( 445 ) 
EXPERIMENT VIII. 
Having made a Hole in the Window-Shut z inches 
wide {Fig. zi.J I applied to it a Tin Plate, which Hiding 
up and down hid all this Hole in the Wood, and only 
tranfmitted a fmall Beam thro’ it's own Hole H , whole 
Diameter was = -< Inch. This Beam, by means of the 
Looking Glafs L, plac’d on the Board of the Window 
X W, I refleded horizontally to the other end of the 
Room. But to corred the Irregularity of the Reflection 
of the Looking-Glafs, I made ufe of the Frame of Pad- 
Board Pp, which had an Hole in it h of t s Inch likewife .* 
and placing it at Pp I fuffer’d lome of the refleded Beams 
to pafs thro’ it, fo as to fall upon the Lens FF (convex on 
both Sides, and ground to a Radius of 4^ Feet) at the 
Diftance of 9 Feet, fo that the Image of the Hole h was 
projeded to/ on the other Side of the Gials, at the Di- 
dance of 9 Feet more. Juft behind the Lens, which by 
a Screw in the Stand S might be rais’d or let down, fo as 
always to receive the Beam along its Axis, I plac’d a Prifm 
A (upright on one of its Ends and eafily moveable about 
its Axis, by reafon of its Wire turning freely in an Holein 
the (olid piece of Wood T, which flood on another Stand 
behind the Lens) as near as I cou’d to the Lens E F, lo 
that the Image of h inftead of being round, white, and 
projeded to / was call fidewife on a white Paper ftretch’d 
on aFrame, and appear’d colour’d, and 30 or 40 timesits 
Breadth, as at M N. The Colours in this Cafe were very 
vivid and well feparated. only the Violec had fome pale 
Light darting from its End, upon account of lome Veins 
in the Prifm A , and the Light not coming diredly from 
the Sun, but refleded ; which ought not to have been, if the 
Sun had been low enough to have thrown the Kays a; 
good way into the Room without the Help of a Looking 
Giafs, To? 
