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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 12, page id 1677894601:0184
# Original at the GWLB: https://digitale-sammlungen.gwlb.de/resolve?id=1677894601&page=184
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In the erro Rest Columnsarc expressed the obliquities
ot the incident and emergent rays to the plate ot the
Air, that is, their ansles of incidence and retraction. In
the third Column the Diameter ot any coloured Rine
at thole obliquities is expresed in parts, ot irtrich ten
conscitute that Diameter irhen the rurs arc perpendicu-
lar. And in the Tourth Column the thickness ot the AIr
at the circumterence ot that Rins is expressed in parts
OE wrhich al(o ten constiture that thicknels irhren the rayS
are perpendicular.
And From these meatures I Ecem to sather this Rule:
That thethickness oF the Air is proportional tothe sc-
Cant OF an ansle, wrhole Sine is a certain mean prOPOT-
tional betreen the Sines ot incidence and retraction.
And that mean proportional, (0 tar a5 by thele meatures
lcan decermine iE, IS the tirst ot an hundred and six
arichmetical inean proportionals betreen thole Sines
counted fiom the sine ot retraction irtren the retra
ction is made out of the Cla(s into the plate oF RIT, Or
From the Sine ot incidence wrten the retraction is
made out ot the plate ot Air into the Cila(5.
OBS. VIII.
The dark Spot in the middle of the Rinos inerealed
also by the obliquation of the Lye, althoush almost in-
Censibly. But it instead ofthe Object-Cilaces the Prisms
evere made use otq its increase as more manifest irhen
viemed (0 obliquely that no Colours appeared about it.
Itras least irhen the rays rere incident most obliquely
on the interjacent Air, and as the obliguier decrealed
it increaled more and more until the coloured RingS ap-
Dearec,