The morning news. [volume] (Savannah, Ga.) 1887-1900, 1896-06-07

and patience of modern workmanship
have succeeded in overcoming obstacles
in telescope making which fifty years ago
were thought TO be insurmountable. In
al refraCung telescopes the one part
above all others that costs patience, skill,
and money is the object glass. All the
other parts are comparatively non-eXpen-
siVe and easily made. In the first place
1t is exceedingly difficult to obtain the
glass discs free from flaws and fatal diff
terences in density. In large glasses the
least defect SpOils the whole disk. There
is only one firm in the world, that of NJ.
Zen in Paris, which makes the discs Tor
the largest telescopes, and even this firm
in casting the disc for the object glass
OF the great Lick telescope in 1885 made
nineteen failures before one was produced
sufficiently free from defects for the pur-
pose But after the rough disc is sue
cessfully cast comes the skillful and deli
cate work Of grinding and polishing. For
large glasses this is a labor of months.
The final touches in polishing and shaping
are given, strange as ii may seem, by the
fingers, and so accurately must this be
done that in the final test every ray of
light which passes through the tense
must fall upon a spot not larger than
pins head perhaps fifty feet away. Here
in lies the differences of skill in different
manufacturers, and in the quality of the
instruments themselves AlVan Clark &
Sons of Cambridge, Mass, have long been
regarded as the most Skllltul manufac-
turers of telescopes in the world, and
their superiority consists in so shaping
and polishing the object glass as to cause
II to give a sharply defined image tree
from distortions and 1aulJS OF Color. 10
give some idea of the size of the largest
telescope in the world that recently given
by Mr. Charles T. Yerkes to the Chicago
University, It may be stated that the OBJ
1eCt glass is forty inches in diameter and
was constructed by the Clarks after Ia
Dor of several years and a cost of more
than $50 600. The telescope tube itself Is
of steel, sixty four feet long, and ffty-two
inches in diameter at the center, t8pering
towards the ends. The entire weight of
the telescope is six TONS exclusive of the
lenses, and the total weight Of all the
parts is seVenty-iYe tons. And yet so
deiicately poised is the pOnderous tube
that a child might turn 1t with ease. The
writer upon a visit TO the great Lick OBJ
servatory in California last summer tried
the experiment of moving the great tele-
scope with the little finger, and found no
difficulty whatever in causing the huge
instrument 10 respond TO an easy touch.
The power of a telescope depends upon
the ratio between the focal lengths of the
object glass and the eye-piece, while the
brightness of the image depends upon
the size of the objective. The brightness
of star seen with a tWo-inch telescope
is 100 times as great as when seen with
The naked eye With a four-inch glass it
is 400 times as bright and with a thirty
siN-inch objective, like that of the Lick
observatory, it is g, 400 times as bright
mat is to say, stars can be seen with
ne Lick telescope which are $4,000 times
Idlnter than the falntest stars visible to
the naked eve.
The highest power which can be used