GH shall be oblique to the refracted Rays CHK and GI; and the angle GHC shall be an acute, and so much the more acute by how much the greater the refraction be, then which nothing is more evident, for the sign of the inclination is to the sign of refraction as GF to TC the distance between the point C and the perpendicular from G on CK, which being as four to three, HC being longer then GF is longer also then TC, therefore the angle GHC is less than GTC.  So that henceforth the parts of the pulses GH and IK are mov’d ascew, or cut the Rays at oblique angles.

It is not my business in this place to set down the reasons why this or that body should impede the Rays more, others less:  as why Water should transmit the Rays more easily, though more weakly than air.  Onely thus much in general I shall hint, that I suppose the medium MMM to have less of the transparent undulating subtile matter, and that matter to be less implicated by it, whereas LLL 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 mediu; 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 ABC in the second Figure to represent a large Chimical Glass-body about two foot long, filled with very fair Water as high as AB, 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 ab, through which the Sun-beams are suffer’d to pass into the Water, and are thereby refracted to cdef, 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, cd shall exhibit a Scarlet, which toward d is diluted into a Yellow; this is the refraction of the Ray, ik, which comes from the underside of the Sun; and the Ray ef shall appear