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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 6, page id 1677894601:0016
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In like manner, if there bc 2 Prism oF Glals (hat is a
Class bounded rich evo Pqual and Parallel Triangular
ends, and chrec plane and vell polithed Sides, which meet
in chrec Parallel Lines runnins trom che chrec Anoles ot
one end co the chree Angles ot che ocher end) and it che
Retraction oF che Lighe in pallins crols chis Prilm be desi-
red: TeE ACB represent a Plane curtinq chis Prilm eran
rersly co ies chree Parallel lines or edges there uhere the
Liphic passech chrough ic, and lec dF. bc che Ray inci-
dene upon che first side oF the Prilm A C Where the LixhE
gocs inco che Olals; And by purtins che Proportion ot
che sine ot Incidence eo che sinc ot Retraction a5 17 +0
12 End F F che first retracted Ray. Then calcinq chis Ray
For che Incident Ray upon the sccond side oF che Cla(S B C
irhere che Liohe goes ouE, find che next retracted RaY FC
br purtins che Proportion ot che sine ot Incidence to che
Sine oF Retraction a5 11 +0 17. For it che sinc ot Inci-
denCe OHE OF Rir into Glass bC co ehe sine ot Retraction
25 17 20 1I, che Sine oF Incidence out ot Gla(s intO Rir
must on the contrary be co che sine of Retraction a5 11
eo 17, by che chird Ariom.
Much after che Pame manner, iF A C B D reprelent a
Class spherically Conrex on boch sides Culually called a
Tens, such as is a Burming-glals, or Spectacle-slals, Or an
Object. olals ot a Telelcope) and ic be required to know
hoir Lighe Falling uxon ic trom aur lucid poine 2 Phal
be retracted, lec M reprelent a Ray Fallins uxon any
point MI oF ies first spherical Surtace ACB, and by crectino
a Perpendicular to the Clals at che poine MI, find ehe Airst
retracred Ray M N by che Proportion oL che Sines 17
EOII. Let chac Ray in goins out ot che Clals be inci-
dene uxon N, and chen find che second retracted R ay N g
by che Proportion oF che Sines 1I +0 17. And atter che
Tame
Fig. 2.