The Ottawa free trader., 1883-12-15
How Telescopes Ar, Made.

Prof. j. X Recs, of Columbia Col
lege. lectured las, n,2 2it in the hall of
the Packer collegiate institute, Brook
lyn, to IN audience of about six hull
drcd people. The subject of tie lec-
ture was 1.-The Great Te csco0os Of the
World" and it was Illustrated with
dissolving views. The Professor read
from manuscript in an easy ard 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 minu.ely the
process of grinding the lenses. In
America this Is done bt means of an
iron polisEcr, made to lit the convex OF
the lens as nearly IS possible. The in
side of this polishing iron is coated with
pitch, and In GLASS having been first
roughly groun |, 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. Tris, it is claimed, insurcs n
more uniform surface, but experience
has demonstrated that no lenses yet
made have given such general satisac-
ton rs 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 enjo, $, that it was in another
country that he first gained reputa-
ton for tine work Alvin Clark was y
portrait painter, and took up the study
of optics rs Il diversion For ten years
he turned out classes 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 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, nj Chicago,
where it now is. 1t is u singular fact
that New York city, occupying the
commercial supremacy thai 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 lfa The views with which
the lecture was illustrated embraced
photographs of the primitive appliances
of the Chaldean shepherds for determ-
ining the equinoyes, the telescopes OF
Calico and Herschcl, 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 rehectors at Paris
and Melbourn. In conclusion, the
speaker, after mentioning the divided
opinions as to the merits OF rcfractors
and reiicctors, said: "The future opti-
clan 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, or
the one who finds Il way 70 provide
against ali atmospheric changes in the
reflector may give the palm TO that
glass, but up 10 the present time all
practical tests have shown the superior
ity Of the reiractor for astronomical
work" Prof Rees WAS loudly mp
plaudcd. Nc,C York VrnlcS,