OF GLASSES FOR OPTICAL PURPOSES. 41 



and so grounde by hande, vntill that yt ys bothe 

 smoothe and allso thynne, by the edges, or sydes, 

 but thickest in the middle. And then yt ys the 

 quality or property of the Glasse that ys cleare, 

 to shewe all thinge, that ys seene through yt, to 

 seeme bigger and perfecter, then that yow may 

 see yt withoute the Glasse, and the thynner vnto 

 the sydes and edges. And the thicker that yt 

 ys in the middle, the bigger or larger any thinge 

 sheweth vnto the eye, and yf that the glasse bee 

 very cleare, the more perfecter, &c. And now 

 allso in lyke manner for to make a glasse for 

 perspective, for to beholde, and see any thinge, 

 that ys of greate distance from yow, which ys 

 very necessary : for to vie we an army of men, 

 or any castle, or forte, or such other lyke causes. 

 Then they must prepare very cleare, and white 

 Glasse that may bee rounde, and beare a foote 

 in diameter ; as fyne and white Vennys Glasse. 

 And the larger, the better : and allso yt must bee 

 of a good thicknes, and then yt must bee grounde 

 vppon a toole fitt for the purpose. Beynge sett 

 fyrst vppon a syman block, and firste, grynde 

 on the one syde, and then on ye other syde, 

 vntill that the sydes bee very thynn, and the 

 middle thicke. And for that yf the glasse bee 

 very thicke, then yt will hynder the sighte. 

 Therefore yt must bee grounde vntill that the 

 myddle thereof bee not above a quarter of an 

 ynche in thickness : and the sydes or edges very 

 thynne, and so polysshed or cleared. And so 



