Letters with observations not in Leeuwenhoek's numbering system

Leeuwenhoek wrote 36 letters that 1) reported his observations and explained his thinking and 2) were not included in his numbering system, supplemented by Cole for the years 1702-1712. Some of them repeated obersvations and thoughts from a numbered letter. Others were very short, contained in a letter written for another purpose. Two of them, to Constantijn Huygens, had figures.

Both of the 1685 letters to Anthonie Heinsius were excerpted in Letter 60 of November 28, 1687 (AB/CL 105).

Date written	AB/CL #	Addressed to
Period 1
1674-04-05	4	Constantijn Huygens
1674-04-24	7	Constantijn Huygens
1676-01-22	20	Henry Oldenburg
1676-11-07	28	Constantijn Huygens
1678-12-26	41	Constantijn Huygens, 3 figs.
Period 2
1679-04-27	44	Constantijn Huygens
1679-05-15	46	Christiaan Huygens
1679-05-20	47	Constantijn Huygens, 1 fig.
1679-06-13	49	Lambert van Velthuysen
1679-07-11	50	Lambert van Velthuysen
1679-10-13	51	Robert Hooke
1679-11-14	52	Lambert van Velthuysen
1679-11-20	53	Robert Hooke
1680-01-16	55	Robert Hooke
1685-08-10	86	Anthonie Heinsius
1685-09-21	87	Anthonie Heinsius
Period 3
1691-09-18	115	Antonio Magliabechi
1693-10-27	127	Pieter Rabus
Period 4
1695-05-21	145	Pieter Rabus
1695-05-23	146	Maarten Etienne van Velden
1695-07-12	148	Maarten Etienne van Velden
1695-07-21	150	Pieter Rabus
1695-09-10	156	Pieter Rabus
1696-06-01	166	Pieter Rabus
1696-07-23	171	Pieter Rabus
1701-02-09	222	Frederik Adriaan van Reede van Renswoude
1701-04-08	223	N.N. Mayors and governors of the City of Delft
1701-06-21	227	Hans Sloane
Period 5
1703-11-03	242	Hans Sloane
1707-05-17	267	John Chamberlayne
1710-11-11	285	Members of the Royal Society
1711-11-23	289	Anthonie Heinsius
1711-12-29	291	Anthonie Heinsius
Period 6
1715-11-18	316	Gottfried Leibniz
1718-11-28	346	Francisco Cornaro
Period 7
1722-07-07	359	James Jurin

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What Leeuwenhoek wrote ...
Wrote Letter L-005 of 1674-04-05 to Constantijn Huygens about globules in milk and blood and the growth of hair; first mention of red blood corpuscles
Wrote Letter L-009 of 1674-04-24 to Constantijn Huygens about his further observations about blood, bones, teeth, and salt
Wrote Letter L-031 of 1676-01-22 to Henry Oldenburg about forwarding his mail and about sending his observations of little animals in water
Wrote Letter L-045 of 1676-11-07 to Constantijn Huygens summarizing the observations of little animals in Letter L-040
Wrote Letter L-077 of 1678-12-26 to Constantijn Huygens about how son Christiaan's observations of little animals correspond to his own
Wrote Letter L-081 of 1679-04-27 to Constantijn Huygens about the number of sperm in the milt of the cod
Wrote Letter L-084 of 1679-05-15 to Christiaan Huygens to explain more about his observations of little animals
Wrote Letter L-085 of 1679-05-20 to Constantijn Huygens about the number and size of the little animals he was observing
Wrote Letter L-088 of 1679-06-13 to Lambert van Velthuysen about the origin of life and the lack of appreciation by physicians and surgeons
Wrote Letter L-090 of 1679-07-11 to Lambert van Velthuysen about about the chalk produced by gouty patients and about bladder stones
Wrote Letter L-092 of 1679-10-13 to Robert Hooke to inquire of Hooke why he had not received any correspondence from the Royal Society for months, also discussed bladder stones
Wrote Letter L-095 of 1679-11-14 to Lambert van Velthuysen about gout, salt, and drinking tea
Wrote Letter L-096 of 1679-11-20 to Robert Hooke, copying his Letter L-095 of 14 November 1679 about gout, salt, and drinking tea
Wrote Letter L-098 of 1680-01-16 to Robert Hooke, enclosing a copy of Letter L-085 of 1679-05-20 to Constantijn Huygens about the number and size of little animals
Wrote Letter L-162 of 1685-08-10 to Anthonie Heinsius about cochineal
Wrote Letter L-164 of 1685-09-21 to Anthonie Heinsius about cochineal
Wrote Letter L-210 of 1691-09-18 to Antonio Magliabechi about
Wrote Letter L-229 of 1693-10-27 to Pieter Rabus about procreation of the flea, the leather-jacket, and the mite
Wrote Letter L-254 of 1695-05-21 to Pieter Rabus about the eggs and blood vessels of the ray
Wrote Letter L-255 of 1695-05-23 to Maarten Etienne van Velden about the impossibility of small flies being generated from the body of a big dead caterpillars, again refuting the theory of spontaneous generation
Wrote Letter L-261 of 1695-07-12 to Maarten Etienne van Velden about the metamorphosis of caterpillars and of parasitic larvae coming out of a dead caterpillar
Wrote Letter L-263 of 1695-07-21 to Pieter Rabus about the report that a large caterpillar emerged from a woman's ear and fumigation with sulphur to remove it; Leeuwenhoek cannot find any mites in his own auditory canal
Wrote Letter L-270 of 1695-09-10 to Pieter Rabus about his attempt to breed maggots with his own ear-wax as food and a movement in his ear due to the vibration of a little hair against the ear-drum
Wrote Letter L-289 of 1696-06-01 to Pieter Rabus about dowsing rods and the hazel branches used to make them, iron, and loadstone
Wrote Letter L-297 of 1696-07-23 to Pieter Rabus honey-dew on lime-trees; moisture from vine tendrils leads to a theory on the production of lacquer in tropical trees; his Delft friend has lost the capacity to handle the dowsing-rod
Wrote Letter L-383 of 1701-02-09 to Frederik Adriaan van Reede about pores in willow wood and advice for the improvement of peat
Wrote Letter L-384 of 1701-04-08 to the mayors of Delft about his calculation of the difference between the coal measures of Delft and Rotterdam and how to calculate the volume of a pyramid
Wrote Letter L-391 of 1701-06-21 to Hans Sloane about the claimed qualtity of other people's magnifying glasses, injuries to the cornea, and the impossibility of observing the smallest particles of matter
Wrote Letter L-412 of 1703-11-03 to Hans Sloane to thank him for sending recent numbers of Philosophical Transactions and the book on Peruvian silver mines, also as a cover letter for Letter L-413
Wrote Letter L-452 of 1707-05-17 to John Chamberlayne to complain that his four most recent letters to the Society had not been answered; about a bezoar stone and the visit of Corner; offered to send a copy of Letter L-436 to Magliabechi

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Letters with observations not in Leeuwenhoek's numbering system

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