C *35 )

ofthose Rays unequally Refracted, which the Lens makes to Converge towardsQ, and aftcr Decustation to Diverge again. And HI, the Paper, at divers di-ances, on which the Colours aie projected: Which in Q, constitute Whiteneß,but are Red and Yellow in R, r, and j, andBlue and Purple in P, />, and ir.

If you proceed further to try the impostibility cf Changing any Üncompound-ed Colour (which I have afferted in the third and thirtccnth Propositions) ’tisrequisite that the Room be m.ide very dark, least any scattering light, mix-ing with the Colour, disturb and allay it, and render it Compound, contraryto the design of the Experiment. ’Tis also requisite, thatthere be a perfectorSeparation of the Colours, thun, afrer the mannt-r above destribed, can bemade by the Refraction of one fingst Prism, and how to malte stich furtherSeparatioris, will (carce be difficult to them, that consider the distovered LawsofRefractions. Butiftryal Ihallbe made with Colours not throughly stparated,theremustbe allowcd changes proportionableto the mixture. Thus if "Com-pound Yellow Light fall upon Kiue Bist, the Bist will not appe.tr pcrfcctlyYellow, but rather Green 3 bccattst there arc in the Yellow mixture manyRays indued with Green, and Green bcing Icß remote front the ustial BlueCo-lourof Bist than Yellow, is the more copiously restected by it.

In like manner, if any one of the Prisinatick Colours, sttppost Red, beinterceptcd, on delign to try theasterted irttpoii.bility of rcprodttcing that Co-lour out of the others which are pretermitted, ’tis necestary, cither- that theColours bc very well p-arted Lcfore the Red be inierceptcd', or that togetherwith the Red the neighbouring Colours, into which any Red is secretly dil-perstd, sthat is, the Yellow, and perhaps Green too) bc interceptcd 3 or eist,that allowance be made for the emcrging of so much Red out of the Yellow-Green, as may poilibly have been diftused, and statteringly blended in those'Colours. And ir these things be observed, the new production of Red, orany interceptcd Colour, will be found impostible.

II. 1. Tocontract the Beams of the Sun without the Mole ofthc Window',and to place ihePristn betwecn the Focus of the Lens and the Hole.

i. To cover over both ends of the Prism with Paper at stveral distances <« nUnon tofrom the middle ; or wüth moveable Rings, to ste, how that will vary ör dt- th ‘ s Theor J-vide the Length of the Figurc. ‘ "• 3 > / • 4 °;?-

3. To move the Prism so, as the End may turn about, the Middle beingSteddy.

4. To move the Prifrn by sttoving it, till first the one fide, then the mid-dle, then the other fide paß over the Hole, oblerving the fame Parallelifin.

i. I sttppost the design of the Prcprfcr of thest Experiments is, to have obfirvationj ontheir events expressed, with soch observati >ns as may geettr concerning rhem. ^Newton* 1Touching the firfl, I have observed, that the Solar Image falüng oh a Paper n. 83. p. 40V0.placed at the Focus of the Lens, was by the interpofed Prism drawn out inlength proportional to the Prifm’s Refraction or distance from that Focus. Andthe chief obfervable here, which 1 remember, was, that the Streight Edges ofthe Oblong Image were distincter than they would have been without the-Lens. Con-