Where did he do his scientific work?

Until Leeuwenhoek moved in, the upper floor front of the Gulden Hoofd was all one room, two windows looking onto the Hippolytusbuurt, a fireplace on one wall, and a built-in bed in the far corner.

At some point, Leeuwenhoek partitioned off the northern third of it, just enough to include one of the windows. That created a space (#15) that was very narrow and not much longer with a bed built into the end opposite the window (the "X").

Leeuwenhoek always referred to it as his comptoire, with the usual variant spellings. In the Philosophical Transactions translations and in Alle de Brieven / Collected Letters, it is called a study or a closet, sometimes a counter, and in one 1685 letter, an office. In 1678, Hooke called it Leeuwenhoek's "counting-house".

The notes in Alle de Brieven / Collected Letters, vol. 2, pp. 78, 79, indicate in error that this comptoire was on the ground floor. They paraphrase Schotel's Het Oud-hollandsch huisgezin der 17de eeuw:

The ground-floor of a Dutch house in the 17th century had a number of small windows with lead-lights behind a lattice or bars, through which the light fell into the entrance-hall and the ‘closet’. In this entrance-hall the merchant had his shop. His ‘counting-house’ was partitioned off. This closet was also common in gentlemen's residences. It was often the boudoir of the mistress of the house or served as a parlour, not because there were not better and larger rooms, but in order to keep these clean and ready for immediate use.

All of that is true of many houses, but it's not true of Leeuwenhoek's, which was comparatively narrow. On the ground floor, the front room had no partitioned-off area. Leeuwenhoek's "counting-house" was the inner room, what the estate inventory called the binnenkamer. It had a fireplace and a window to keep track of what was going on in the shop.

The word "laboratory" did not come into general usage until the mid-19th century, in parallel with the word "scientist". However, that's the best translation of comptoire in the sense of a physical space dedicated to:

  • making and storing tools and instruments
  • collecting, preparing, and storing specimens
  • performing experiments and making observations
  • the business of science: organizing bench notes and sketches, scientific letters and drawings, manuscripts, proofs, translations, reference books, and correspondence
  • the business of fame: entertaining visitors

In short, a laboratory.

In Letter 18 (AB 26) of October 10, 1676, Leeuwenhoek described his laboratory in some detail. Alle de Brieven / Collected Letters used this translation from Philosophical Transactions, restoring only the passage in brackets from the manuscript:

My Study stands toward the North east, in my Antichamber, and is very close joyned together with Wainscot, having no other opening than one hole of an inch and a half broad, and 8 inches long, [through which the wooden spring of my lathe passes] towards the street furnisht with 4 windows, of which the two lowermost open inwards, and by night are closed with two wooden Shuts.

Leeuwenhoek's Dutch:

Mijn comptoir staet tegen het noort oosten, is op mijn voor camer met greijnen hout seer digt in een gevoegt, afgeschooten ...

Three problems:

  • The phrase op mijn voor camer is the same phrase used in the estate inventory: op de voorkamer. All the rooms on the upper floors were referred to with op and those on the ground floor only with in. For example, the room on the ground floor below the voorkamer was referred to as in de voorhuis.
  • Antichamber in the sense of a small room leading to a main one is also a mis-translation, not surprising because the translators in England had never been to the Gulden Hoofd. The voor means front, as opposed to achter, behind. In relation to the front of the house, the achterkamer was behind the voorkamer, with no implication of relative size.
  • The next phrase, greijnen hout seer digt in een gevoegt, literally translates as "grainy wood very closely joined together". For afgeschooten, past participle of afschieten, to slip off or slide off, Sewel's dictionary includes this phrase: "Afschieten met een middelschot, To separate with a partition".

Thus, an alternate translation:

My laboratory stands toward the northeast, and is partitioned off from my front room with a wooden panel, having no other opening than one hole of 1 1/2 inches broad, and 8 inches long, through which the wooden spring of my lathe passes towards the street furnished with four windows. The two lowermost open inwards, and by night are closed with two wooden shutters.

If the lathe did not fit, either he had not planned for it, or the slit in the wall was a design trade-off to keep the bedroom as large as possible. He also doesn't mention a door.

In any event, the laboratory was a tiny room, about 168 cm in width, with a total floor space under nine square meters. Compared to a medium-sized modern bed, the room was barely the width of its mattress and about two and a half times its length. It was that room that Leeuwenhoek referred to repeatedly in his letters.

-- some examples --