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# Title: Lexicon Technicum: Or, An Universal English Dictionary Of Arts And Sciences (shelfmarks Leibn. Marg. 71; ZEN Leibn. Marg. 71)
# Folio - , page id 806933011:0576
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OPTTCKS, is a Mathematical Science that ( plain.) When the Clals is in chis Pocture, it
TreatS oF the Sixht in gerreral, and OF CVerY
chins chac is leen wich direct Pays; aud explains
the leveral Properries and Fftects oF Vision ir
general, and proverty ot thar which is direct
ard ordinary: For When the Rays ot Lighe are
considered as reflected, the Science which ceach.
es their Las and Properries, is called Carop.
erictes; and when che Retraction oF Rays is con
Bdered, and che Laws and Nacure oF ic explain-
ed and demonstrated, the Science is called Diop.
erickes. S0 char Opriekes comprehendsthe Wr hole
oE vitich, Caropericts and Viopericts, are che
EWVO PATIS
OPTTCIS Classes. MIP. Nemton, in his Phi
los. Natur. Princip. Math. Lib. T. Schol. ad Prop. 98
Cays, Thac For all Oprick Dles, Spherick Figures
are the most commodious. IF the Object. CilaI-
ses oF Telescopes ere compoled ot tro Spherick
Classes containins Wacer becweenthem, perhapo
the Trregularier os che Refractions chat are made
on the Surtaces oF the Glates corards cheir
Fdges, may be accurarely enough corrected b
he Retractions ot the Vacer. And Puch Object.
Glasses are preferable to Elliprick or Pyperbolict
Glases, noc ontr because ther are casier and
more accurarely ro be formed, bur also because
cher resract more accuratelr those Pencils ot
che brishe Spor be projected just in che midele
oF ehe Fainter Lishe, the Cla(S is vell centered
BHE 1O Wtarever Side oF che faint Lighe ehis
brizhe Spor is projected, on that side is the ClaES
chickest, and on chac side lies chetrue Contre.
A Third Way
Os Examinins the Centres os Glasses, is vet more
Compleat than the former: For it does not ont
discover the Fault, (if there be any, as in lons
Object Glases tis very rare but there is, espe
cially is they be mroueht in the Form by the un-
suided TTand, and not by an Engine) but mith.
al it rectisies the Fault; and is thus:
Corer the Surtace oF the Clals with a thin
piece of Paper, in which chere is cur a ronnd
Holc oF about an Inch Diamerer; aboue this
HIole Fhere arC IO BC APUCK ENO OE ChrCC C On-
centrick Circles. More this Paper uxon ttie
GlaIS, Fil rou sec on the Plane That receires
che reflected Lighe, thac the bright Spor is ex
actly in che middle of che ocher Fainter Listc
round il.
This also one may meature by a Pair oF Com-
RaYS FAEare (collateral, OF) OuE OF the Glases passes, havins, co rhac end, Dighely Ax d che Pa-
AXIS. Bur che different Refrancibility ot diste-
rene Rays ill For ever hinder us From pertectine
Opticks by Glases, cicher Spherick, Or oF any
octer Fisures Whatloerer: And untess we can
correct the Frrors that arise from hence, all our
Labour is lost in orter Corrections.
Nor indeed is it porsible, by whacerer Figures
EO render the ApPCarance OF the Collateral PAFES
per co che Clals, thac e mar more nicely de
termine whecher chis bright Spor be exactly in
chemidale. This cheretore beins caretully ad-
justed, by senely Didins che Paper on che Cla(S
(it ic be requisire) wre are, without the leact
alterins this erue Position ot the Paper, t0 Ax ic
more tirmly ro the GlaIS; and lavins ic thus on
a TablC, let us marke on the Cla(S (By the Point
of an Object (0 distinct as the Direct; For the oF a Diamond) chree Poines in one ot the C ir-
very NaturaL Fre does it nOF: And cheretore e cumterences concentrick ro che round HTole in
are Forced ro apply ic successireY, directly Be-
Tore che ParrS oF any Object ve desien +
vieW.
T0 lnon mbecher Oprick. Clattes be truly Cen
rered, or not.
Fiest Way.
Candle; For where those euo Imases unite, ot
the Paper; and sticking a (mall piece ot Ce
mene on te Olals, about che midale ot che
round FTole, by means oE che chree marted
Poines let us Aind the exact Centre ot chis round
Hlole: Then uncorering che wtole Cta(S, (ex
cepe omy che Cemenc in wtich che Centre is
marke d) vich a Diamond Poinced Compals let us
Arike as larse a Circle on ihe Cilals as iis Breadch
Will bear; then round the Ctals accordine ro rtiis
Circle, and ris as exactly centred as the Sense
can judee.
FToldins che Classes al d due VITance HO
the Fre, obserre the rwo resected Imases oF 2
coalesce, chere is the true Centre of the Claß
And it ehis De in the midale or central POinE0
the ClassS Breadch, the Clals is truly centered.
For eryns the Rezularies and Goodness of an b
ject. ClalS, 1othe greatest Lxactnest,
On 2 Paper strike truo Concentrick Circles.
one whole Diameter is the lame wichthie Breadct
OF the Object. Ctals, e’orher, oF halF rhac Dia-
meter: This invard Circumterence divide into
six equal parts, by che Hnoun wax ot applyine
makeins six sine sinall Holes cherein with 2
ich ehis Paper, and chen expolins it tothe Suns
We are ro receire the Rays chat pals chrougtr
Proachins chis Plane trom or ro the Cilals, We
oriohtest Spot iS EO BC DIM into the smallest Phall find Whether che Rays thac pass chrouoh
Compalo cac ic can. CL rial will mabie alt chis) chese six Holes unice: exactis rovethex ac ans
Distance
A Secona. N a) IS,
By presentino che Glals besore the Sun, and
rallel ro irs Surtace, and at a proper Distance; the Radius six rimes in che Circumference, and
For rhen roul percetre cuo lous d lis le
visorous, wichin anocher more faint and larse
Then by a due Posture oF the Ctass (found by
round as possible, and aE a PFOPeF DITaNCCHOIM From rhe CtaIs; and by wich- drawins or ap.
makins LL TCHCCLCHC LGMCOI a PTaI MSIs Pa
Aected, onc smaller, bur much more strons and Nccdle. Ler us corer one side of che Cla(S
TrialS) Both These Lighrs are ro be projected as rhese SX FToles, on a Plane, ae a just Distance
the Wall on ertich cher are reflected; the round