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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 806933011:0349
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IF O V che Distanice olche Object from the Pole
or Verrex of the Class, be caken instead et P
chen will C O berhe Disserence oF O V al CR
and as chac Difference is 10 C R, (0 is the lladius
CV 1OC F che Distance ot the Pinspat locus
Fromche Cenrre ot he sxliete, Wut ihe Citass
is a Sepment.
OF elle, aS CG) 1OO P OF R 9 :: S0 PC 10
V F, ihie Focal Distance fron the Pole ot he CalS.
Nhence Pollos a general Rule For the Foci ot
all Glasses, only accordins 10 Cor. 3. it OV de
excced CR, the Focus is on che lame side oF ine
Olals, a5 is che Cenere oP ihe Sphere. Bur it C B
begreater, chen che Focus is on the opposire Mide O
che Glass; irhence ir will be derermined, wtiertier
che Focus De Leal or tmaginari.
OROLLRAY Vi
Erhat has Been Caid OF one Surtace OF 2 Lens, i5
easily applicable rorhe orher; ratine F, the FOcuS
of the srst Surta ce as an Object, and utins icasO
in rhe Figures For Fmergine Rays; Whereby che
Focus oE borh Surtaces will be determined, 25 in
18
AII which are dravon wich IHC (aME LereTS 1
their respectire Points, only in Pome che PoinE L
Fallins Car distanc, is ro be understood in the Incer-
section oE che Line P F wichche AXis. e
This chus demonstrated in che most disticule Ca-
ses, Will gire all che Rules For the Foci oF Rays
Parallel co che Axis, as likewise For che principal
LOcus, Where che Rays nearest che Axis dounire:
All which Rules are collected in chele followins
Corollaries.
COROLLAEY L
IF OP DC equalto C R, chen che Poins C anc
Care coincident, and che Rays OP alter Retra-
ction, rum on Parallet e0 che Axis.
COROLLARY II
IEche Point C Fall on che Pame Side oF the Aris
asis the Point P, then the Beams aster Retraction
dorend on, cicher Dirergins or Convergins as bc.
Fore: But if ( FaIl on the orher sde the AXIS, 25
in Fis. I. che Divergins Rays are made 10 Con-
verBC bY a COnVCK, OE CC Conversins 10 DiversC
by a Concave Claso.
COROLL ARY VI.
IF OP. do exceed C R, che Focusis in aM C ases
on the same sde OF the CtasS aS IS FHC CCHErC OF
the Sphere C.
Bur contrarimile, IF O P be lels chan C R, the
Focus falls on the orter side ot the Citals berond
che Verrex V.
COROLLREE IV.
An Objeet may be l0 placed, Thatthe AassCAL
the Axis ot a Convex-ClaS, Mail have an Imagina-
ry Focus, erantinierinq Divergins Rays, When chc
mere remore Parrs chereot, Mall make chem COn.)
rergeto 2 real FOcus.