( 6l2 ) 
the Rays from the Candle R, patted through the lower 
Prifm, and falling upon a Paper at R, made a reddifh 
Spot ; but when 1 fqueezed them very hard, die Spot 
became much wider, white in the Middle, and only- 
tinged with Red about the Edges : At the fame Time 
the Eye faw a black Spot in the Image of the Candle 
at k ; and a Stander-by looking obliquely at the 
Place I (where the Glattes touched) faw, as it were, a 
little Hole through the Prifms as big as the Spot k. 
But if the Prifms be prefled together but gently, then 
all the other Phenomena difappear, except the firft 
little Spot at R, as in Fig. n. 
When the Candle is feen by Refle&ion from the 
lower Surface of a Prifin, as in the 7th, 9th and 
10th Figures, the Rays pafs quite through that Sur- 
face, and are turned up again by the Attra&ion 
of it in Curve Lines fo as to re-enter the Prifm, 
and then (going out again through the Surface A C) 
go up to the Eye at E. In this Cafe the moft refran- 
gible Rays, being the moft eafily infleded, make the 
leaft Curves, whofe Vertices' are nearer the Glafs than 
thofe of the greater Curves made by the leaft refrangible 
Rays. This is proved by Experiment 6 , where the 
under Prifm only attrads down from the Refledion of 
the upper Prifm, the Red making Rays as in Fig. u. 
where the Plate of Air between the Prifms is of fome 
fmall Thicknefs. But when the Prifms, whofe Sur- 
faces are a little convex, are preffed hard together, the 
lower Prifm is near enough to attrad Rays of a great 
Degree of Refrangibility ; and therefore the Spot then 
becomes white in the Middle } and only red about the 
Edges, which are produced by fuch Parts of the lower 
Prifm as are not fo near the upper Prifm. 
There 
