How to make a Glass that shall shew nothing but what you will.
Also a Glass is so framed, that when you look into it, you shall not see your own pi∣cture, but some otherface, that is not seen any where round about. Fasten a plain Glass on a wall upon a plain, set upright perpendicularly, and bow the top of it to the known proportion of the Angle: right against it cut the wall, according as the pro∣portion of some Picture or Image may require, and set it by it, according to a fit distance, and cover it, that the beholder may not see it (and the matter will be the more wonderful) nor can come at it: The Glass at a set place will beat back the Image, that there will be a mutual glance of the visible Object and the sight, by the Looking-glasses: there place your eye; you shall find that place, as I taught you be∣fore. Wherefore the spectator going thither, shall neither see his own face, nor any thing else besides: when he is opposed to it, and comes to the set place, he shall see the Image or the Picture, or some such thing, which he can behold nowhere else. You shall now know