The Democratic press. [volume] (Ravenna, O. [Ohio]) 1868-1901, 1883-12-27
How Telescopes Are Made,

Prof. J. K. 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
dred people. The subject Of the lee
ture was The Great Telescopes of the
World" and it was Illustrated with
dissoIving 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 u description of the manufac-
ture of the different parts of the mod
ern telescope, describing minutely 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 iron is coated with
pitch, and the glass having been first
roughly ground, is placed inside, and
the workman walks around the polish
er 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 Il
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 sim
grIlar, thinking OF the fame that this
man now enjoys, that it was in another
country that he first gained 4 repJta-
ton for fine work. Alvin Clark was u
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 Presi-
dent of Columbia College, and then the
head of the University of Mississippi,
gave Alvin Clark an order for a lens 10
inches in diameter. The rebellion pre-
vented the sending of the glass to Mis-
sissippi, and finally it was bought for
the Dearborn Observatory, ut 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 Il
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 appliances
of the Chaldean shepherds for determ-
ining The equinoXes, the telescopes of
GaIileo and Herschel, and Tyco Brahe s
observatory on the island of Huen.
Among the famous modern instruments
were shown the mammoth refractors
in the naval observatory and at Prince
ton college, and the refiectors at Paris
and MeIbourn. In conclusion, the
speaker, after mentioning the divided
opinions as to the merits of refractors
and reflectors, said: ''Ihe future opti-
elan who may discover the means of
avoiding the secondary observation and
change of color, the present drawback
in refractors, will demonstrate the par
amount utility of the refractor, OF
the one who finds a way to provide
against all atmospheric changes in the
reflector may give the palm to that
glass, but up to the present time all
practical tests have shown the superior
| ity of the refractor for astronomical
work. Prof. Rees was loudly APP
| plauded. d.-NetO York Times.