much in general I shall hint, that I suppose the medium M M M to have less of the transparent undulating subtile matter, and that matter to be less implicated by it, whereas L L L I suppose to contain a greater quantity of the fluid undulating substance, and this to be more implicated with the particles of that medium.
But to proceed, the same kind of obliquity of the Pulses and Rays will happen also when the refraction is made out of a more easie into a more difficult mediū; as by the calculations of GQ & CSR which are refracted from the perpendicular. In both which calculations 'tis obvious to observe, that always that part of the Ray towards which the refraction is made has the end of the orbicular pulse precedent to that of the other side. And always, the oftner the refraction is made the same way, Or the greater the single refraction is, the more is this unequal progress. So that having found this odd propriety to be an inseparable concomitant of a refracted Ray, not streightned by a contrary refraction, we will next examine the refractions of the Sun-beams, as they are suffer'd onely to pass through a small passage, obliquely out of a more difficult, into a more easie medium.
Let us suppose therefore A B C in the second Figure to represent a large Chimical Glass-body about two foot long, filled with very fair Water as high as A B, and inclin'd in a convenient posture with B towards the Sun: Let us further suppose the top of it to be cover'd with an opacous body, all but the hole a b, through which the Sun-beams are suffer'd to pass into the Water, and are thereby refracted to c d e f, against which part, if a Paper be expanded on the outside, there will appear all the colours of the Rain-bow, that is, there will be generated the two principal colours, Scarlet and Blue, and all the intermediate ones which arise from the composition and dilutings of these two, that is, c d shall exhibit a Scarlet, which toward d is diluted into a Yellow; this is the refraction of the Ray, i k, which comes from the underside of the Sun; and the Ray e f shall appear of a deep Blue, which is gradually towards e diluted into a pale Watchet-blue. Between d and e the two diluted colours, Blue and Yellow are mixt and compounded into a Green; and this I imagine to be the reason why Green is so acceptable a colour to the eye, and that either of the two extremes are, if intense, rather a little offensive, namely, the being plac'd in the middle between the two extremes, and compounded out of both those, diluted also, or somewhat qualifi'd, for the composition, arising from the mixture of the two extremes undiluted, makes a Purple, which though it be a lovely colour, and pretty acceptable to the eye, yet is it nothing comparable to the ravishing pleasure with which a curious and well tempered Green affects the eye. If removing the Paper, the eye be plac'd against c d, it will perceive the lower side of the Sun (or a Candle at night which is much better, because it offends not the eye, and is more easily manageable) to be of a deep Red, and if against e f it will perceive the upper part of the luminous body to be of a deep Blue; and these colours will appear deeper and deeper, according as the Rays from the luminous body fall more obliquely on the surface of the Water, and thereby suffer a greater refraction, and the
