C 5°9 1 
Semen virile, he declares, that a Million of the 
Animalcula Teen therein would not equal a large 
Grain of Sand ; and yet he gives a full Defcription 
of their Form 5 for he fays, their Bodies are roundifh, 
fomewhat flat before, but ending {harp behind, with 
Tails exceedingly tranfparent, Five or Six times 
longer, and about Five times flenderer, than their 
Bodies; fo that their Figure cannot better be repre- 
fented, than by a fmall Earth-nut with a long Root 
or Tail. 
Now the Focus of the greateft Magnifier of his 
being of an Inch, as near as can well be mea- 
fured, it is capable of magnifying the Diameter of 
an Objedt (to an Eye that fees fmall Objedts beft at 
Eight Inches) no more than 160, and the Superficies 
25600 times : So that Objedts, One Million whereof 
fcarce equal a Grain of Sand, viewed through fuch 
a Lens, (as only the Superficies can be feen) could 
appear no larger than Two Grains and half of Sand 
would be to the naked Eye ; and I fubmit it to be 
confidered, whether that is not too fmall a Size for 
any Man to deferibe fo particularly, and delineate 
the Form and Parts of. 
But Mr. Leeuwenhoek goes yet abundantly farther : 
For, to mention only one Xnftance, of which there 
are feveral in his Writings; he tells this Society 
in his Letter of July 25. 1684. that he could difeern 
Veflels in the human Eye, fo amazingly minute, that, 
defiring to know their Smalnels, he meafured them 
by the Diameter of a Grain of .Sand, (the Procefs of 
which Menfuration is there fet down) and found by 
arithmetical Calculation, that a large Grain of Sand 
mud 
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