Opticks 1717 - Up

fuch 1vi11 be the dikrfity o? the RefiaAio~~s if
the refraAing Angle of the fecond Prifin be of
various magnitudes ; fuppofe of fifteen or tvkenty
Degsecs to make the Image p t, of thirty or
forty to make the Image 2~ 2 t, and of fixty to
make the Image 3p j f. But for want of folid.
Glafs Prifms with Aligles of convenient bigncl4ks,
there may bc VeiTels made of poliflled
Plates of Glafs cemented together in the form
of Prifins and filled with XVater. T’hefe things
being thus ordered, P obfervcd that all the ioiar
Images or colourcd Spe&rums I? ‘I’, p L, 2~
2 I', 3 p 3 t did very nearly converge to the
place S ou which the dire& Lighr of the Suli
fell and painted. his white round Image when
the I’rifms were taken away. The h;:is of the
SpeArurn P ‘I’, that is the Line drawu through
the middle of it parallel to ,its re&ilinear Sides,
did wheu produced pafs exaAly through the
middle of that white round hnage S. And when
the Refraktion of the fecond $W’m vkts equal
to the Refraction of the fir& the refraAing Angles
of them both being about 60
Axis of the SpAruin 3 p 3 t ma
fsaAion, did when produced. pa
the middle of the fame white round Image S.
But when~ the RefraAion of the fecond Prifin
was lefs rhan that of the firit, the produced
Axes of the SpeArurns up or 2 z ,z p made by
that Refra&ion did cut the ,produced Axis of
rhe SpeArum ‘37 $ iu the points FB and n, a httie
be ond the center of that white round. B-
mage s ‘* Whence the proportion of the Line
3 t T’ to the Line 3pP 15721.5 a little greater thaln
Fa
the