The Norfolk Virginian. [volume] (Norfolk, Va.) 186?-189?, 1897-06-29
OUR BIG TELESCOPE.
Foreign Appreciation of Americas
Most Powerful Lens.
{London Standard.)

The completion Of the great object
glass for the Yerkes Observatory is n tri-
umph for the opticians, and provides
American astronomers with the most
powerful instrument In existence. This
huge lens, which has already been
mounted and turned OH the planet Jupi-
ter. has surface diameter Of forty
one and q half inches, and weighs 515
pounds. TO shape and polish it has oc-
cupied five years. The Lick Obscrva-
tory must now take second place. al
though its telescope, with lens yard
in diameter, is ahead Of all other refrac-
tors In the world. That instrument,
named after a wealthy American who
left the money to construct it, was first
used about eight years ago, and, even
though 1t has been deposed from the
first place, still possesses one unique adj
vantage for purposes Of observation
1t ls placed In an almost ideal situa-
ton. One of the prime requisites of an
observing station is the absence Of cloud
or fog--the variable character Of our
climate being constant impeachment to
British astronomers. The fate which
awaited the savants|who went to Nor
way and Japan TO observe the late
eclipse Of the sun has often been eX-
perienced at Greenwich and every other
observatory In the United Kingdom
But the Lick observatory has been built
at an elevation OF rather more than 200
feet above the level Of the sea, and in
the clear air Of California. The Yerkes
telescope is not SO favorably situated
as its elder but smaller brother, since
1t is set up In the lake regions Of the
United States. 1t is by far the largest
In the world among the refracting tele-
scopes Less than twenty years ago the
Washington observatory. with it's OBJ
1ect glass twenty-siX inches across, had
been supposed to defy competition, but
Vienna Immediately trumped with an
extra inch Greenwich has one twenty
eight inches. Nice and Puftowa have
glasses of thirty inches. but in the opti-
clans race it will now be America first
ana second. the rest nowhere. The me-
chanical difficulties in constructing the
Herkes lens must have been most for
lndable.
To begin with. the making Of such a
mass Of glass with the requisite per-
fectlon Of material is no trihe. while
the grinding and polishing required ma
chinery OF marvellous accuracy For q
long time these practical difficulties kept
refracting telescopes comparatively
small In size. Years before Mr.. Newalrs
instrument with its object glass twenty
five inches III diameter, was set UP at
Gateshead. rejecting Telescopes with
mirrors Of much larger diameter than
even the Yerkes object glass had been
constructed. In front of Birr Castle
stands the giant among reflectors, with
tube down which a man. II only Of the
average stature. can walk upright BY
its side Is another. which In any other
place would also be esteemed n giant
with q mirror about a yard across The
mechanical difficulties with this class OF
telescope are hardly less than with the
other one; for the surface OF the mirror
must be shaped with the greatest eX-
actness. and the parabolic form is diff
ficult TO obtain-though the machinery
used In Lord Roses workshops which
was exhibited In operation TO q party
OF visitors a the tercen tenary of Trinity
College, Dublin, looks surprisingly sim
pie. Another, and often serious, difficult
ty with these telescopes it the tendency
to dimming. or loss Of polish, on the
surface OF the mirror. From the latter
drawba elk object glasses, OF course, are
free. though they require more delicacy
and accuracy Of construction. and have
their ouw special trouble in what Is call
ed chromattc alteration. This, If light
were not compound. would not exist, but
rs ordinary light is mixture Of rays,
differing both in color and refrangibiIity
the lens acts as prism and produces
tints. The difficulty has to be over
come by the use of different kinds Of
glass, so that the faults Of the one are
counterbalanced by the faults Of the
other We must now wait and see what
THIS new instrument can accomplish.
VIII 1t solve the secret Of the canals in
Mars? VIII 1t add TO the already too
numerous asteroids, discover more satel-
lites, settle the question Of an inter
Mercurial pranet, and reveal the true
nature Of saturn's rings and Jupiter's
belts?