While this was the shortest of the seven periods of Leeuwenhoek's publication history, it was pivotal. The Royal Society was so successful, its members' research so broad and deep, that what was seen as one -- natural philosophy, what we now call science -- was becoming too complex.

The first great division was between the researchers who used lots of mathematics and those who didn't. Astronomy, from Copernicus, Brahe, Kepler, and Galileo to van Leeuwenhoek's contemporaries Edmond Halley, Christiaan Huygens, and Isaac Newton, used mathematics to "see", to make sense of their numerical data, which was basically all they had. Biology and botany "saw" more directly. Human researchers sought patterns with their eyes, not with numbers.

Up through this period, the editors of Philosophical Transactions published articles, reviews, and letters of both types, what we'll call the physical sciences and the biological sciences. The editor after Oldenburg's death, Nehemiah Grew, was mostly a botanist. Robert Plot, who agreed to be editor after Hooke stopped Philosophical Collections, did research of both types. He was joined in his third year and volume by William Musgrave, a physician who wrote about human diseases.

In this three-year period, Leeuwenhoek wrote 19 letters, 11 of them to the Royal Society. He addressed two in 1683 to Christopher Wren, four to Francis Aston, and five to the members of the Royal Society in general.  All were eventually extracted and published in the Philosophical Transactions in 12 different articles.

  • the first two, January 22, 1683 (AB 70), and July 16, 1683 (AB 72), were addressed to Wren. Robert Plot published them in volume 13 of 1683 along with the letter from January 1680 from period 2.
  • the next three -- September 17, 1683 (AB 76), December 28, 1683 (AB 79), and April 14, 1684 (AB 80) -- were addressed to Aston. Plot published the in volume 14 of 1684. A shorter extract from the letter of September 17, 1683, an entirely new translation with the figures reversed and missing one of them, was published in volume 17 by Richard Waller.
  • of the next four, July 25, 1684 (AB 81), was addressed to Aston and January 5 and 23, 1685, and March 30, 1685 were addressed to the members of the Royal Society. William Musgrave published them in volume 15 of 1685.
  • the next two -- July 13, 1685 (AB 85) and October 12, 1685 (AB 88), were published by Richard Waller in volume 17 of 1693. (See Period 5.)

The situation was such at the Royal Society that both secretaries, Aston and Hooke, resigned on December 9, 1685. They were replaced a week later by John Hoskins and Thomas Gale. Seven years were to pass before Leeuwenhoek would have another letter excerpted in Philosophical Transactions.

Interspersed with these letters, Leeuwenhoek addressed eight letters of the period's 19 letters to Anthonie Heinsius. Cole was not aware of their existence when he compiled his list in 1937. Their first publication was in Alles de Brieven / Collected Letters volume 4 in 1952.


January 22, 1683

  Wrote Letter 37 of 1683-01-22 (AB 70) to Christopher Wren
May 20, 1683 Wrote letter of 1683-05-20 (AB 71) to Anthonie Heinsius
July 16, 1683 Wrote Letter 38 of 1683-07-16 (AB 72) to Christopher Wren
July 22, 1683 Wrote letter of 1683-07-22 (AB 73) to Anthonie Heinsius
September 2, 1683 Wrote letter of 1683-09-02 (AB 74) to Anthonie Heinsius
September 16, 1683 Wrote letter of 1683-09-16 (AB 75) to Anthonie Heinsius
September 17, 1683 Wrote Letter 39 of 1683-09-17 (AB 76) to Francis Aston
September 30, 1683 Wrote letter of 1683-09-30 (AB 77) to Anthonie Heinsius
October 14, 1683 Wrote letter of 1683-10-14 (AB 78) to Anthonie Heinsius
December 28, 1683 Wrote Letter 40 of 1683-12-28 (AB 79) to Francis Aston
January 1, 1684 Published Onsigbare Geschapene Waarheden (Invisible Creation Truths), Letters 32, 39
January 1, 1684 Published Humor Cristallinus (Crystalline Humor), Letter 41
January 1, 1684 Published Eyerstok (Ovary), Letters 37, 39
January 1, 1684 Published Onsigbare Geschapene Waarheden (Invisible Creation Truths), Letters 32, 33, 39
January 1, 1684 Published Eyerstok (Ovary), Letter 37
January 1, 1684 Published Onsigbare Geschapene Waarheden (Invisible Creation Truths), Letters 32, 33
January 1, 1684 Published Schobbens in de Mond (Scales in the Mouth), Letter 40
April 2, 1684 cousin Margrieta Maertens Leeuwenhoek married Michiel Reijniers van Hasseld
April 14, 1684 Wrote Letter 41 of 1684-04-14 (AB 80) to Francis Aston
May 26, 1684 William Molyneux demonstrated blood flow in a newt
July 25, 1684 Wrote Letter 42 of 1684-07-25 (AB 81) to Members of the Royal Society

December 13, 1684

  sister Catharina Philips Leeuwenhoek received legacy from great uncle Johan Sebastiaans van den Berch
December 20, 1684 cousin Geertruijt Huijchs Leeuwenhoek buried