( 44 <* ) 
To {hew that the Colours in this Sptttrum were fi tri- 
ple and homogeneal Lights, I made the following Experi- 
ments. 
Having made an Hole h in the Paper which receiv’d 
the colour’d Speffimm, I fuffer’d the red Light to pais ; 
which being refraded by a fecond Prifm, fell upon ano- 
ther Paper at 7 ", where it appear’d ilill Red whether feen 
with the naked Eye or Prifms of different refrading An- 
gles. To the Eye which faw it thro’ the Prifm V, it ap- 
pear’d indeed lower as at t, but red, round and unchang’d. 
1 made the Experiment upon all the Colours, which by 
this means appear’d to be fimple and homogeneal. See Fig. 
22. Where the fame Letters denote the Lens, Prifm and 
firft Paper. 
Thro’ the fame Lens and Prifm the Speffrum was made 
to fall on a Book ; then thro’ the Prifm F it appear’d un- 
chang’d ; and the Letters in the Book which crofs’d the 
Speffrum, were as diftind as when feen with the naked 
Eye- See Fig. 23. 
N. B. The Axis of the Prifm F ought to be perpendi- 
cular to the long Axis of the Speffrum s m thrown on the 
Book, which will appear as at a p ; and the Prifm in the Po- 
rtion reprefented at /^with its flat Side towards the Nofe: 
for that is the moft convenient Pofition for looking at the 
Spe&rum in thefe Experiments. 
I fufFer d the purple Ray only to pals thro’ the Hole h 
and fall upon a Book at P, the Letters of which appear’d 
at 7 r, and were as diftind thro’ the Prifm when feen 
with the naked Eye : and I had the fame Succefs with all 
the other Rays. See Fig 24. 
But if a Sun-Beam as r comes thro’ the Hole 7 /diredly 
upon the Book at IV, an Eye looking at it thro’ a Prifm 
EXPERIMENT IX. 
