The Wheeling daily intelligencer. [volume] (Wheeling, W. Va.) 1865-1903, 1897-12-06
TRLrsoopIo EYrslaHr.
How Far Can the AFnrieiai Eye % science
Pirrrathe Mysteries.


Self Culture: The telescope at the Paris
exposition viii bring the image of the
moon, as it were, Within mile OF the
earth,
It was formerly thought that the diam
eter OF the object glass of great tele-
scope could not be increased beyond ii
certain number Of inches without fatally
diminishing It's effectiveness, Object
glasses rest ON their edge. OF course, and
the weight of very Wide glass was. 50
great that Il decreased the density Of tn
lower pant o. IT. rim. on which It's weight
rested, and 60 modified the reftactlon of
thai part OF the glass, Refrachon Is the
bend or change In Its directlJh which a
ray OF light undergoes upon passing
through any deHssr body than the air.
formerly object glasses were made
very thick In the centre Of thsir eonyeNi-
ty, and 60 their local distance, or the
paint at which all The rays passing
through them crossed, was very near 10
the glass itself. The thicker an 0biec-
tive, the shorter the distance TO where
the focal point lies (bach of il in the
tube). With these thicker detectives
and their short focus, very low power
magnlrying eye pieces TO telescopes were
used-not over l,O10-diameler eye piece
to the lurges; instruments,
But lately Avian Clark and the Jena
manufacturers have employed very
much thinner detectives. Such objec-
lives produce a focal point much further
back from them In the tube 1T the tele-
scope And this change OF focal point
has given rise to the use Of eye pieces
OF 1000 or 5000 magnify!ng power. The
nearer the object to he magnihed Is
brought to an eve piece the higher
must be Its magnifying power
And so the old limitation Of slze--dl-
ameter-.in an objective have been over
come The objective OF the Flower
Observatory in the University OF Penn
sylvania Is eighteen inches In diameter;
that at Princeton, twenty inches: thar
at Harvard, twenty-four inches; that nj
the University OF Virginia, twenty-siX
inches: that at the Lick Observatory,
thirty-efght inches, while the Yefkes
objective IS forty Inches In diameter.
The glass which the Alvin Clark Com
pany GAVIN and his son are now both
utdil 10 INV llahlAlb w lhl
the Paris Exposition OF 1900 Is ilfty-one
inches In diameter. II is thin convex,
with long focal distance.
Detectives Of telescopes are duplex,
consisting of conveXlty OF crown glass
fitted tightly into one-sided concav-
ity Of flint glass, This arranGement Is
necessitated by the fact that rays OF
different colors have a different angle
Of reflection In passing through convex
crown glass. But these color rays are
intercepted by the flint glass backing,
and so the focal point Is preserved,
The glass Of these detectives must be
OF equal clearness or opacity through
out. Alvan Clarke told Professor
George r. Barker, OF the University of
Pennsylvania. (physicaD. that the deli
caey of his detectives was altogether
owing to his care In going over them
personally: and wherever he discovered
n comparatively opaque spot, Ie would
dip his finger tip In rouge powder and
gently rub the spot back and forth for
mlnute-so exceedingly susceptible 10
this very slight friction are such high
Ia finished and polished pieces OF mold
ed glass.
The cost of great detectives is enor-
nous. The Lick objective, which
stands fourth in the list, cost $4,000.