Leeuwenhoek did not publish any letters after 1718 in book form with his own summaries. The summary below comes from Alle de Brieven / Collected Letters.
In this letter, L. observes the muscular fibres of different animals and determines whether iron becomes magnetic over time.
Signed autograph letter. The manuscript is to be found in London, Royal Society, Early Letters L.4.75; 4 quarto pages.
A contemporary English translation of the letter by James Jurin is to be found in London, Royal Society, Early Letters L.4.76; 3 pages. The letter was read during the meetings of the Royal Society on 3 May and 10 May 1722; Royal Society, Journal Book Original, vol. 13, p. 193-95; Letter Book Original, 15.74.
A certain gentleman from another province, who visited me, said to me, that when iron has been standing for a long time high in the air, it has such a power that it is able to lift a needle on high.
