Thomas Gale wrote Letter L-169 to Leeuwenhoek reviewing his recent "ingenious and curious communications"

March 12, 1686

The newly chosen secretary of the Royal Society, Thomas Gale, wrote a friendly, encouraging letter to Leeuwenhoek, dated 2 March 1686 O.S., reviewing some of his recent observations.

Other than the letter and diploma that Royal Society secretary Gale sent in 1680 to certify Leeuwenhoek’s election as a fellow of the Royal Society, Letter L-101 of 7 March 1680, this 1686 letter is the only known letter to Leeuwenhoek from Gale, who had returned to the office of secretary on 16 December 1685 after a five-year hiatus. It was written in response to Leeuwenhoek’s Letter L-166 of 12 October 1685.

Three months after L. wrote that letter, it was read at the regular weekly meeting of the Royal Society on 13 January 1686 O.S.:

Part of a letter of Mr. Leeuwenhoeck, translated by Mr. Lodwick, was read, concerning embryo-plants, which he affirmed himself to have found perfectly formed in some sorts of seeds, particularly the cotton-seed.

Mr. Lodewick was desired to proceed in translating the remainder of that letter.

Martin Lister, the Society’s vice-president who was chairing the meeting, responded, “Plants are sometimes full of a mealy substance, viz. in the spring: which substance, after the plants are run up, is no longer found in them.”

Francis Lodwick (1619–1694) was an English linguist and cloth merchant of Flemish origin who became a fellow of the Royal Society in 1681. He translated several of Leeuwenhoek’s letters for the Royal Society in the mid-1680s, as well as works of Johannes Swammerdam, Cornelis Bontekoe, and Daniel Mitz.

It took almost two months for Lodwick to translate the letter and get it to another meeting, on 3 March 1686 O.S.:

Part of Mr. Leeuwenhoeck’s letter of Oct. 12, 1685, was read, concerning chyle, sweat, pores of the skin, the crystalline humour of the eye, and the optic nerve. The rest was reserved to another meeting.

At that next weekly meeting, on 10 March 1686 O.S.:

A part of Mr. Leeuwenhoeck’s letter was read, containing his observations upon gall and the scales, and slime of the eel and the bream; which slime, he said, he had discovered to be parts of the body of the fish and to consist of a great number of vessels interwoven together; describing the manner how these vessels came out of the scales, that lie under it. The rest of the letter was referred to another meeting.

At the following weekly meeting on 17 March 1686 O.S., there was not enough time to finish Leeuwenhoek’s letter:

Some part of Mr. Leeuwenhoeck’s letter that had not been read in the Society, was ordered to be read at the next meeting.

By the time the next meeting came, they already had another letter from Leeuwenhoek, and there is no record that they ever finished the letter of 12 October. See Birch, The History of the Royal Society of London, vol. IV, pp. 452, 464, 467, 468.

The present letter was written by Gale just before the second of those readings. Leeuwenhoek’s reply, Letter L-173 of 2 April 1686, begins.

I was exceedingly pleased to read, in your favour of the 2nd/12th March, written by Your Honours’ Secretary Mr. Thomas Gale, the special expression of your appreciation, both in regard to my person and my observations contained in some of my previous letters, and to learn also the reason why my letters remained unanswered so long.

Immediately following that, L. breaks the middle two paragraphs of Gale’s letter into four passages that he translates with accuracy and responds to in detail. Later that year, when L. published this letter in Cinnaber Naturalis (Natural cinnabar), he set these translated passages in italics. It is doubtful that L. knew enough English by 1686 to make the translations himself, but he does not mention having anyone’s help.

After the fourth passage, Leeuwenhoek paraphrased the present letter’s final paragraph but attributes it to Robert Hooke.

Mr. Robert Hooke requests me, in view of the lack of eggs of the silk-worm this springtime, to examine the seed of frogs, and to note the manner in which nature proceeds in the reproduction of these animals; for it may be assumed (says that Gentleman), or reasonably asserted, that the generation of most, if not of all, egg-laying fishes proceeds in the same way.

This reference to Hooke is puzzling because the previous letter that Hooke sent to L. was Letter L-117 of 26 March 1682, in this volume, and in no prior letter to L. does he mention frogs or their reproduction. A possible solution is in the sentence that begins that final paragraph: “They have yet one further request to you.” The copyist could have written “They” where the original letter that L. read could have said “Mr. Hooke has yet one further request to you.”

The copy of the present letter in the Royal Society archives is unsigned, contributing to why it is misattributed to Edmond Halley in MacPike, Correspondence and Papers of Edmond Halley, along with Halley’s statement at the beginning of Letter L-176 of 25 May 1686, “Since my last of the 2d of March.” See Letter L-170 of 12 March 1686.


Transcribed here from the copy of the letter in London, Royal Society, Letter Book Original 11A.16, p. 38. A note in the margin says “Journal No. 8 p. 64”. This letter is not in Alle de Brieven / Collected Letters. The spelling and punctuation have been modernized.

An answer to Mr Leewenhoecks Letter of Octob. 12 sent Mart 2 St. Vet. 1686


Worthy Sr.


Yours of the 12 of Octob[1] to Mr. Aston[2] was by him safely delivered to the Royal Society, who have so great a value for so constant, and so communicative a correspondent to let your letters go unanswered so long; but so it is, that the Society being unexpectedly deprived of the service of Mr Aston by whom the whole charge of the correspondence was undertaken, their affairs were very much retarded thereby, and it is but lately that they have reassumed their meetings upon a new model, which they conceive may be less subject to the like inconveniences[3] so that for this time they beg your excuse, and promise you for the future a more ready returneof their thanks, for your ingenious, and very curious communications.

Your letter contains in it a great many particulars[4], in all which you fail not to add some new discovery or to confirm the old, and especially where you tell them that the cotton seed contains it it a perfect plant capable to shift for itself without any oleaging pabulum, as is ordinary in the seed of most other plants, to maintain its deriving its infancy, if I may so say, however they think it worth the considering whether those plants you examined might not be somewhat too old, that so the substance designed for nutriment might be dried up and extenuated so as to pass for leaves or else whether there might not be contained within the stem which in your figures you design large[5], a substance analogous to the yolk of an egg as it is in the bellies of chickens and undoubtedly in those insects you mention to have found without a pabulum in their shells, but this only by way of inquiry, and to know your opinion thereon: you likewise advance an opinion that the hitherto supposed pores of the skin are rather the most compact parts thereof, and that the cuticula is in those little cavities more firmly than ordinary affixed by some ligatures to the cutis, which though it be strong is not without great show of probability, especially if upon view the sweat be found to flow less freely through those pores than elsewhere.

Another of your discoveries, it is to be feared, will pass for paradoxical in the judgment of most men, to wit, that whereby you find the slime of eels, and other fish not an excrement but a real necessary part of their bodies, and likewise to have scales of its own, this is what the Society wonders at, and would be glad they had glasses capable to show them those miracles, which though upon your credit they dare not disbelieve, yet their satisfaction would be more entire, could they but see them themselves[6]. Lastly your speculations upon mixtures of several chemical liquours with the blood, are in the opinion of the Society highly worth the prosecuting, there being hopes that by this means some light may be drawn towards the discovery of the abstruse and mysterious of some medicines in the body, those effects, though never so surprising are not otherwise known than by their symptoms this therefore they recommend to your further examination with hearty wishes of success, there being scarce anything more beneficial to mankind than would be the advancement of the most imperial art of medicine into a scientifical knowledge.

They have yet one further request to you, that since at this time the eggs of silkworms, and the things that happen to them could not by reason of the foregoing hard winters be observed by you, they desire you this spring to view the spawn of frogs, and to note the method that nature takes in the production of those animals, for it is reasonable to suppose that the generation of most if not all oviparous fishes is after the same manner.


[1] Letter 88 [47] L-166 of 12 October 1686, Collected Letters, vol. 5.

[2] Francis Aston (1644-1715) was first secretary of the Royal Society from 1681-1685. See Letter L-123 of 26 February 1683, n. 1, in this volume, for an overview of his correspondence with L.

[3] For details about Aston’s sudden resignation and the resulting new model of organization for the Royal Society, see the Remarks to Letter L-161 of some time between 9 August and 22 October 1685, in this volume.

[4] Gale responds, in the same order, to some of the observations that L. discussed in that long Letter 88 [47] L-166 of 12 October 1685, ibidem.

[5] See Fig. 8, Letter 88 [47] L-166 of 12 October 1685, ibidem.

[6] Because the Royal Society did not have the ability to replicate all of L.’s observations, they had to accept his claims “upon your credit”. Fifteen years later, Royal Society president John Somers made a similar comment, also using “credit”, in his response to L.’s announcement of the bequest of these 26 microscopes: “Such of them [L.’s observations] as have been tried by any other of their members have been so exactly verified by * experiments, that the Society give an entire credit to your relations of matters of fact.” See Letter L-395 of 15 November 1701, in this volume. After L.’s death, Royal Society vice-president Martin Folkes also made a similar comment. “But we have seen so many, and those of his most surprizing discoveries, so perfectly confirmed, by great numbers of the most curious and judicious observers, that there can surely be no reason to distrust his accuracy in those others, which have not yet been so frequently or carefully examined”. See Letter L-599 of late 1723, idem, vol. 19.