any other smooth glassie body, is, in my opinion, onely made by the motions of the Looking-glass, which do both pattern out, and present the figure of an external object in the Glass: But you will say, why do not the motions of other bodies pattern out, and present the figures of external objects, as well as smooth glassie bodies do? I answer, they may pattern out external objects, for any thing I know; but the reason that their figures are not presented to our eyes, lies partly in the presenting subject it self, partly in our sight; for it is observed, that two things are chiefly required in a subject that will present the figure of an external object; first it must be smooth, even and glassie, next it must not be transparent: the first is manifest by experience; for the subject being rough and uneven, will never be able to present such a figure; as for example, A piece of steel rough and unpolished, although it may perhaps pattern out the figure of an external object, yet it will never present its figure, but as soon as it is polished, and made smooth and glassie, the figure is presently perceived. But this is to be observed, that smooth and glassie bodies do not always pattern out exterior objects exactly, but some better, some worse; like as Painters have not all the same ingenuity; neither do all eyes pattern out all objects exactly; which proves that the perception of sight is not made by pressure and reaction, otherwise there would be no difference, but all eyes would see alike. Next I say, it is observed, that the subject which will present the figure of an external object, must not be transparent; the reason is, that the figure of Light being a substance of a piercing and penetrating quality, hath more force on transparent, then on other solid dark bodies, and so disturbs the figure of an external object pattern'd out in a transparent body, and quite over-masters it. But you will say, you have found by experience, that if you hold a burning Candle before a Transparent-glass, although it be in an open Sun-light, yet the figure of light and flame of the Candle will clearly be seen in the Glass. I answer, that it is an other thing with the figure of Candle-light, then of a duskish or dark body; for a Candle-light, though it is not of the same sort as the Suns light, yet it is of the same nature and quality, and therefore the Candle-light doth resist and oppose the light of the Sun, so that it cannot have so much power over it, as over the figures of other bodies patterned out and presented in Transparent-glass. Lastly, I say, that the fault oftentimes lies in the perceptive motions of our sight, which is evident by a plain and Concave-glass; for in a plain Looking-glass, the further you go from it, the more your figure presented in the glass seems to draw backward; and in a Concave-glass, the nearer you go to it, the more seems your figure to come forth: which effects are like as an house or tree appears to