( 44 ° ) 
come into the Room, which I intercepted with a Prifm at 
the Diftance of j Inches from the Hole ; and after its 
Refraction in palling thro’ the Prilm, I receiv’d it upon a 
Sheet of white Paper, where it was colour’d, making an 
oblong Image of the Sun or Spefirum of about 9 Inches in 
length and 1 in breadth, which Breadth was nearly equal 
to the Diameter of the round Image of the Sun received 
upon a Paper at the fame Diftance from the Hole, which 
here was 1 8 Foot. Or if the Sun be too high, a Looking- 
Glafs being put in the room of the Prifm will throw a 
white round Spetfrum upon the Paper, which held at the 
faid Diftance of 1 8 Foot, will have its Diameter equal to 
the Breadth of the colour’d Speflrum. ./ 
The Colours of the Spetlrum were thefe ; Red, Orange, 
Yellow, Green, Blue, Purple and Violet, tho’ the Vio- 
let was fo faint in this as to be fcarce perceivable. Sec 
Fig. 9. . ... . 
AT. B. The Axis of the Prifm in this, and all the other, 
Experiments hereafter mention’d mu ft be perpendicular to. 
the Ray that falls on it ; and the Plane into which the Ray 
enters muft be held in fuch a Pofition.that the A ngle which 
fuch a Ray makes with that Plane when it enters, 
maybe equal to tjie Angle made by the middle Line of 
thofe Rays which emerge after RefraCtion, on the other 
Side of the refraCting Angle of the Prifm, with the Plane 
out of which they emerge. That is L BDG—U AEH 
If the Plane A C, on which the Sun-Beam falls, be tur- 
ned nearer to a perpendicular to the Sun Beam than be- 
fore, the Spetfrum will be much longer .* if it be more in- 1 
din’d to the faid Beam, the SpeBrum will be fhorter, and 
in both Cafes lefs diftinCt. See the SpeBr urn D A* and the 
Spetfrum d e in Fig 1 o. and 1 1 . where H, b, reprefents the 
Hole in the Window Shut in each Cafe ;AC, ac the 
Plane of the Prifm on which the Rays enter ; BCy.bc that 
out of which they emerge; P, p the perpendicular, and 
C, c the refracting Angle. If 
