_Fig. 7._ Shews the Effect of the Lens, or double Convex Glass, in gathering parallel Rays, as G L, H M, A B, I N, K O, _&c._ towards a Point, as D; because, as in the Case of the Prism above, the Refraction _to_ the perpendicular in the Entrance, and _from_ it in the Exit of those Rays, do still, by the different Position of that Perpendicular, conspire to unite the same Rays. _Fig. 8._ Shews the contrary Effect of the double Concave Glass, in scattering the parallel Rays; and that exactly on the like Account; and so this needs no new Explication. _Fig. 9._ Shews the Reason why a Lens, or double Convex, shews a near Object at Q, as more remote at _q_, because it refracts it so that the Rays from the same Point meet more backward than before: And why it shews the same Object larger also: Which must needs be, because every Point in the Object appearing so much more backward, and yet in the same apparent Angle, its Length and Breadth must every where be proportionably enlarg'd. _Fig. 10._ Shews how such a Lens inverts Objects, as A, B, _b a_, which it does on Account of the Intersection of the Rays from each Point, in or near the Lens it self: Which necessarily infers such an Alteration: just as the Images of all Objects are in the Eye in an inverted Position, on the like Account. _Fig. 11._ Shews how a Lens does so refract the Rays from every Point of an Object, that is in its Focus C, and B, and A, that the Rays from each of those Points do become parallel afterward; and also how parallel Rays of different Positions are gather'd in that Focus. _Fig. 12._ Is the Nature of direct Vision by the Eye, in some Conformity to the 10th Figure: only in this Case the Crystalline Humour is the Lens. _Fig. 13._ Is the Case of a Concavo-convex Glass, with its parallel Surfaces, as in _Fig. 1_. [[Plate III. ― Sutton Nicholls sculp:]] OPTICKS. 9 An Explication of the Third PLATE. Figure 1. Is a Telescope, with two Convex Glasses, the one towards the Object and the Segments of a great Sphere, the other near the Eye, the Segments of a small Sphere _g h i_, and they are to be so placed that the distinct Base or Image may, by the Collection of the Rays, be in the common Focus of both the Glasses _f e d_. By these two Glasses the parallel Rays, or those nearly so, as proceeding from the same Point of the Object A B C, (which is to be suppos'd considerably remote) are made to meet in the intermediate Image _f e d_, at _f_, and _e_, and _d_; and again at the Bottom of the Eye, at _r_, and _s_, and _t_; but in an erect Position; and therefore so as to shew the Object inverted.