LETTER 21. 5 OCTOBER 1677 iV (e: 
and thereby enabled us to read today a detailed record of some 
of the most remarkable and original researches ever executed. 
The further communication referred to above is 
Leeuwenhoek’s 21st Letter—according to my reckoning— 
and the passages in question are as follows’: 
In my letter of 23 March, 1677, I demonstrated that 
one drop of water (which is as big as a green pea) is 
equal in volume to 92%” millet-seeds: and to bring it 
home to some friends of mine who could not grasp this, 
I took 6 millet-seeds and stuck them alongside one 
another with a little pitch. Then, with a pair of callipers, 
I took the width of the axes of the said millet *-seeds, and 
found the distance between the points was equal to the 
axis of a big currant; and I remarked that the cube of 6 
is 216. Now, said I, let us put an uncertain for a certain 
quantity; and let us say, that as the currant sinks in 
water, and the millet-seeds sink likewise in water, they 
are therefore of like gravity: this being so, then 216 
millet-seeds should weigh as heavy as this currant. I 
then placed the currant in a small but exceeding nice 
pair of scales, and found that 212 millet-seeds were of 
equal weight with the currant. 
I said also* that when I should again have a great 
number of living creatures in water, I would send you 
testimonials thereof, for the satisfaction of yourself and 
the other Philosophers: these I now send you herewith, 
from eight several Gentlemen, some of whom say that 
nn 
"From Letter 21. 5 October 1677. To Oldenburg. MS.Roy.Soe. 
An English abstract was published by R. Hooke in his Lectures and 
Collections (1678), Part II; Letter I, pp. 81-83. (Also reprinted in Hooke’s 
Lectiones Cutlerianae, 1679.) Apparently this letter, though sent to 
Oldenburg, came into Hooke’s hands when he succeeded him—after his 
death—as Secretary of the Society.—This letter is called “ [26] Brief 18B”’ 
by Vandevelde (1922, p.356), who, as he was unaware of the existence of 
the original MS., could assign no date to it. My translation is made from 
the manuscript itself. 
? This is a mistake. It should be 91 (91°125). See p. 169 supra. 
® In the MS. the word geerst (= millet) is here miswritten “ geest’’. 
* 7.e., in his letter of 23 March 1677. See p. 171 supra. 
