[ 5°4 ] 
Martin Folkes, Efq; * and found it fiich an exad and 
full Defcription of their Structure and Ules, as renders 
any farther Attempt to that Purpofe intirely needlefs. 
1 had likewife the Pleafure to find, that the judicious 
Obfervations of this Gentleman, on the Goodnefs of 
the Giafles, and the admirable Dexterity of Mr. Leeu- 
wenhoek in the Management and Application of the 
Objects fitted to them, had reduced my Task to fo 
narrow a Compafs, that little more is left for me to 
offer than a Calculation of their magnifying Powers, 
fome Refkdions arifing from fuch Calculations, and 
a brief Account of what Improvements in Micro- 
icopes have lately been made among!! us. 
In order to this, the firft thing I went about, was 
to view attentively the Objeds applied to thefe Mi- 
crofcopes by Mr. Leeuwenhoek himfelf, which Mr. 
Folkes has given a Lift of in his Account •> but the 
greateft Part of them were, I found, deftroyed by 
Time, or (truck off by Accident; which indeed is no 
Wonder, as they were only glewed on a Pin’s Point, 
and left quite unguarded. Nine or Ten of them, 
however, are (till remaining ; which, after cleaning 
the Giafles, appeared extremely plain and diftind, and 
proved the great Skill of Mr. Leeuwenhoek , in adapting 
his Objects to fuch Magnifiers as would fhew them 
beft, as well as in the Contrivance of the Apertures 
to his Giafles, which, when the Objed was tranfparent, 
he made exceeding fmall, fince much Light in that 
Cafe would be prejudicial : But, when the Objed 
itfelf was dark, he inlarged the Aperture, to give it 
9U 
* Philofophical Tranfatlions , N 0 }8o. 
