Of jlrange (jlasses.

119

Place all these boards together, that the solid parts may stand altogether, as to makea perfect plain: Then paint your own Picture, or of some other thing upon it s yetby this artifice and great observation, that if the Image be neer the Glass, it mustbe drawn as it were afar off. If you would have it far distant, let the forehead beimmeasurably long, the nose somewhat longer, and the mouth, and the chin, like-wise. The manner how to draw this Form exactly in Tables , I said in aay Opticks.When the Image is now described, fasten the little boards upon a plain Table , thatthe head may be set downwards, and the chin upwards; and place the first Tableafter the second, and the second after the third, till they be all fastned. Hang theTable above a mans height, that no man may fee into it, above the degrees of theTables: and place a Glass over this , distant two foot from the Table, so long lift-ing it up, and putting it down till yon fee the perfect Image. Now when any mancomes neer the Glass to fee his own Image, he (ball fee the Image of some otherthing that appears no where. In the breadth of the Tables you may draw somePicture, lest they should give some occasion to suspect.

Chap. XXI.

How Spett as lei are made.

were very necessary fer the operations already spoken of,

VT’^E fee that Spectacles

* * mm aITa 1 «/-•«'! *«■ I

v v or else lemicuslar Crystals, and without these no wonders can be done. Itremains now to teach you how Spectacles and Looking-glasses are made, that everyman may provide them for his use. In Germany there arc made Glass-balls, whosediameter is a foot long, or there abouts. The Ball is marked with the Emril-stone round, and is so cut into many small circles, and they are brought to Venice.Here with a handle of Wood are they glewedon, byColophonia melted: And ifyou will make Convex Spectacles, you must have a hollow irondish, that is a porti-on of a great Sphære, as you will have your Spectacles more or less Convex ; and thedish must be perfectly polished. But if we seek for Concave Spectacles; let therebe anlron-ball, like to those we (hoot with Gun-powder from the great Brass Ca-non : the superficies whereof is two, or three foot about: Upon the Dl(b, or Ballthere is strewed white-fand, that comes from Vincentia, commonly called Sal dame,*nd with water it is forcibly rubbed between oar hands, and that so long until thesuperficies of that circle (ball receive the Form of the Dish, namely, a Convex fupre-ficies, or else a Concave superficies upon the superficies of the Ball, that it may sicthe superficies of it exactly. When that is done, heat the handle at a soft fire, andtake off the Spectacle from it, and joyn the other side of it to the fame handle withColophonia,and work as you did before, that on both sides it may receive a Con-cave or Convex superficies: then rubbing it over again with the powder of Tripolis,that ir may be exactly polished j when it is perfectly polished , you (ball make itperspicuous thus. They fasten a woollen-doth upon wood; and upon this theysprinkle water of Depart, and powder of Tripolis ; and by rubbing it diligently, you(ball fee it take a perfect Glass. Thus are your great Lenticulars, and Spectaclesmade at Venice.

Chap. XXII.

Hew upon plain Concave and Convex Closes , the fells are laid on and they are banded.

N Ow it remains that I speak of some few things,not to be overpassed of the band-ing of Convex Glasses, and of foiling plain Glasses, and Convex Glasses, thatso I may set down the perfect Science of Looking-glasses. First, for the terminatingof Looking glasses, that arc made of Crystal and Glass, then of other mixtures, andpolifbings, that a knowing Artificer may know, and know how to mike them:For though amongst many things, that (hew the Images of things , as water , some

Jewels, and polished Metal ,do it; yet nothing doth so plainly represent Images,

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