_Fig. 4._ Shews the Reason why the same or equal Object, as A B, C D, E F, appears larger when it is nearer, and smaller when farther off: _viz._ on account of the Inequality of the Angles A G B, or M G N, and C G D, or K G L, and E G F or H G I, and the consequent Inequality of the Pictures made by the Rays at the Bottom of the Eye.
_Fig. 5._ Shews the Reason why a Convex Looking-Glass, as A E F B, exhibits Object C D by the Image _c d_, both nearer to the Glass, and lesser than it self; but still in an erect Posture. All depending only on the different Bend of the Circle between E and its lower Point, between F and its upper Point; which cannot make the Angles of Reflection or Inclination equal, as they must needs be in all such Reflections, without making the Vertices of the Angles, as _c_ and _d_, nearer the Glass than C and D: And so the apparent Picture or Diameter _c d_ lesser than that of the Object C D, though without any Inversion.
_Fig. 6._ Shews the Reason why a Concave Glass, as A E F B, exhibits an Object plac'd nearer the Glass than the Center, as C D by the Image _c d_, remoter from the Glass, and larger than it self, _viz._ for Reasons just contrary to those under the fifth Figure foregoing.
_Fig. 7._ Shews the Reason why a Concave Glass, as C D E F, exhibits an Object, if it be plac'd remoter than the Center, as A B, inverted, and at different Distances between the Eye and the Glass; according to the Length or Shortness of its own Distance, as B C or A D, _viz._ Because the Rays from the same Point still cross one another, as at G and H, before they fall upon the Eye; and so by forming an inverted Image make it impossible for the Eye to see the Object in any other Position than that the Image has; which Image indeed it self is the only proper Object of the Eye, in all such Cases whatsoever.
_Fig. 8._ Is a Picture in Confusion; but rectified by a Convex Cylinder, and thereby brought into exact Order again.
_Fig. 9._ Represents an Image in a Cylindrical Concave Surface, when the Eye is in a Plain perpendicular to its Axis; so that lengthways it is as a Plain, and breadthways as a Concave _Speculum_: Which therefore makes the Picture longer, but not wider. The contrary will happen in a Convex _Speculum_, which will make it shorter but not narrower, for the like Reason.