Period 1 - 1673-1679

After the Rampjaar (Disaster Year) of 1672, the lives of many people in Delft changed direction. In the previous four years, Leeuwenhoek had:

  • visited England, using a lens to examine chalk
  • discovered Hooke's Micrographia
  • developed world-class lens grinding skills, and made his first devices to hold them, according to Hooke's instructions
  • "observed the sting of a bee", just as Hooke had
  • become certified as a surveyor
  • re-married
  • become acquainted with medical doctors like Regnier de Graaf

In Delft, the Rampjaar was most critical in the summer. In late June, the Stadhuis, where Leeuwenhoek worked as kamerbewaarder, was occupied for a week by protesters from Schiedam. In September, half of the Veertigraad was replaced by regents loyal to the House of Orange. Later in September, Leeuwenhoek's only surviving child, Maria, made a will describing herself as "sickly". He celebrated his 40th birthday on October 24, 1672.

Then, with the support of Regnier de Graaf, Leeuwenhoek began writing down his observations and sending them to Henry Oldenburg at the Royal Society.


The table below summarizes the first six years of Leeuwenhoek's scientific career, through the first two months of 1679. Oldenburg edited Philosophical Transactions until his death in 1677. Nehemiah Grew was the editor in 1678 for the final five numbers, 138-142, of volume 12.

Letters in Period 1

  AdB # # ltrs
AdB
# ltrs
sci
AvL # # ltrs
w/ figs
#
figs
# ltrs
RS
# ltrs
RS sci
PT
vol
PT
nos
# arts
PT
# ltrs
Dutch
1673 1-3 3  2 1-2 2 13 3 2 8 92-100 ** 2  
1674 4-14 11  8 3-8 3 7 8 6 9 101-111 5  
1675 15-19 5  5 9-13 3 9 5 5 10 112-120 1  
1676 20-29 10  7 14-18 4 15 9 6 10
11
121-122
123-132
2  
1677 30-36 7  4 19-22 1 1 6 4 12 133-137 3  
1678 37-41 5  5 23-26 3 20 4 4  12 138-142 *** 2  
1679 42 1  1 27 0 0 1 1  none      
    42 * 32  27 16 65 36 28     17  0
  • 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 32 letters with scientific observations and the 27 in Leeuwenhoek's numbering are these five letters, numbered by Cole (1937):

1674-04-05      4      2a    Constantijn Huygens
1674-04-24      7      3b    Constantijn Huygens
1676-01-22    20    13a    Henry Oldenburg
1676-11-07    28    18b    Constantijn Huygens
1678-12-26    41    26a    Constantijn Huygens, with 3 figures

In Philosophical Transactions, 15 letters were published in 17 different articles:

** Letter 1 of 1673-04-28 divided into two articles in vol. 8 no. 94 and no. 97
*** Letter 25 of 1678-05-31 divided into two articles in vol. 12 no. 140 and no. 142


According to Alle de Brieven / Collected Letters, Leeuwenhoek wrote 42 letters in the first six years. The bulk of them, 27, were addressed to Henry Oldenburg. Five went to Constantijn Huygens, and one to his son, Christiaan Huygens. One was addressed to Robert Boyle about a subject of his specialty. Three, after the death of Oldenburg in 1677, were addressed to William Brounker, founding president of the Royal Society. After Nehemiah Grew replaced Oldenburg, he got four letters. One was addressed to Robert Hooke.

Of those 42 letters, four were lost and are known only through references to them in other letters. The rest, 38, were eventually published, 14 for the first time only in 1930. Only 17 of these early letters were published during Leeuwenhoek's lifetime:

  • 15 were published in partial English translations in 17 articles in Philosophical Transactions, volumes 8 - 12. See the list of titles under Sources below.
  • 2 were published by Robert Hooke in Microscopium in 1678.

The other 7, mostly to Constantijn Huygens, were first translated into English and published in the late 19th and early 20th centuries, and are now in Alle de Brieven / Collected Letters, vols 1 and 2.


What Leeuwenhoek published himself

Twenty years later, for the Vijfde (Fifth, 1696) and Sevende (Seventh, 1702) volumes of his letters in Dutch, Leeuwenhoek reached back and published three of his letters from this early period:

  • Letter 19 of March 23, 1677 to Henry Oldenburg (AB 31), that Oldenburg excerpted in Philosophical Transactions No. 134 in 1677. Leeuwenhoek included the beginning and the end of the letter in Letter 96 of November 9, 1695.
  • Letter 21 of October 5, 1677 to Henry Oldenburg (AB 33), that Robert Hooke published in the Microscopium part of Lectures and Collections in 1678. Leeuwenhoek quoted part of it also in Letter 96 of November 9, 1695.
  • Letter 22 of November 1, 1677 to Viscount Brouncker (AB 35), about human sperm that had been published in full in Latin translation by newly appointed editor Nehemiah Grew in Philosophical Transactions No. 142 in 1679. Leeuwenhoek included part of it in Letter 113 of December 17, 1698.

Even though he eventually published 165 of his own letters in Dutch and Latin, other than the three excerpts listed above, Leeuwenhoek did not publish any of his letters from these years, 1673 through early 1679. Nor did Samuel Hoole select any for his volumes.

What's odd is Leeuwenhoek's own numbering system. When he published his letters, he began with a letter from April 1679 that he numbered 28. This letter is Cole's number 28, too, and is number 43 in Alle de Brieven / Collected Letters, volume 3. Leeuwenhoek was well aware that at least 27 early letters were not included. Had he not kept copies himself?


What Leeuwenhoek observed

During these years, Leeuwenhoek made the discoveries for which he is best known: protozoa, bacteria, sperm, and red blood cells. Had he died in 1679, we would still be talking about him today.

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