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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 55, page id 1677894601:0065
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s
oF 2 Ray Wrhich tias a mean degree of Retrangibiliey, and
chis sinc is in a giren Proporcion co the equal sines ot
Incidence, those ocher Sines of Retraction will also bc in
siven Proportions coche equal sines ot Incidence. Nou
When che sines of Incidence are equal, ic will appear by
the folloino Experimene that the Sines of Retraction are
in a giren Proportion to one another.
Exper. 15. The Sun Chinins into a dark Chamber
chroueh a licele round hole in che Windor-Buc, lec S re-Fis. 26.
present his round uhice image painced on the opposice
Nall by his direct Ligne, P This oblong coloured Imase
made by retractinq chac Lighe wich a Prilm placed ac che
Windon; and pF, Or 2p2t, or 3P 3t, hisoblone coloured
lmage made by retractins again che lame Lighe sidemays
ich a second Prism placed immediacely atcer che frst in
a crols Policion eo ic, as vas explained in che fitch Fxperi-
menE: thac is eo Par, pt When cheRefraction of the second
Prilm is (malI, 2p 2 F When ies Retraction is greater, and
3P 3t when ic is greatest. For such will be the diversiey
ot che Retractions it che retractins Angle oF che sccond
Prilm be oF various Magnicudes; suppOse OF FIIECCN OF
civener degrees ro makce the Image pi, oF chirey Or
forey comakce the Image 2p 2F, and ot sixer co mate
the lmage 3p 3t. Buc for anc ot solid Class Prilms wich
Angles ot conrenient bignesles, chere mar be Vessels
made ot polistred Places ot Class cemented cogether in the
Form of Prilms and filled wich Wacer. Thelechines beins
thus ordered, I obserred chac alt the Colar Images Or co-
loured Spectrums P P, pt, 2p 2t, 3P 3c did very nearty
converse co che place S on irhich che direct Lighe ot the
Sun Fell and painced his irhice round Image when che
Prisms vere calcen arvar. TheAxis of che Spectrum P I,
chac is the Line drann chrough che middle oF ic Parallel t0
HES