320 Of Light and Colours.

or Violet Rays; and so the Image will becoloured and confused in every Point be-tween

Platexxxvi.Fig. II

with the Sines of Refraction of the most, mean, anleast refrangible Rays, will stand as follows.

CThe most refrangible Rays FU>j as 8047 to 5112.

The Sineof Incidence J The mean refrangible Rays E”*is to the Sine of j as 8047 to 5188. n

j The least refrangible Rays G VfI as 8047 to 5262.

22. I have hitherto considered the Refraction nEout of Air into Glass, after the common Way.

as Sir Isaac Newton has proceeded in a contrarythod, and stated the Proportions of the Sines of R e 'fraction (as they are out vf Glass into Air) to the cofl 1 'mon Sine of Incidence in Qlafs, I shall for the fut uf ^follow his Steps ; and therefore supposing a Beam 0common Light within the Prism, as D E, shall consider its Refraction into the Air at the Side B C in'^Point E. The common Sine of the Angle of IncidentKED or IEL = 31 9 15', was found to be 518“’and the Angle PER z: i° o' 37", the fame as beso r fAlso the Angle of the mean refrangible Rays T Ebeing 53 0 35', we have the Angle of the least ^frangible Rays REL = 53 4' 58", and the Anglffthe most refrangible Rays PEL — 54 0 5' os'. * ^Sines of these Angles are 7995 and 8099 ; the Sin eIncidence, therefore, and of Refraction into Air, in * jleast and most refrangible Rays, are in the least roU 11Numbers as 53 to 77 and 78.

23. Now if you subduct the common Sine of ln c ‘donee 50 from the Sines of Refraction 77 and 78, *■Remainders 27 and 28 shew, that in small Refract^ 0 / 1 Jthe Refractions of the least refrangible Rays is to f jof the most refrangible as 27 to 28 very nearly;that the Difference of the Refractions of the leastmost refrangible Rays is about the 27I Part of the stfraction of the mean refrangible Rays.