The daily Cairo bulletin. (Cairo, Ill.) 1878-1???, 1883-12-11
How Telescopes Are Made,

Prof. j. X. Rees, of Columbia Col
lege, lectured last night in the hall of
the Packer collegiate institute, Brook
lyn, to an audience of about six hun
bred people. The subject of the lee
ture was 1.-The Great Telescopes of the
World" and it was illustrated with
dissolving views. The Professor read
from manuscript in an easy and clear
voice, and dressed his thoughts in sim
pie and appropriate language, using
but very few technical terms. He be-
gan with description of the manufac-
ture of the different parts of the mod
ern telescope, describing infinitely the
process of grinding the lenses. In
America this is done by means Of an
iron polisher, made to fit the convex of
the lens as nearly as possible. The in
side of this polishing ironi is coated with
pitch, and the glass having been first
roughly ground, is placed inside, and
the workman walks around the polish
err pressing on the lens. In Europe the
polishing is done by machinery, the
lens being held against the revolving
polisher This, it is claimed, insures
more uniform surface, but experience
has demonstrated that no lenses yet
made have given such general satisfac-
ton as those ground by Alvin Clark, Of
Cambridge, Mass, and all glasses from
him are ground by hand. 1t seems SIN
gular, thinking of the fame that this
man now enjoys, that it was in another
country that he first gained reputa-
ton for fine work. Alvin Clark was a
portrait painter, and took up the study
of optics as diversion. For ten years
he turned out glasses without attract
ing any notice, but at last the merit of
his lenses was published by English as
tronomers. just before the outbreak
of the war, Prof. Barnard, now Pres-
dent of Columbia College, and then the
head of the University of Mississippi,
gave Alvin Clark an order for lens II
inches in diameter. The rebellion pre-.
vented the sending of the glass to Mis-.
sissippi, and finally it was bought fol-
the Dearborn Observatory, at Chicago
where it now is 1t is singular fact
that New York city, occupying the
commercial supremacy that it does
cannot boast of anything in the line Of
astronomical research; but it is hoped
that in the near future somebody will
endow an observatory which will be 8
monument more enduring to the do
nor's memory than the commonplace
successes of life. The views with which
the lecture was illustrated embraced
photographs of the primitive appliance!
IL the Chaldean shepherds for determ
lining the equinoxes, the telescopes Of
Calico and Herschel, and Tyco Brahe's
observatory on the island of Huen
Among the famous modern instrument:
were shown the mammoth refractort
in the naval observatory and at Prince
ton college, and the rehectors at Paris
and Melbourn. In conclusion, the
speaker, after mentioning the divided
opinions as to the merits of refractor.
and refectors, said: 1.-The future Opt
clan who may discover the means o.
avoiding the secondary observation ant
change of color, the present draw back
in refractors, will demonstrate the par
amount utility of the refractor, OF
the one who finds way to provide
against all atmospheric changes in the
reflector may give the palm to tina
glass, but up to the present time al
practical tests have shown the superior
ity of the refractor for Astronomical
work" Prof. Rees was loudly ap
plauded. -NeW York Times.