[F] _See our_ Author's Lect. Optic. Part I. Sect. II. Sec. 29. [G] _This is demonstrated in our_ Author's Lect. Optic. _Part_ I. _Sect._ IV. _Prop._ 37. [H] _How to do this, is shewn in our_ Author's Lect. Optic. _Part_ I. _Sect._ IV. _Prop._ 31. THE FIRST BOOK OF OPTICKS _PART II._ _PROP._ I. THEOR. I. _The Phaenomena of Colours in refracted or reflected Light are not caused by new Modifications of the Light variously impress'd, according to the various Terminations of the Light and Shadow_. The PROOF by Experiments. _Exper._ 1. For if the Sun shine into a very dark Chamber through an oblong hole F, [in _Fig._ 1.] whose breadth is the sixth or eighth part of an Inch, or something less; and his beam FH do afterwards pass first through a very large Prism ABC, distant about 20 Feet from the hole, and parallel to it, and then (with its white part) through an oblong hole H, whose breadth is about the fortieth or sixtieth part of an Inch, and which is made in a black opake Body GI, and placed at the distance of two or three Feet from the Prism, in a parallel Situation both to the Prism and to the former hole, and if this white Light thus transmitted through the hole H, fall afterwards upon a white Paper _pt_, placed after that hole H, at the distance of three or four Feet from it, and there paint the usual Colours of the Prism, suppose red at _t_, yellow at _s_, green at _r_, blue at _q_, and violet at _p_; you may with an Iron Wire, or any such like slender opake Body, whose breadth is about the tenth part of an Inch, by intercepting the Rays at _k_, _l_, _m_, _n_ or _o_, take away any one of the Colours at _t_, _s_, _r_, _q_ or _p_, whilst the other Colours remain upon the Paper as before; or with an Obstacle something bigger you may take away any two, or three, or four Colours together, the rest remaining: So that any one of the Colours as well as violet may become outmost in the Confine of the Shadow towards _p_, and any one of them as well as red may become outmost in the Confine of the Shadow towards _t_, and any one of them may also border upon the Shadow made within the Colours by the Obstacle R intercepting some intermediate part of the Light; and, lastly, any one of them by being left alone, may border upon the Shadow on either hand. All the Colours have themselves indifferently to any Confines of Shadow, and therefore the differences of these Colours from one another, do not arise from the different Confines of Shadow, whereby Light is variously modified, as has hitherto been the Opinion of Philosophers. In trying these things 'tis to be observed, that by how much the holes F and H are narrower, and the Intervals between them and the Prism greater, and the Chamber darker, by so much the better doth the Experiment succeed; provided the Light be not so far diminished, but that the Colours at _pt_ be sufficiently visible. To procure a Prism of solid Glass large