LEEUWENHOEK’S MICROSCOPES 329 
The minute biconvex lens (J, fig. 4) was mounted between 
two thin oblong plates of brass (or other metal). Towards 
one end of each plate, at the same point in the middle line, a 
concavity was ground or punched and a hole pierced in its 
centre. When these apertures had been made to coincide 
exactly, the lens was clamped between the plates, in the 
concavities (as shown in fig. 4), and secured by four equidistant 
rivets forming the corners of a square (see fig. 1) with the lens 
at its centre. In other words, the rivets and the lens—in 
surface view—formed a quincunx, the lens occupying the 
central spot. 
The two oblong metal plates’ with the lens thus mounted 
between them constitute the essential optical part of the 
instrument. Leeuwenhoek probably kept many of his lenses 
so mounted, and fixed interchangeable mechanical parts to 
them as required. These mechanical accessories— for focussing 
the object before the lens-—are shown in the figures and have 
been well described by Mayall in his Cantor Lectures (1886) 
as follows: ‘“‘ The object is held in front of the lens, on the 
point of a short rod, the other end of which screws into a 
small block or stage of brass [whose peculiar shape is shown 
from above in fig. 2], which is rivetted somewhat loosely on 
the smoothed cylindrical end of a long coarse-threaded screw 
[figs. 1, 4] acting through a socket angle-piece | fig. 3] attached 
behind the lower end of the plates by a small thumb-screw 
[s, fig. 4. Only the projecting end of this screw is visible 
in fig. 1. It is furnished with a roughly-fashioned metal 
washer above the angle-piece—shown in section in fig. 4]. 
The long screw serves to adjust the object under the lens in a 
vertical direction, whilst the pivoting of the angle-piece [fig. 3] 
on its thumb-screw [fig. 4, s] gives lateral motion. ‘The 
object-carrier can be turned on its axis, as required, by 
screwing the rod into the stage [by means of a metal knob, 
shown in figs. 1 and 4. When the rod is rotated by moving 
the knob, the object is not only turned on its axis but raised 
or lowered by the screw passing through the block—thus 
forming a sort of “fine adjustment” for the “coarse adjust- 
ment” provided by the long screw]. For focussing, a thumb- 
1 The brass lens-holding plates of the best Haaxman specimen measure 
approximately 41 mm. by 18 mm.; but their sides are not accurately 
parallel, and their corners are roughly rounded. 
