about three foot radius (fuppole a broad Objeft-glafs of a three 
foot Telefcope,) at the diftance of about four or five foot from 
thence, through which alt thofe colours may at once be tranfmit- 
ted, and made by its Refradlion to convene at a further diftance 
of about ten or twelve feet* if at that diftance you intercept this 
light with a fhect of white paper, you will fee the colours convert- 
ed into whitenefs again by being mingtc'd* But it is reqLiifite,thac 
the Prrfme mdLens be placed fteddy, and that the paper, on 
which the colours are caft, be moved to and fro ^ for, by fueh 
motion, you will not only find^ at what diftance the whitenefs is 
moft perfedi:,buc alfo fee,how the colours gradually convene, and 
vanifh into whicenefsj and afterwards having croflid one another 
in that place where they compound Whitenels, are again difBpa- 
ted, and fevered, and in an inverted order retain the fame co- 
lours, which they had before they entered the compoficion. You 
may alfo fee, that, if any of the Colours at the Lens be intercept- 
ed, the Whitenefs will be changed into the other colours. And 
therefore, that the compofition of whitenefs be perfe(a,care muft 
be taken, that none of the colours fall belides the Lens. 
In the annexed defign of this Experiment, ABC exprcfTeth 
the Prifm fet endwife to fight, clofe by the hole F of the window 
E G. Its vertical Angle ACE may conveniently be about 60 
degrees; defigneththe Lens, Its breadth 2| or 3 inches. 
S F one of the ftreight lines, inivhich difForm Rays may be con- 
ceived to flow fucceffively from the Sun* FP,and FR. two of 
thofc Rays unequally refraded, which the Lens makes to converge 
towards Q, and after decuflation to diverge again. And H I the 
paper, at divers diftanccs, on which the colours are projeded : 
which in Ct conftitute Whitenejsy but are ReddLuA Tellom in R,r, and 
f, ^ndBliWMd Purple in P, p^and ^r. 
