LEEUWENHOEK’S WRITINGS 389 
including fragments and copies of letters addressed to others, 
they amount approximately to 200. At present I cannot 
enumerate them more exactly. (Their number is grossly 
overstated by most previous authors, who apparently count 
originals and translations and printed proofsheets as “ original 
manuscripts.) As these manuscripts form the basis of the 
present work, I may add the following notes upon them: 
The Roy. Soc. MSS. (mostly Dutch) were very incompletely 
and imperfectly printed in the form of extracts or abstracts, 
in English or Latin, in contemporary numbers of the Philo- 
sophical Transactions and Hooke’s Philosophical Collections 
(which replaced the Transactions between Vol. XII, 1678-9, 
and Vol. XIII, 1682-3). These periodicals contain approxi- 
mately 120 printed “ extracts’ from Leeuwenhoek’s letters, 
though the “extracts” do not represent exactly the same 
number of original letters. The printed versions will all be 
found in Phil. Trans. Vol. VIII (1673) to Vol. XXXII (1723) 
inclusive [none in Vols. XVI and XXX], and are indexed— 
more or less accurately—by Maty (1787). Similar “ extracts” 
from 2 letters were included in Hooke’s Lectures and Collections 
(1678)—reprinted in his Lectiones Cutlerianae (1679)—and of 
3 others in his posthumous Philosophical Haperiments and 
Observations edited by Derham (1726). 
Many of these manuscripts were published in full, however, 
in Leeuwenhoek’s printed Dutch and Latin collective works, 
and 14 of the previously wholly unpublished early Dutch 
letters have just appeared in Opuscula Selecta Neerlandicorum, 
Vol. IX (1931): while two of the letters sent to the Royal 
Society, together with a fragment of Letter 116, have passed 
somewhat mysteriously into the Sloane MSS. now preserved 
in the British Museum. (I say ‘mysteriously’ because the 
honourable Sir Hans Sloane, M.D., had no obvious right to 
incorporate any of Leeuwenhoek’s original letters, addressed 
to him as Secretary of the Society, in his own private 
collection.) 
Other surviving manuscripts of Leeuwenhoek are known to 
me only through more or less recently printed versions or 
descriptions. I have not yet been able to study all the 
originals, but note their existence here for the help of others: 
The Leeuwenhoek Manuscripts in the Huygens Collection at 
Leyden (University Library). Eight in number, and now 
printed in Guvres Complétes of Chr. Huygens (see especially 
