Gottfried Leibniz wrote Letter L-312 to Leeuwenhoek about magnets and the magnetic power of the earth

January 1, 1697

No manuscript is known.

In this undated letter, Leibniz replies to Leeuwenhoek’s observations about magnets and offers his speculations about magnets and the magnetic power of the Earth.

A copy in German translation in the hand of Christoph Gottlieb von Murr is to be found in Berlin, Staatsbibliothek Preuß. Kulturbesitz Ms. lat. fol. 311 B Bl. 46-47, 1 quarto page.

The text of this partial letter from Leibniz to Leeuwenhoek is probably a French translation of a now missing draft letter by Leibniz, sent by him as an enclosure with one of his letters to Louis Bourguet (1678-1742), a French polymath living in Neuchâtel, who wrote on archaeology, geology, philosophy, biblical scholarship and mathematics. Bourguet’s correspondence with Leibniz, published in 1768, contains letters exchanged between December 1714 and 2 July 1716. These letters were provided to Louis Dutens (1730-1812), the 18th-century editor of Leibniz’s correspondence, by Claude-Nicolas Le Cat (1700-1768), “Secrétaire perpétuel” of the Académie de Rouen, through the mediation of Nicolas Gobet (c. 1735-c. 1781), a French historian and mineralogist and “Secrétaire du conseil du comte d’Artois”. See: Dutens, Leibnitii Opera Omnia, vol. 2 (Geneva, 1768), p. 324 (note).

Even though Leibniz visited Leeuwenhoek in 1676, the surviving exchange of letters between them occurred in the final two years of Leibniz’s life, 1715 and 1716. In those letters, magnets are never mentioned. It is then possible that this undated letter fragment is part of a lost exchange of letters from 1697 because Philosophical Transactions, vol. 19, no. 227, published in April 1697, has Leeuwenhoek’s Letter 184 [108] L-318 of 5 April 1697 (Collected Letters, vol. 12), in which he discusses some of the topics Leibniz writes about in this fragment. See note 2 below.

Leibniz’s reading of Leeuwenhoek’s Letter 184 [108] L-318 of 5 April 1697 in Philosophical Transactions no. 227 of the same month or the excerpt in Pieter Rabus’s Boekzaal van Europe of May and June 1697 could have caused him to write to Leeuwenhoek later that year. He begins by thanking L. for his “reply”, which suggests a prior letter from Leibniz as well as a reply from Leeuwenhoek.

Becchi’s chapter “Leibniz, Leeuwenhoek and the School for Microscopists” discusses only the five letters to Leibniz that Leeuwenhoek published in Send-Brieven and the five letters from Leibniz that are in Collected Letters, vol. 17 and vol. 18.


Published in L. Dutens, 1768: Gothofredi Guillelmi Leibnitii Opera Omnia, vol. 2, pp. 92-94 (Geneva: Apud Fratres de Tournes) – French text with the title “Sur l’ Aimant” (On the magnet).

I am glad, sir, to learn by the honor of your reply[1], that according to the exact experiments you have made, the attractive virtue of the magnet is not diminished when it finds itself in a situation contrary to that in which he is disposed to set himself naturally[2]. Yet you would oblige me, by giving me more instruction on it. Your experience of the iron filings, which, according to the position of the magnet, has kept this arrangement, although it is turned all with the magnet, is ingenious and worthy of you. But though there is no sensible difference in this arrangement, when there is a change of situation, it does not follow that the attractive action of the magnet cannot be sufficiently combated, in order that some others its effects be substantially diminished. Because it may be that the effect of this small diminution cannot be sufficiently noticed in the filings, which consists of small and short pieces, which have friction against the bottom, and against each other, and which are already connected. It would require a considerable force to oblige them to place themselves differently, and a great diminution of the force of the magnet would be necessary in order to make the connection cease. And a magnet, somewhat less strong in faith, but moreover similar in all to that which has been employed, might have given them the same arrangement. Thus, the duration of this arrangement does not prove the duration of the force. But if the magnet were to draw or move a needle equal and similar to the same distance, or if the position of the magnet were natural or constrained, it would be more certain of the fact. And we may be sure that the difference is not sensible, because there is no means more calculated to render sensible the degree of the attractive force of the magnet than to make it act upon a needle. It seems, sir, that you have already made similar experiences in the past, and that is what I should like to learn[3].

You say, sir, that the current of the magnetic matter of the earth is very feeble. But it may be objected that it may be in a few encounters stronger than the magnet. For example, suppose that a magnetized needle is urged by two opposing forces, one of the vertical, the other of the attraction, the first coming from the magnetism of the earth, which tries to turn one of the extremities of the needle towards the north, the other coming from the magnetism of the magnet, which tries to attract it and turn it towards it. In this case it may happen that the vertical is stronger than the attraction, for the magnet may be placed at such a distance that it would be able to turn the needle if it were not magnetized, had no inclination to turn to the north, but that he is not capable of surmounting the proper inclination of the needle.

However, I am aware of an answer to this objection, which I submit to your judgment: that is, that the magnetic needle is not turned to the north by the magnetic force of the earth, but by that which it has received from the magnet. Thus assumed that these actions come from certain currents of magnetic matter, this needle will have its own current, though less strong, comparable, however, with that of the magnet.

Thus, the means of learning whether the magnetic force of the globe of the earth may have on the spot a sensible effect upon the magnet, is precisely the research which I have proposed to be examined, namely, whether the change in the situation is substantially opposed to the action of the magnet. I say on the spot, for in the long run it seems to me that the experiments that have been made, learn that a certain situation of long duration may weaken, or even destroy, at the end, the verticality of a magnetised needle and give it to an iron which has none. I say of a needle, for perhaps it is otherwise with the magnet, and perhaps it would retain its first verticality, and still more its attractive force, even if it would remain for a long time in a constrained position.

I have taken the liberty of extending myself, to give you an opportunity, sir, to enlighten me on this matter, which you can do better than anyone else[4].


[1] L.’s letter to Leibniz previous to this letter is unclear. In none of his surviving letters to L. does he mention magnets or loadstones, so perhaps Leibniz refers to a lost letter.

[2] Letter 184 [108] L-318 of 5 April 1697, Collected Letters, vol. 12. L. wrote to the Royal Society about the behaviour of magnets in glass tubes and the influence of iron on magnets under various conditions.

[3] No reply from L. to Leibniz on this topic is known.

[4] Leibniz’s next known letter to L. is Letter 316 L-520 of 5 August 1715, Collected Letters, vol. 17.