National Republican., 1873-12-15
TIE TELESCOPE.
ITS HISTORY AND CONSTRUCTION.

The sixth lecture Of tho course by Professor
Ncwcomb before tho Columbian University was
delivered On Friday evening. Tho Professor SAID
that the present lecture woud he devoted TO the
history and construction Of the telescope.
TIVE REYRAcTiSo rrtEscurR.
The invention OF the telescope is Involved IN
some obscurty, hut the common opinion Is that
one Jansen, spectacle maker in Holland, Euad
q combination OF glasses which wruld bring dis.
tant objects nearer to the eye. lie made known
his invention tQ Prince Maurice, who formed the
idea that II would be Of great use In war, and
therefore engaged the inventor to keep II secret
Tn s.S no., o. sSen nrnr ~ syenIs ~
self to relnyentIny the Instrument, and found
that combination Of . convex lcns Of long focus
the desired effect. This was about the year 1910.
lie pointed the insirIment at the heavens and
vas reverted 6y tho discovery Of the phases q
stars Invisible to the naked eye.
The subsequent Improvements in the telescope
were then described. IL was explained how the
image Of a distant object could 10 found ia The
locus OF lens, rays Of light enalatlng ron the
i,nsse. precisely a. they would from the o,isinal
real existence, could be viewed by a maRniiyinH
-,nss. lust ~ weyiew small object by u common
ksndfcns ,r1 ssstRss 'sIsssRs ,sls.Sonsy sas sy msL
since, eonslst essentis,.y y ~ s....-. large ob
jcct glass to form Image q the distant object
and an eye pisss Q, wo ,%a m , idnsss win h whisn en-
changed at pleasure by siIuply using IN cye-lens
Of the proper focal distance.
The earlier astronomers found II impossible 10
produce a weli-dehned image In the focus OF the
Telescope account OF the lens deeompOslng the
llsit Into It's pr.smatic colors, and thus forming
Number Of images of various eolors which were
confused together. Hut, amer many trials, IL was
found by an Engllshman named PollHnd that
eolors about twice as powerfully as crown sisss.
In consequence Of this property lfa double convex
sn. o. crown glass y )ained 20 eoneaye lens Of
eGecss q the tive isases in dccomposing tho light
viii nsutralise each cthe[ and al the colors w.lI
sss s.s~. nn s %STf @ ss
rays to focus. Thus we have the sehromatis
retrAo.,ng teleseoPs ~ II s nov made. The inven-
| tion ot
rms RgrLrCrIso rKLRscorE
sapsrSTs % III named arssors % III ri. ins,rS. TS
| ment eouiists Of eoncave mirror, which reflects
| the rays 10 a fceus between the mirror and the
IN The focu; This Image can then be rsc.iv cd BY
an eye-giass precisely :. the image In he keus
ave an Observer must pisee his head betweea the
i object and the mlrror, and hence cut on large
Inr,ion Of light from the mirror. To avoid this
por nsar Inc T ioess which Gsasetsd the rays !"
lateral direction, 20 that the observer could SEQ
?, S nsoa sas .s e ts's
sss Ss q Is: ,sss % ss sss srs sss
1
sand al the top OF the telescope, And heHcc, In
the larser telescopes, mast be forty os ANY feet
In the arssssian telescope the diueui,y /.
near the focus ef the large one, 20 a. tothiox the
hole Is cut through i In which = ssessi iasss
| Is formed, which tho observer Views with an On
sn 4. @ aa ,s' % .s.i
than half Of II can reach ths eye Of the obsssvcr
| HEpRAcroRs vs.. RsvLEcroRs.
the rejecting aud reiractisg telesespss. Asr 2
bIaisi, as those " HsrsehsL Rosss, and LAs,sl
lslong to the class Of rsdeetors. 10 praetlss
. 'ns:s sss a. rasa,ss nsssa 70 ~ ~
the lecturer esptes,ed himself as sontinuail,
sss soSS,.s @ E @ SS eS%p.fsS Ss vi
that of Lord Rsaae He would reply to this
s.s 'ssF x, 70 .sS s dasr's
possible to institute eelspstisoG between thcm
and, second. that Lord Rose. telessope had no
rensetors Of Two iest and of four feet diameter
Sd sS. .s 'ss sl = K. Ssa sS %a's
new Washington telesooye is equivalent TO
Theoretically perfect reflector oi three tee
siiss =. any ns u eSoss srsss % rsss D
The Professor then bfieny described some Of III,
principal rsirset,ng ,sleseop., A pair & o. hissl @
The obstfyaiories Of Oaubriags and Pui RVwa b!
MsrI aud hshln, Of Munich, were considered
woadsr At the time; for tven,y years IA.
made the largest which have been brought int
sueeessful operation. But il lsoo MI. AlyA
CLARK, VI Cambridge, Mass, made one Of eighlse
inshes, which WAS sold TO an observatory u IN
eagO, Thi. sirs was soon ckosodcd by an tngilr
trm, who pIade one Of no less than twspty.iis
lI"hes uL,rlurt, for private gentleman In EIa
land. Determined 10 exceed every one, M
CLARK has how made one VI iwehty-six inches, q
the observatory here. which Is therefore IN
lnrgss rejecting telescope ever SUCCESSFULLY con
p!eted