Opticks 1717 - Up

e 29 I
firft ill a ads PoGtion to it, that it might a.gairI
r&a& the beam of the Sun’s Light which came
to it through the firit Prifrn. In the firit Prifrn
this beam was refratted UPWS~S, and in the
fecond meways. And I found that by the H$efsatlion
of thc’kcond Prifnl the breadth of the
Image was not increafcd, but its fuperior part
which in the firii: Priftn MTered the greater
RefracGon and appeared violet and blue, did
again jn the fecond Priiin fuEer 8. greater RefraAion
than its inferior part, which appeared
red and yellow, and this without any Dilatation
of the Image in breadth.
lhjhz~io~~. Let S [in Fz$. p.s.1 reprefent
the Sun, F the hole in the “WmdoWY AI3C the
firfi Priiin, D .H the fecoud Prifm, ‘1’ the round
Image of the Sun made by a direct beam of
Light wheu the Prifms are taken air-ay3 PT
the oblong Image of the Sun made by that beam
paihng through the firit Prifin alone when the
fecond Prifin is taken away, and p t the Image
made by the crofs RefraAions of both Prilixs
together. Now if the Rays which tend towards
the feveral Points of the round ImageY
were dilated and fpread by the Refra&ion c$
.the firit Psih, fo that they ihsuld not any lon-
\ ger go in iingle Lines to fingle Points, but that
,cvery Ray being @lit, fhattered, and changed
from a Linear Ray to a Superficies of Rays diverging
from the Poiuk of Refraction,’ and lying
in the P!.nnc of the Angles of Incidence and
Kefra&ion, they fhould go in thofe Planes to
fo many Lines reaching alrnoik from one end of
the Image PT to the other, and if that Image
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