De la Croze called Leeuwenhoek a "curious Observer of Nature"

May 23, 1693

In 1693, Jean de la Croze (also Crose) published one volume of Memoirs for the Ingenious, a journal set up on the model of Philosophical Transactions. The issue of May 1693 included an English translation of Leeuwenhoek's Letter 65 on the circulation of blood in frogs. Dobell (p. 61) called the translation "neither complete nor accurate, though written in a language which gives no cause for complaint".

Letter 65 (AB 110) was not published in Philosophical Transactions. It was not published in Latin by Leeuwenhoek until 1695. Thus, de la Croze may have translated the Dutch version of the letter published by Leeuwenhoek in 1687 in Natuurs Verborgentheden Ontdekt: zijnde een Tweede Vervolg der Brieven, geschreven aan de Koninglijke Societeit tot Londen. It seems more likely that he translated the Dutch in the pamplet that Leeuwenhoek published that had only Letter 65 and that he gave to visitors to his home who saw his showcase experiment of blood circulating through a frog's tail. The pamphlet, titled Den Waaragtigen Omloop des Bloeds (On the True Circulation of the Blood), was a reprint of the letter as it appeared in Tweede Vervolg der Brieven.

De la Croze added the comment below about Leeuwenhoek.

De la Croze does not say when he visited Leeuwenhoek. His comment has three problems:

  • In May 1693, Leeuwenhoek was 60 years old, not 50. Perhaps he was 50 when De la Croze visited him.
  • Leeuwenhoek was not a surgeon by training or trade. It is easy to understand how De la Croze could have thought that after he saw Leeuwenhoek's skill in dissection.
  • The microscope made of a short tube with a lens on each end, that is, the traditional compound microscope, was one that as far as we know Leeuwenhoek never made or spoke of using. Its qualities were inferior to this own magnifying glasses. This mistake suggests that De la Croze never actually visited Leeuwenhoek.

Memoirs for the Ingenious, p. 152

Mr. Leeuwenhoek being so deservedly famous in the learned World, the Ingenious will undoubtedly be glad to have an account of him. He is about 50 years of age, but has already imployed 15 or 20 years in Observations as curious as these, which I have here related. His Parents designed him for a Chyrurgeon, which Profession he has exercised sometime with Honor. And as he rightly conceived, that Anatomy was the foundation of that useful Art, and that Microscopes were highly serviceable to acquire the knowledge of it, he applied himself not only to perfect those that were already in use, but even to invent new ones, in which he has succeeded to admiration, having discovered amongst other things more kinds of invisible Animals, than the World before him knew there were visible ones: and withal made an anatomical description of many of them.

The perfection to which he has brought his Microscopes, has afforded him great light. For they are not big and cumbersom tools, as the ordinary ones; but light and portable, consisting only of a glass or two at the end of a small and short tube, so that he may manage them, and apply them to the object, as easily as his own Eyes. And what is fill more wonderful is, That tho his Glasses magnify the Objects far beyond any I have seen, yet they do not darken it. To which if it be added, that he is an able Surgeon, and has made it his chief business during many years to dissect and view little Animals, Plants, Seeds, Eggs, Saps and the like, his surprising discoveries will become more credible.

I know some are apt to imagine, that this curious Observer of Nature imposes at least upon himself, in several things which appear to them undiscernible. But as to the matter of fact he relates, I dare answer for his sincerity, having myself tried his Microscopes, viewed several things through them, and found them conformable to his relations.

Besides, he is very free to let Objects be viewed through his Glasses, and to communicate his Observations to Gentlemen of Learning and Credit, especially Travellers: but he has made so many of them at all seasons and times of the year, that the Thousandth part cannot be examined by those that repair to him on that account. There is a Volume of his Observations printed in Latin, some of which are inserted in the Philosophical Transactions, and I have by me some other very curious, which I shall publish in due time.