Period 2 - 1679-1686

Encouraged by his election as a fellow of the Royal Society in London, Leeuwenhoek continued to write letters through the end of 1680. Then a full year passed, November 1680 to November 1681, without a letter. The following year, he wrote only three more. What happened to slow his output?

Perhaps it has something to do with what was happening at the Royal Society after Henry Oldenburg's death. Note the two farthest right columns on the table below. There were three gaps in his publishing history with the Royal Society. The first gap occurred during Period 2. Nehemiah Grew replaced Oldenburg as one of the Society's two secretaries and reluctantly agreed to finish editing volume 12 of Philosophical Transactions, which Oldenburg had begun. I wasn't until 1683 that the Royal Society asked him to resume publication.

Leeuwenhoek responded to this drought and ongoing uncertainty by beginning to publish his letters himself.

The table below summarizes these eight years of Leeuwenhoek's scientific career, from early 1679 through the end of 1686. Robert Plot was the editor for volumes 13, 14, and 15 (Nos 144 to 178) with the help of William Musgrave for volume 15 (Nos 167 to 178). Edmond Halley took over for volume 16.

Letters in Period 2

• AdB #: the letter numbering in Alle de Brieven / Collected Letters.
• # ltrs AdB: the number of letters written by Leeuwenhoek in Alle de Brieven / Collected Letters.
• # ltrs sci: the number of letters with scientific observations.
• AvL #: Leeuwenhoek/Cole's letter numbering.
• # ltrs w/ figs: the number of letters with figures.
• # figs: the total number of figures in all the letters written during that period.
• # ltrs RS: the number of letters sent to the Royal Society.
• # ltrs RS sci: the number of letters with scientific observations that Leeuwenhoek sent to the Royal Society.
• PT vol and no: Philosophical Transactions volume and numbers.
• # arts PT: the number of articles by Leeuwenhoek published in Philosophical Transactions.
• # ltrs Dutch: the number of letters that Leeuwenhoek published himself in Dutch.

* - The difference between the 36 letters with publishable scientific observations and the 25 of them that Leeuwenhoek published are the three to Constantijn Huygens and his son Christiaan, three to Lambert van Velthuizen, three to Robert Hooke, and two to Anthonie Heinsius that Leeuwenhoek excerpted two years later in Letter 60 of November 28, 1687 (AB 105):

1679-04-27    44    Constantijn Huygens
1679-05-15    46    Christiaan Huygens
1679-05-20    47    Constantijn Huygens   1 figure
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    excerpted in Letter 60 of 1687-11-28 (AB 105)
1685-09-21    87    Anthonie Heinsius    excerpted in Letter 60 of 1687-11-28 (AB 105)

The figure in the letter to Constantijn Huygens is Leeuwenhoek's sketch of a cube with hatched sides to illustrate his calculation of numbers of little animals.

** - Another 7 letters written during Period 2 were published in Philosophical Transactions in Period 3 along with the second part of Letter 39 of September 17, 1683, the first part of which was published in Period 2, volume 14, 1684.

From 1678 through the end of 1686, Leeuwenhoek wrote 55 letters, 37 of them to the Royal Society, including a thank-you addressed to the membership as a whole for having elected him a member. Almost half of these letters were addressed to Robert Hooke. Six, over a fifteen-month period in 1678 and 1679, were addressed to Nehemiah Grew (left), secretary of the Society and editor of Philosophical Transactions. Three in the summer of 1680 were addressed to Thomas Gale after he replaced Grew as secretary.

Four went to Lambert Van Velthuysen, a medical doctor from Utrecht and also one of Spinoza's critics and correspondents. Two letters were addressed to Constantijn Huygens. One was addressed to his son Christiaan Huygens.

Only two, the March and May 1678 letters, were published by Grew that same year in volume 12 of Philosophical Transactions.

Three other letters written during this period were eventually published in Philosophical Transactions:

• the letter of January 12, 1680 (AB 54), addressed to Hooke, about wood vessels, was published by editor Robert Plot in volume 13, 1683.

• the letters of April 5, 1680 (AB 57), addressed to Hooke and the letter of May 13, 1680 (AB 58), addressed to the other secretary, Thomas Gale, about rat semen, mussels, and oysters, were published by editor Richard Waller thirteen years later in volume 17, 1693.

Of the remaining 28, Hooke published six, one of the two in Microscopium and five in Philosophical Collections. The other letter in Microscopium, Letter 21 of October 5, 1677 (AB 33 from Period 1), announced Leeuwenhoek's observations of spermatozoa and the correct description of their function.

That left 22 letters. One, as discussed below, was published by Leeuwenhoek himself in Dutch and Latin. One was lost. One was published in a collection of Hooke's papers the year after Leeuwenhoek died. The other 20 remained unpublished until the 20th century.

Learn more about this period of Leeuwenhoek's career year by year on the menus below and top right.