Port Tobacco times, and Charles County advertiser., 1889-02-22
FORTY.lNCH LENS.
1t Ia to BE Mounted at San Diego and
It's Object GLASS VIII BE the
Largest in the World.

Alvan Clark of Cambridge. the cele-
brated maker of telescope lenses, is
just now overwhelmed with PROPOSE
tlonS, each one of which is of greater
magnitude than any ever before
dreamed of. Since the mammoth Lick
lens was set up the people of San
Diego, Cal, have been anxious to out
do it. Wealthy citizens there have
offered President Brauvard of the Uni
versity of Southern California the funds
necessary to purchase 40-inch glass.
OF the San Diego instrument Mr.
Clark said that he expected the most
wonderful results To follow the mount
ing of this glass. II don't know why
it is" he said, but the atmospheric
conditions on the Pacific slope are
much more perfect than any of which
we know. Why. when | was ON Mount
Hamilton in the dead of winter | was
able Ia get clearer views of difficult
objects than | ever got here. In south
ern California, of all places in the
world. the biggest glass ever made
can be used with the utmost efficiency.
Southern California has two important
advantages over Mount Hamilton. In
the first place they have Il mountain
l,5oo feet higher. aud then the climate
is not so rigorous and observers need
not freeze while at their work. l. am
delighted Ia get this contract. not for
the pecuniary interest involved. but for
the sake of science.
Can You make glass larger in
diameter than the 36-incn one at the
Lick observatory"
Il.
many years now.' said Mr.. Clark.
land ! venture to assert that if | can
&c, glass of the proper size there will
be no difficulty in making tive-foot
lens-if my life were spared long
enough To grind it
Speaking about the glass he said:
"there are but four places in the world
where telescope glass is made. One is
at Birmingham. England. two are
near Paris. aud there is one iu Ger
MANY. | always buy mine Of the
French manufacturers. Ii Is necessary,
in the iirst place. to get a block of
glass absolutely perfect in every way.
The slightest flaw or variation in
density would spoil il for big lens.
Then II must be ground and polished
by hand-litcraily by hand in the
final stages. When the glass is cast
they break away the pot aud examine
the mass to see il il Is suitable to split
up into lenses. II must be Just right
or it must be melted over. The least
Indication of sediment will show that
IL is useless for large lenses. Ii hone
Is visible then they test IL with the
~ rrf-canr 10 seq IL itsis Of even
density throughout. II nil the con-
dI,ions are perfect then they split up
the block and get out large lens in
the rough. II they succeed in doing
this there is still greater danger that il
will be broken in the fir>t handling
to get it down To the proper size for
grinding and polishing After that
the worst danger of breakage is past
''lu order Ia secure tine best results
the ip-inch lens should not be much
thicker than the Lick leus. II de-
pcnds upon the length of the focus. so
| generally make my lenses thin aud
NV tubes long"
Mr.. Clark SAYS that, contrary To the
predictions of astronomers, the re-
fraction of the light does not interfere
with observations ut the Lick obserya-
tory. Not only have the observat
been good. but they have exceeded
anything ever dreamed Of
IF there are intelligent beings in
the moon." said Mr.. Clark. 1--WE should
be able to see their buildings. bridges.
aud canals. Ii is suggested by scien.
tiiic men nowadays that there may be
air and water and inhabitants on the
side of the moon which we never see.
Perhaps these people may explore the
desert which is continually turned
toward us. IL they do. and if they
build there or make big excavations,
We should be able to see their works
with t.is forty-inch glass"