Anthonie Heinsius

friend from the Stadhuis in the 1660's who went on to become Grand Pensionary of the Republic
Birth or Baptism date: 
November 23, 1641
Death or Burial date: 
August 3, 1720

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Heinsius was a lawyer in Delft and member of the Veertigraad whose talents led him to become the city's pensionary (chief administrative officer). He would have regularly interacted with Leeuwenhoek. This early part of Heinsius's life is discussed in detail in Het verstand komt met het ambt, referenced below.

The same year that Leeuwenhoek was appointed city inspector, 1679, Heinsius left Delft when he became pensionary for Delft in the States of Holland. In 1682 stadholder William III of Orange appointed Heinsius special negotiator to France. The mission was a failure but he made a favourable impression on William III.

Leeuwenhoek wrote six letters to Heinsius in 1683, when he was beginning his political career outside Delft. He wrote two more in 1685. In 1688 (Letter 65), Leeuwenhoek used him as a reference when writing to the Royal Society:

Some time ago when I was reporting to a certain Professor of Medicine my discovery relating to the circulation of the blood, this Gentleman told me that, when people were discussing my observations, and referring to them in confirmation of certain Matters, the response frequently was: are we to believe it just because Leeuwenhoek says so; what certainty do we have about it. For which reason that Gentleman warned me, and said that I would do well to produce an attestation of a few prominent persons who might have been eye-witnesses to these my discoveries, in order that I might suffer less contradiction on such related matters.

It is quite true that, from special considerations, I have not mentioned hitherto (in my letters) anybody by name, amongst those who, together with me, have seen with their own eyes some of the most remarkable things with the aid of my microscopes; but I only said in general that I had demonstrated the same to some Gentlemen with sound knowledge and judgment, Lovers of Natural Science.

But since I now hear that more credence will be given to what I say if I proceed to specify those who have partly seen the aforementioned circulation or course of the blood, concerning that about which I have now written and communicated to Your Honours, I will make no difficulty in mentioning, out of many, those names as I believe will merit the greatest confidence, such as Mr. Cornelis Schravesande, M.D., Full Lecturer in Anatomy and Surgery, Councillor and One-Time Magistrate. Mr. Cornelis Vallensis, LL.D., also Councillor and One-Time Magistrate. Mr. Antoni Heinsius, LL.D., Councillor and Pensionary of this City, and formerly Envoy Extraordinary to His Royal Majesty of France, and recently Commissary of this State to the Court of His Royal Majesty of England.

These Gentlemen, to whom I am accustomed to communicate many of my discoveries, I have shown, among other things, the veritable circulation of the blood, as distinctly as if we were looking with our naked eye at the movement of the water (in a running river).

Within a decade, Heinsius had become, somewhat reluctantly given the grisly history of the office, Grand Pensionary of the whole province of Holland. In that job until his death, he played a crucial role guiding the Republic and William III, prince of Orange, by then King of England, through wars with France and Spain. Leeuwenhoek wrote eight more letters to Heinsius at the end of the century.

A decade after that, toward the end of the Nine Year's War against France, Leeuwenhoek again began addressing letters to Heinsius, by then one of the most powerful diplomats in Europe. One letter 1695, his first to Heinsius in seven years, had a final paragraph that was crossed out for publication in the printer's working copy of the letter preserved at the University of Amsterdam. Leeuwenhoek wrote:

I should not have ventured to importune Your Honour with these discoveries of mine if it were not for the fact that Your Honour had assured me previously that he would find time, in spite of his occupations, to peruse my observations. Concluding, I remain, after presentation of my humble services ...

Both men are buried in the Oude Kerk, and Leeuwenhoek undoubtedly attended the funeral of his old friend in 1720.

Unfortunately, only one letter from Heinsius to Leeuwenhoek has survived.