Opticks 1717 - Up

-4
fubdur9ed from the Sines of kzfra&ionY ~~1x
the ‘Esceih will ‘be .27, 27G, 27+, 27-f, 27+9
275 27f, 28. Suppofe noti that the Sine, ,of
Incidence of the leafi refiangibk Rays be to
their Sine of Refrafiion out of Rain-water into~ir
as ‘3 to 4, and fay as I the difference of
thofe Sines is to 3 the Sine of Incidence, fo is
27 the le& of the ExceiEs above-mentioned
to a fourth number 81 ; and 81 will be the
common Sine of Incidence out of dairy-water
into Air, to which Sine if you add al1 the a-’
bovernentioned ExceiTes you will have the deiired
Sines of the RefraAions 108,' 10%~ 1083~
108+, I&, IO&, IOQ, Icy.
By the latter Theorem the Refrafiion out of
one. IYkdiutn itito another is gathered as often
as you have the RefktAions out of them both
into any third M’kdium. As ,if the Sine of Incidence
of an$Ray out of Glafs into Air be to
its Sille of RefraCtion, as 20 to 3 I, and the Siqe
of Incidence of the f~mc Ray out of Air into
Water, be to its Sine of Refr&ion as 4 to 3 ;
the Sine of Incidence of that Ra out of Glafs
illto Water will be to its Sine o fy Refratiion as
7x1 to 31 and 4 to 3 jointly, that is, as the Fa-
&um .of 20 and 4.to the FaAum of 3 I aqd 3 $.
or as 80 to 93.
And thefe Theorems being admitted into Qpticks,
thel:e would be fcope enough of handling
that Science voluminoufly after a newman-
nes ; not only byteachin thofe things which
tend to the perfection o f Viiion , but alfo by
determining ~.riiathematically all l