El Paso daily herald. (El Paso, Tex.) 1881-1901, 1897-10-21
HOW A LENS IS MADE.
Description Of the Careful Works Of
the TeIeScODe Building.

the Telescope Building.
1t would be hard to give an adequate
idea Of the skill and patience require d
in the manufacture of these great OBJ
jectiveS. Time and gain, wi n mimi c
care and pat eGce, the glassmaker
must try, for if there be a speck. p
bubble, d wave, or flaw If any KIND
no matter how minute, Mr.. Clark
would not accept j.. The procns of
makir lens is exceedingly 81 nple.
There is Little machinery and no sec ct.
First, tee lensmaker tests the disk for
striae-that is. he sets 1T up on edge
mid way Of long, dark room. At one
end of the room he places light, then
takes his position al the other end of
the room. An assistant now holds Il
lens between the light, and the disk,
and as the rays are itensified upon the
disk they magnify whatever streaks or
waves or inequalities there may be in
the disk. ana his keen and practiced
eve can determine whether the flaw is
in the body of the glass or near enough
to the surface to be removed by the
pOlishin process. Next he tests it for
polarized ght by simply taking it to
the other light, laying 1t flat upon q
polishc redwoo b d and viewing it at
proper angle through revolving
Nicol prism. If, is the prism turns,
The disk changes shades regularly and
evenly throughout its face, lit is good
optical glass but it shows cloudy in
spots or stresks it must be rejected.
Having stood these tests, the Glsk is
ready To be shaped. But first very
important problem in mathematics
must be solved. An order for a telescope
contains two essential specitications-
namely, the diameter of the object
glass and the length of ,he focus. If,
L. l,a fon
inch aperture and a tifty-fOot focus the
lensma ker must determine what curve
to give the glass in order that every
ray of light which strikes its
surface may be refracted to q common
point precisely fifty feet away. When
this is computed an iron casting is
made of the size and shape each side of
the lens is to be-a cOucave casting for
the converse side of tie glass, and vice
versa. This casting is turned on a
lathe and the disk is laid upon it and
revolved, steel crushings being strewn
between the two to grind the disk.
This brings the glass roughly into The
shape OF the lens. Then, with eight
cou of emery, each course finer
than the preceding oae, the disk is
GROUND with an adjustable tool or form
so constructed that the pressure may be
increased or diminished at any point.
=
mately its tinal form. This is all COM
coarse work. In max ng
he measurements at this stage Mr.. |
Clark employed an instrument that re-
gisters one thirty Thousand OF an
inch. No instrument can be M lde by
human hands foo me tsuring the in |
tini; sinai distances which are so i'm
port.nt in the final shaping of one OF
these great lenses. The human eye, |
nd ra1y- been and 1nntr ctinpd |
one at that, is the only instrument fit
to make these measurements.
Tne final shaping and poll shing are
done with beeswaX and rouge. 1t takes |
from eight en- months to two years 10 |
DO it. And then the final testing |
The lens is taken back into the long, |
dark room whence it was brought two
years before. Again it is set on edge
mid way of the rayless tunnel. An |
art ficial star-a point of lights plac-
ed at the lower end of the room. and at
he upper end, precisely fifty feet from
the lens, exactly where the focus must
be, an eyepiece is fixed. Now, the |
myriad rays of light from the star
must fall upoa every point of surface
Of the forty =inch lens, and each must |
fall at such an angle that they will be |
refracted to com mon point just ex-
actly fifty feet away, Ii single ray
tails the Dreadlh OF sp,der strand
away from that point the lens is de-
fective aud the lensmaker must find |
where that particular ray strikes the
surface of the lens, and then, with his |
lump of soft beeswax or perhaps with |
mis- thumb, he must lightly rub that
spot until this ray is turned into its
proper course, and this must be done
so deity, so exquisitely, that meantime
40 other ray is disturbed. 1t makes |
one's head swim to think of the fnene SIS
IF this work.