y 
the Infection , Refection , and Colours of Light. 241 
received on a screen with a hole in the middle, through which 
a small part of it passed, and falling on the reflector placed 
behind, was formed by it into images, after the manner of 
the first experiment, each having in regular order the seven 
prismatic colours. One of the brightest and most distinct I 
let pass through a hole in a second screen, and it fell on the 
chart. I then caused an assistant to intercept the red rays 
between the first prism and the lens, and immediately the red 
part of the image vanished ; and when the violet was inter- 
cepted, the violet of the image vanished ; and if the green was 
intercepted, the green was wanting in the image. In short, 
whatever colours were stopped, the same were missing in the 
image. In fig. 6 , the rays passing through the hole C of the 
window AB, are refracted by the prism PMN, and separated 
into DV, DG, and DR, violet, green, and red ; which being 
collected into a focus F by the lens L, are there again re- 
fracted by a prism P'M'N', and formed into a white beam 
abmn, part of which is intercepted by the screen SS', and part 
passes through the hole h, as Z>H to H on the chart XYZW, 
and part is reflected by the body oq into a set of images which 
are received on a screen TU, and one of them, rgv, let pass 
to WXYZ ; but when an obstacle E stops DR, r the red va- 
nishes ; and if DG be stopped, g the green vanishes ; and if 
DV be stopped, v disappears. Lastly, if DR and DG be stop- 
ped, g and r vanish. 
Obs. 6 . Having produced a set of bright images, I let one 
pass through the desk described in the third experiment, and 
received it on a small lens i inch broad, to collect them into 
a focus, which I received on the chart, by moving it a little on 
its hinge ; and by all the observations I could make, and all the 
mdccxcvi. I i 
