Mag i g k. Doo^ 1 j.

Natural

Chap. XII.

Haw we may fee in a Chamber things that are net.

1 Thought this an Artifice not to be despised: for we may in any Chamber, isaman look in, see those things which were never there ; and there is no man sowitty that will think he is mistaken: Wherefore to describe the matter, Let there bea Chamber whereinto no other light comes , unless by the door or window wherethe spectator look* in : let the whole window or part os it be of Glass, as we use todo to keep out the cold ; but let one part be polistied, that there may be a Looking-glass on both sides, whence the spectator must look in ; for the rest do nothing. LetPictures be set over against this window, Marble statues , and such-like ; for whatis without will seem to be within , and what is behind the spectators back, he willthink to be in the middle of the House, as far from the Glass inward > as they standfrom it outwardly , and so clearly and certainly, that he will think he sees nothingbut truth. But lest the skill should be known, let the part be made so where theOrnament is, that the spectator may not see it, as above his head, that a pavementmay come between above bis head: and if an ingenious man do this, it is impossiblethat he should suppose that he'is deceived.

Cm a p. XIII.

Of the tf er at ions of a Crystal Pillar.

N Or shall the operations of a Crystal Pillar go unspoken of, for in it there aresome speculations not to be despised. First,

Te kindle fire with a Cryftal 'Pillar ,

by opposing it to the Sun, it will kindle fire behind it about the circumference: oft-times left above the Chamber , when the Sun shined, it burnt the Blankets. Theythat will at set hours and places burn the enemies camps , if it be laid upon fuel forfire, it will certainly kindle ir. We may also

tVith a.Cryfial Pillar, mak* an Image hang in the Aire.

It will strew the Image hanging in the Air, both before and behind. Let the Objectbe behind the Pillar, let the Pillar be between that and the eye, the Image will ap-pear outwardly hanging in the Air, above the Pillar, parted every where from thePillar, clearly and perspicuously - and if the visible Object be between the eye andthe Pillar, the Image will appear behind the Pillar, as I said. If it be a very visibleObject, as fire or a candle, the matter is seen more clearly without any difficulty Igave the reasons in ray Optick?. We may also

In a fryfial Pillar fee many %ain-bows.

Mike a solid Pillar in a Glass furnace, so great as a Walnut, and let it be made roundonely by the fire, as the manner is, as Glafs-naakcrs use to do, that without any helpof the wheel,»he outward superficies may be most polite: where the Iron touched ir,there leave a Pedestal!. It is no matter for pure Glass, for impure is best t place thisupon your eye, and a burning candle over against it ; the light refracted by bladderswill ffiew infinite Bain bows, and all the light will seem Golden-colour’d, that no-thing can be more pleasant to behold.

CHAP*