Robert Hooke wrote Letter L-117 to Leeuwenhoek that his observations were well received by the Royal Society

March 20, 1682

In this letter, Hooke transmits to L. a copy of Philosophical Collections, nos. 4 and 5, containing two letters by L. that Hooke has translated. He praises L.’s discoveries about muscles, which agree with his own, and encourages L. to further his investigations.

The date is New Style, which was ten days ahead of the Old Style date of 10 March used by Hooke in London.

A copy is in London, Royal Society, Early Letters, H3.69. Another copy is in London, Royal Society, Letter Book Original supplement 4 GH.30.98, pp. 397-398, titled, “Dr’s Answer to Leeuwenhoek’s Letter of Mar: with remarks on the Structure of Muscles.” That copy is the one transcribed below.

Leeuwenhoek summarizes the contents of this letter in the beginning of Letter L-119 of 4 April 1682 and repeats a paragraph at the end of that letter, suggesting that he either had it translated by someone or that he could read some English himself. For another such instance, see Letter L-123 of 26 February 1683 from Francis Aston to Leeuwenhoek.

Hooke’s previous letter to Leeuwenhoek is the lost Letter L-115 of December 1681. Leeuwenhoek replied with Letter L-116 of 3 March 1682 about, among other things, muscles in mammals and fishes and his discovery of the nucleus of a cell. Hooke’s next letter is Letter L-118 of 26 March 1682.


Signed autograph letter. The manuscript is to be found in London, MS. Sloane 1039, f. 172, British Museum; 1 quarto page.

Letter Book Original supplement 4 GH

March 10:1681/2 (O.S.) in London

Worthy Sir,

Yours of this instant March came safe to my hands as did also that which you sent in November last: but I much wonder to understand that you had not received my answer to it, when you wrote this last. I shall therefore now again acquaint you that I translated both this and your former, and communicated them to the Society at their meeting, who were extreamly well pleased with your excellent Discoveries, and ordered me to return you their hearty thanks, as also that I should take care, as soon as might be, to get them published in the Collections: which I have accordingly done, and have herewith also sent them for your Perusal. I have as near as I could followed the Sense of your Expressions, that not verbatim.

Your Discoveries both in the former and this are very considerable: but I am not a little pleased to find by this last that you have discover’d the same thing in the muscles of the flesh, which I long since did in those of Fish; especially in those of Lobsters, Crabs, Shrimps, of which I gave you some advertisements about four years since, at which time I also shewed them to the Royal Society at their meeting namely that the muscles of these Creatures consisted of an innumerable company of exceeding small Filaments or Strings almost a hundred times smaller than a Hair of my Head; each of which Filaments was of the Shape of a String of Pearl or Beads of Glass: so that a small String of such a Muscle as big as a Hair seem’d like a Necklace of small Seed Pearl, which is usually made up of a great number of small Strings of such small Seed Pearl.

Signr Borelli in a posthumous Book of his of the Motion of Muscles seems to confirm also this fabrick of a Muscle: and now your Observations have clearly proved it, so that I conceive there can remain no further Doubt. But you have yet carry’d us farther, and discover’d to use the Texture even of these Filaments; and thereby shown us also the Reason of their Contraction more clearly. Go on, Sir, with these your most excellent Inquisitions and that you may be happy and successful in making further and further Discoveries into the Arcana and Mysteries of the hitherto invisible & unknown parts of the World, is the hearty wish of the Royal Society, so also of,

Worthy Sir,

    Your most affectionate &
    very humble Servant
    Robert Hooke S.R. Secr.