LEEUWENHOEK’S MICROMETRY 333 
apparatus. His magnifying-glasses were evidently so designed 
that they could be used interchangeably for ‘ microscopes ” 
or ‘‘enchelyscopes”’, as occasion required, by adding the 
appropriate mechanical parts. 
I may also note here that Leeuwenhoek was one of the 
first—if not the very first—to study the structure of solid 
opaque bodies by means of sections. Some which he cut 
with his own hand “by means of a sharp shaving razor ” are 
still in existence. They were enclosed in a little packet 
affixed to an early letter,’ and have remained intact to the 
present day. According to his own description, they are 
(1) “Cork”; (2) ‘‘ White of a writing pen” [parings from a 
quill] ; (3) “ Bits of the optic nerve of a cow, cut crosswise ”’ ; 
(4) “ Pith of elder.” He added the following suggestions for 
looking at these objects : 
: I would venture to recommend that, when one 
of these sections has been brought upon the pin of a 
microscope, you then hold the microscope towards the 
open sky, within doors, and out of the sunshine, as though 
you had a telescope and were trying to look at the stars in 
the sky through it. 
LEEUWENHOEK’S MicroMEtRY.—Before the invention of 
micrometers it was extremely difficult to measure very small 
objects under the microscope: their size could, indeed, be 
only estimated, by reference to other objects of known dimen- 
sions. On an earlier page” we have read Leeuwenhoek’s 
own account of the way in which he assessed the probable 
magnitude of various animalcules, but a few further notes are 
necessary. 
Leeuwenhoek took the inch_(of his land and period) as an 
absolute unit for small measurements. A copper rule,’ with 
1 Letter 4. 1 June 1674. To Oldenburg. MS.Roy.Soc. Partly published 
in English in Phil. Trans. (1674), Vol. IX, No. 106, p.121. L. also sent a 
copy of this letter to Const. Huygens, and this copy—now in the Leyden 
library—has recently been printed in its original Dutch by Vandevelde and 
van Seters (1925). 
* See p. 201 seq., supra. 
3 Referred to on p. 189 supra. 
