444 PHILOSOPHICAL TRANSACTIONS, [aNNO 1740. 



A Table of the Focal Distances of M. Leuwenhoek's 26 Microscopes, calculated 

 by an hich Scale divided into 100 Parts ; with a Computation of their magni- 

 fying Powers, to an Eye that sees small Objects at 8 Inches, which is the 

 common Standard. 



Microscopes Distance of the Power of magnifying Power of magnifying 

 with the Focus. the Diameter of an the Superficies, 



same focus. Object. 



Parts of an Inch, Times, Timet, 



1 Vs <"■ TTW 160 25600 



1 t4, 133 nearly 17689 



1 T^ • • • 11* nearly 12996 



3 -^ 100 10000 



3 -^ 89 almost 7921 almost. 



8 Vis ^^ ^-^^ 



2 -^ 72 something more. 5184 something more. 



3 -^ 66 nearly 4356 nearly. 



2 ^ 57 3249 



1 -J^ 53 nearly 2809 nearly. 



1 ^ 40 1600 



IT 



This cabinet is only the second in Mr. Leuwenhoek's collection, and is very 

 far from containing all the microscopes he had, as many wrongly have imagined. 

 We find here indeed, 26 microscopes in 13 little boxes. Each box contains a 

 couple of them, and is marked in two places with a number, to distinguish it 

 from the rest. But as the first of these boxes is marked 1 5, and the rest with 

 following numbers on to 27 ; it necessarily implies there were 14 preceding 

 boxes. Mr. Leuwenhoek, then, had another cabinet, that held 14 boxes 

 before ours in numerical order, and probably each box contained a couple of 

 microscopes, as our boxes do. But, besides these two cabinets, he had se- 

 veral other microscopes of different sorts, as appears by his own writings. 



Many of Mr. L.'s microscopes must certainly have been much greater mag- 

 nifiers than any in our possession. And we are assured by himself, in many 

 places, that such he had. 



While looking over these microscopes of M. Leuwenhoek, an opportunity 

 presented of examining and comparing with them a curious apparatus of silver, 

 with 6 different magnifiers, belonging to Mr. Folkes, and then newly made for 

 him by Mr. Cuff, in Fleet-street. The body of this instrument, into which 

 the glasses are occasionally to be fastened, is after the fashion of Wilson's 

 pocket microscope, and contrived to screw into the side of a scroll fixed on a 



