New-York tribune., 1874-04-27
THE GREAT TELESCOPE AT WASHINGTON.
BY PROF. SIMON NEwCoMB.


BY PROF. SIMON NEWCoMB.
The initiatory movement in the construction
OF the great telescope early In July, 1870 when
Congress authorized iorIt appropriation OF $4,000
The contract was made with Ayan Clark & Sons OF
Cambridge Mass, manufacture II. The price agreed
upon the telescope was $4,000. Chance Co.
OF England agreed furnish the glass they being the
only makers OF achromatc glass suitable for large
tractors There many failures in casting the glass
disks and fully year elapsed before Chance Co. de-
lyered glass to the Messrs Clark but even this
moro expeditions than has been the case In other In
stances at least order given about the same time
had not at last accounts been filled. Avan Clark
Sons finished the great telescope October 1872 It is
hopes that mad been entertained concerning It,
The telescope is mounted on what is known as the
German or rather the Munich plan; but this has not
been rigidy adhered 10 where improvement was pos
sibe. Certain important notifications have beea made
some OF these were devised by the Messrs. Clark, aud
one was adopted from Mr. Cookies great telescope at
aeshead. As result OF these improvements, the OBJ
server can point telescope by means OF the circles
alone nearly that object shall be In the field OF
quired TO leave the floor or TO look at the object.
The question is frequently asked, How does the new
hcu answer since there are no refractng telescopes
In this country OF comparable dimensions Ihe question
10 the comparative efficiency OF refractlng and re-
ectng telescopes is frequently raised IL must be adj
that great rejecting telescopes give variable
results very apt to prove sstl-facory. As
instance OF this II we examine the record OF herscnes
work, We ma that nearly inc Nnole OF IL WIS
done his two-fo0t reflector; shall almost arrive
at conclusion that all tae work accomplished with
the four-foot reflector might have been done with the
smaller instrument. The same comparison OF results
leads to "a similar conclusion with regard 10 the four
foot reflector OF Lassepro0abiy the largest
structed. He had under the clear skies OF Malta made
many important observations; but when he took his
fourfoot reflector there, hoping with 1t 10 verify his
discoveries. 10 does not distinctly appear that he sue
ceeded. strive after looking through the f0urfO0t tee
scope, wrote that IL not in any remarkable
degree powerful than his Blnch nstru-
menJ at Potaya. The only exception TO this gem
eralization IL the fact that the fourfoOt in
sr1ment Of Lassell did really discover the two inner
satellites OF Uranus. Prof. Newcomb having redis-
covered these with the instrument, and thus VERT
fed LassePs discovery, thinks that they could never
be with l5uch refractor. In the new telescope
the outer satellites Of Uranus look II OF about the
that Urs@ minors appears TO the naked eye. Tho
smaller satellites, strange TO say, have been best
when the moon shining, aud its light plainly
apparent In the telescope the nrt Of these appears
about half as bright aud the second about onethrd
bright, Titana.
friends have asked whether there Is difficulty In
the Washington telescope account OF spherical aber
ration. This proves to be very small factor total
amount II less than that produced in the lens
atmospheric variations OF tomperhtufe-dn effect which
1. noticed when work first begun with tue
OF an evening" but which rapidly wears away the
glass acquires the uniform temperature OF the rest OF
the Instrument IL seems TO be only the the
edge OF the glass which are thus affected. Prof
como has ooked through many other refraetiDg tele
scopes by way of eomparison aud after full eonsidera