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tire and Adequäte caule of their Colours, is manifest:, becaufe they have noPower to changc or alter the Colours of any fort of Rays incident aparr,but put on all CblcHirs indifferently, with which they are enlightened.

' These things heilig so, it can be no langer di'puted, whetlier there be Co-Jours in the dark, nor whether they be the qualities of the Objects we see, nonor perhaps, whether Light be a Body. For, fince Colours are the Qualitiesot Light, having its Rays for their intire and immediate Subject, how can wethink thole Rays Qualities also, unlels one Quality nuy be the Subject of, andsostain another; which in effect is to ca!i it Subitanee. We fhould notknow Bodies for Subfrances, were it not for their sensible Qualities, and thePrincipal of thole being now found due to something elfe, \vc have as roodRealbn to believe that to bea Substance also.

Belides, Who ever thought any Quality to be a Hetercgeneous Aggre-gate, such as Light is diseovered to be? But to dctermiiie more absoliitelv,what Light is, alter what manner Refracted, and by wh.at Mcdes or Aeti-on s it produceth in our Minds the Phantasras ot Colours, is not so ea Ite :And I fhall not mingle Conlectures with Certdinties.

Reviewing what I have w ritten, 1 lee the diicourfe it (elf will leacl to diversExperiments lulhdent for its ExaminatioriAnd therefore 1 (hall not troublcyou further than to delcribe one of those, which I have already insinuated.

In a darkened Room tnake a Hole in the Shut of a Window, v. hole Di-ameter may convenienti)’ beabouta thirdpavt of an Incb, to admit a conve-nient quantity ot theSun’s Light: And there place a ciear and colourlels Prilii?,to Refract the entring Light tov/ards the further part of the Room, which, aslsaid, will thereby be diftuled into an Oblong Coloured Image. Then placea Lens of about ? foot Radius v 'soppose a broad Object Glals of a three footTelefcope,) at the distance of about four or live foot front thence, throughwhich all those Colours may atonce be tranfmitted, and made by its Refracti-on to convene at a further distance of about i o or I z feet. If at that distanceyou intercept this light with a theet of white Paper, you will sec the Coloursconverted into Whiteneß again hy being mingled. But it is requisite, that thePrilm and Lens be placed iteddy, and that the Paper, on which the Coloursare cast, be moved to and sio; for by such motion you will not only find,at what distance the Whiteneß is most perfect, but also fee, how fne Cc-lours gradually convene, and vanilh into Whiteneß, and afterwards havingcrofled one another in that place where they compound Whiteneß, are againdistipated, and severed, and in an inverted order retain the fame Colours,which they had betöre they entred the composition. You may also lee, thatif any of the Colours at the Lens be interceptcd, the Whitenels willbe chang-ed into the other Colours. And therefore, that the composition of Whitenelsbe perfect, carc must betaken, that none of the Colours fall besides the Lens.Thus, in the designof this Experiment, ABC, expreffeth the Prifm set end-F‘j. 7'. wise to fight, dose by the Hole F, of the Window EG. Its Vertical AngleACB, may conveniently be about 6o degrees: MN, designeth the Lens. Itsbreadth if or three inches. 8F, one ofthe StraightLines, in which Difform{{/ijs may be conceived to flow socceflively from the Sun. F P, and F R, two

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