doube-convex lens. 1t
is now Opaque, like ground glass, and is afterward
xround or smoothed down TO ne surface by means OF
emery and then polished IN hand process by rubbing
with coal tar beeswax and rouge. When lens is suf
hcently polished to admit Of the transmission of hight
10 corrected for cromatic and spherical aberra
ton, or confusion among the rays. The chromatic de-
feet the showing of the colors OF the rainbow such as
seon in looking through the triangular glass pendants
10 chandeliers. These would interfere with tho
view of the object. This defect is corrected
by careful adjustment Of the relative thickness of the
crown and flint plates Spherical alteration gives an
upnaturally rounded curved appearance TO the OBJ
tet This is the fact that the rays OF light pass
,ne through the outer part Of the lens brought to
than those passing nearer ts center The
distorted rejection of the face look upon the sur
face Of polished teapot into the bowl of clean tea
spoon is an Illustration Of spherical alteration While
The work Of bringing the glass 10 the general form Of
lens and OF polishing it, is comparatively simple,
the highest s and strained to their utmost in
properly correcting these alterations And is in this
very particular that Messrs. Clark Sons excel all
ether telescope makers.
As no mathematical rules aid IN the perfection Of
the lens this work can be effected only by wearisome
system Of tests continued daily and hourly for weeks
and months. Defects thus carefully ascertained
and removed. But the required notifications are so
slight and the work delicate, that hard the glass
ts the workmen dare attempt nothing violent than
amply down its surface by the application OF
wet rouge with the finger tips and often the rubbing
that removes defect IN one place produces another
near n The omoupt Of surface that worn away in