The Letters

Antony van Leeuwenhoek wrote only letters, hundreds of them. He wrote them in Dutch, the only language that he knew. These letters, his complete scientific output, are our only direct access to his work and ideas.

  • A little over half of the letters with publishable scientific observations (166 of 285) were illusrtrated with figures, over twelve hundred in total. Leeuwenhoek drew only a few of them himself.
  • He dated all but a few of the letters.
  • He addressed all but a few of them to a specific person or group, most commonly to members of the Royal Society
  • He numbered the 165 letters that he published himself and usually, though not always, put the number at the beginning of each letter in the self-published volumes.

Almost all the letters included several different topics. Leeuwenhoek provided a summary list of those topics at the beginning of most of the letters, a table of contents without the page numbers, but he did not give each letter a title. Thus, the best way to distinguish them is by the date and the number -- for example, Letter 1 of April 28, 1673 -- whether his own numbers, the expanded list made by Cole (1937), or the comprehensive list of 364 in Alle de Brieven / Collected Letters.

The letters in Alle de Brieven / Collected Letters were not the only letters Leeuwenhoek wrote, of course. His correspondence with his Leiden printers and booksellers alone must have been extensive. He would have corresponded with his visitors before and after their visits. He would have corresponded with his sister in Rotterdam and his friend Maria Duyst, who lived in Den Haag and Utrecht. None of this correspondence has survived.

Overview of Leeuwenhoek's Letters

 Period AdB # # ltrs
# ltrs
AvL # # ltrs
w/ figs
# ltrs
# ltrs
RS sci
# arts
Ph Tr
# ltrs
1-42 42 32 1-27 * 16 of 28 65 36 28 17 0
2 Works I
43-96 54 36 28-52 24 of 25 219 38 28 10 25
3 Works II
97-137 41 33 53-83 28 of 31 315 36 31 8 31
4 Works III
138-236 99 73 84-146 35 of 63 194 29 24 19 63
237-294 58 49 [147]
29 of 44 244 51 49 44 0
6 Works IV
295-346 52 46 I-XLVI 22 of 46 144 13 13 2 46
347-364 18 16 [XLVII]
9 of 15 46 18 16 15 0
51 years   364  285  251  163 of 252  1227 223 189 117 165

Key to the tables in this section:


The seven periods of Leeuwenhoek's career. Period 2, 3, 4, and 6 cover the years during which he published Works I, II, III and IV. The other three periods come before, after, and between those four.

AdB #

The letter numbering in Alle de Brieven / Collected Letters.

# ltrs AdB

The 364 letters written by Leeuwenhoek in Alle de Brieven / Collected Letters. It includes but does not number several letters to Leeuwenhoek.

# ltrs sci

The 285 letters with scientific observations. The other 79 were cover letters, query letters, thank-you letters (for example, for his election to the Royal Society), dedications, and copies of letters. See chart below.

AvL #

Leeuwenhoek's letter numbering 1-146 and I-XLVI supplemented by Cole's additions in square brackets during Periods 5 and 7. Cole preserved the spirit of Leeuwenhoek's numbering system by numbering the 59 letters written during Periods 5 and 7 that had publishable scientific observations. He also included letters between Leeuwenhoek's by adding an a, b, or c to the previous number, for example, 26a or [172a].

The difference between these 251 letters numbered by Leeuwenhoek and all the letters with scientific observations are the 34 letters that he wrote but did not publish himself. Only one of them had figures, a letter in 1679 noted with an asterisk on the table above.

# ltrs w/ figs

The 163 letters with figures. In his self-published volumes, he included 109 of these letters. * Every letter with figures is included in Leeuwenhoek's numbering system except one to Constantijn Huygens in Period 1. See chart below.

# figs

The 1227 figures, an average of 7.5 in the 163 letters with figures. About three-quarters of them illustrated his self-published volumes.

# ltrs RS

The 223 letters sent to the Royal Society's members in general or to specific officers in London. The total includes query letters and thank-you letters. It does not include letters to people on the continent like Christiaan Huygens or Gottfried Liebniz who were members of the Royal Society but to whom Leeuwenhoek sent letters that he did not expect to be published in Philosophical Transactions.

# ltrs RS sci

The 189 letters with scientific observations that Leeuwenhoek sent to the Royal Society or its officers with the intention that they be published, about two-thirds of all the letters with scientific observations.

# arts Ph Tr

The 117 articles in Philosophical Transactions that excerpted xxx letters by Leeuwenhoek. The articles were not always published in the same year or even the same period in which the letters were written.

# ltrs Dutch

The 165 letters that Leeuwenhoek published himself in Dutch, year of first editions only. He also published all of these letters in Latin translation, though not usually in the same year. The Dutch and Latin volumes went through multiple editions, for which Leeuwenhoek made hardly any changes in the text though he did change the front and back matter.

The bar chart below displays in blue the number of letters with scientific observations (# ltrs sci on table above) that Leeuwenhoek wrote in each year as well as, in orange, the equal or smaller number of those letters that contained figures (# ltrs w/ figs on table above).