There seems to be general agreement that the first known horseshoe magnet (permanent, not electromagnet) was produced by the instrument maker Johann Dietrich of Basel, probably in 1743. Dietrich also produced magnetic needles for precision measurement of the inclination of Earth's magnetic field. Daniel Bernoulli used both kinds of Dietrich's magnets in his magnetism research.
However, it is not clear whether Dietrich really invented the horseshoe magnet, or rather produced one at the suggestion of Daniel Bernoulli. So far, all I see is disagreement among secondary sources, and I don't really see what primary sources they are using to reach their conclusions.
References I looked at so far
- Coey, Magnetism and Magnetic Materials (2010). The relevant text reads (see here):
An important civilian advance, promoted by the Swiss polymath Daniel Bernoulli, was the invention in 1743 of the horseshoe magnet. This was to become magnetism's most enduring archetype. The horseshoe is an ingenious solution to the problem of making a reasonably compact magnet which will not destroy itself in its own demagnetizing field.
As to which source Coey used, in Further reading section of that chapter, the most likely reference seems to be Kloss, Geschichte des Magnetismus (1994) (here). Unfortunately, I have no access to it.
- Forbes and Dijksterhuis, A History of Science and Technology, Vol. 2 (1963). The relevant section reads (see here),
The first kind of magnets used were chiefly bar magnets. At Daniel Bernoulli's suggestion, the Basle instrument-maker Johann Dietrich bent the bar so as to bring the poles close together, thus creating the first horseshoe magnet.
Looking at the bibliography for the relevant chapter (23), the most likely source is Bibliographical History of Electricity and Magnetism by Mottelay. Unfortunately, if I search in that work or look in its index, I find no hits for 'horseshoe' or 'Dietrich'. However, it could also be that the information comes from one of the references I have no access to, such as
Lincoln, E. S. edit. A Chronological History of Electrical Development (New York, 1946).
- Verhandlungen der Naturforschenden Gesellschaft in Basel, Volumes 24-25 (available for free here). The relevant section, whose translation by Google translate I don't completely understand, is this:
In der Festrede zur Feier des 50jährigen Bestehens der Basler Naturforschenden Gesellschaft (vom 4. Mai 1867, Verh. IV, Anhang ) sprach er über die Arbeiten der Societas physica helvetica , der Vorgängerin der Gesellschaft , nicht über die Geschichte dieser selbst, denn , da die Gründer und Erbauer derselben zugegen waren, „ ich habe die Überzeugung, dass es den betreffenden, unter uns hochver ehrten Männern erwünschter ist, das Rühmliche getan zu haben , als das Getane rühmen zu hören ." Der Nachweis, dass die beste Form der Inklinationsnadel der Hufeisenmagnet sei, wie 1743 Dan. Bernoulli in einer Preisschrift bewies, diese aber vom Goldschmied und Instrumentenmacher Joh. Dietrich in Basel zuerst konstruiert worden ist , wie Burckhardt nachweist, dürfte daraus am meisten interessieren.
Here, for what it's worth, is a translation by Google translate:
In the speech to celebrate the 50th anniversary of the Basler Naturforschenden Gesellschaft (May 4, 1867, Verh. IV , Appendix ) he spoke about the work of the Societas physica helvetica , the predecessor of the society , not about the history of this itself, because , there the founders and builders of the same were present, " I am convinced that it is more desirable for the men in question, who are highly respected among us, to have done what is creditable than to hear praise for what has been done." The proof that the best form of the inclination needle the horseshoe magnet is, as Dan Bernoulli proved in a prize paper in 1743, but this was first constructed by the goldsmith and instrument maker Joh. Dietrich in Basel, as Burckhardt proves, should be of most interest.
- Radelet-de Grave, "Studies of Magnetism in the Correspondence of Daniel Bernoulli," in Two Cultures: Essays in Honour of David Speiser, K. Williams, ed. (Birkhäuser, Basel, 2006). Here are the relevant sections:
In the meantime, Daniel Bernoulli is using horseshoe-shaped magnets, invented24 and produced by Dietrich, in order to determine his law giving the magnitude of the force of such a magnet. In several letters he reports an empiric law, which was later published in a rather peculiar text meant to promote the trade of Dietrich’s magnets: it is rather like a commercial advertisement.25
24It is difficult to date the apparition of the horseshoe magnets, which, moreover, were discovered independently in England later on. The publication meant to promote their trade is of 1755. But they are mentioned in the letters earlier than that: Daniel Bernoulli to Johann Jacob Huber (7 June 1754) and to Pierre Bouguer (11 November1754). In the latter D. Bernoulli says that he has been disgusted by this kind of research but he does not give reason why.
The "Text R," to which I don't have access, is the following:
Remarques sur les Aimans artificiels de Basle, Nouvelle Bibliothèque germanique janv. fev. mars 1755
What primary sources are available when trying to understand whether it was Dietrich or Bernoulli who came up with the idea for the horseshoe magnet?
Given these sources, who is most likely to have come up with the idea for the horseshoe magnet: Dietrich or Bernoulli?
Thanks to Tom Heinzl, I was able to access "Text R," here. I will now reproduce the relevant section, which starts on p. 225:
C'est Mr. Dietrich, Bourgeois de cette Ville & habile Artiste, qui fait ces Aimans artificiels. Sa curiosité naturelle le porta d'abord à construire quelques-uns de ces Aimans, en suivant les préceptes connus, & fa capacité le conduisit bientôt à les perfectionner. Il a remarqué que la figure la plus convenable pour donner beaucoup de force à ces Aimans est celle d'un fer à cheval: voici la mesure des parties d'un de mes Aimans, qui pése 9 1⁄2 onces, & qui porte 16 livres: …
Here is the output of Google translate (except for Bourgeois, meaning citizen; the boldfaced emphasis is mine):
It is Mr. Dietrich, a Citizen of this city and a skillful Artist, who makes these artificial magnets; his natural curiosity first led him to construct some of these magnets, following the known precepts, and his ability soon led him to perfect them. He has noticed that the figure most suitable for giving much force to these magnets is that of a horseshoe. Here is the measurement of the parts of one of my magnets which weighs 9 1/2 ounces, and which bears 16. pounds: …
So this source, at least, says that it was Dietrich himself who came up with the horseshoe design. It is still possible that there are other sources that contradict this. (It is this text that Radelet-de Grave describes as a "rather peculiar text meant to promote the trade of Dietrich’s magnets: it is rather like a commercial advertisement.")
The additional two letters mentioned by Radelet-de Grave are available at swisscollections.ch.
The letter to Johann Jacob Huber is available here. Since I don't speak French, I transcribed it using Transkribus, and then used a combination of ChatGPT and Google translate to correct as best as I could the inevitable (i) errors in transcription and (ii) typos in the original, and then produce an English translation. As best as I can, here is the original text and its translation:
Si l'aimant artificiel en forme de fer à cheval et les petites barres appartiennent à la Chambre de Physique, car il me semble les avoir payées, je prie Mr Huber de les remettre à ma servante. Je serai chez moi cet après-midi jusqu'à 3 heures.
If the artificial magnet in the shape of a horseshoe and the small bars belong to the Physics Chamber, as I seem to have paid for them, I ask Mr. Huber to give them to my servant. I will be at home this afternoon until 3 o'clock.
Bernoulli's letter to Pierre Bouguer can be found here. Using the same procedure as for the previous letter, here is my best guess for the relevant part of it and its translation:
Mon observation que la force des aimants artificiels semblables en figure et en surfaces suit la raison de la surface de ces aimants s'est trouvé confirmée par tous les essais que j'en ai faits. Je pourrais bien faire avec le fer les expériences que vous me proposez, si j'en reprenais le goût; mais j'en ai été tellement dégoûté que je me suis défait de tous les aimants artificiels que j'avais pour ne plus les avoir sous mes yeux. J'en ai remis un petit à M. Falckner pour l'autoriser d'autant plus à vous voir.
My observation that the force of artificial magnets similar in shape and surface is proportional to the surface area of these magnets has been confirmed by all the experiments I have conducted. I could perform the experiments you propose using iron if I regained an interest in them; however, I was so disgusted that I got rid of all the artificial magnets I had so that I no longer see them in front of my eyes. I gave a small one to Mr. Falckner to encourage him to visit you more often.
The following reference also seems to be useful, and it was cited in the past (see here):
Ferdinand Rosenberger, Die Geschichte Der Physik in Grundzügen (The history of physics in outline), vol. 2 (F. Vieweg und sohn, Braunschweig, Germany, 1884), p. 297, available here. The relevant section (the only one where either Dietrich or horseshoe magnets are mentioned) is this:
Die Inclinationsboussole selbst suchten Daniel Bernoulli und Euler zu verbessern, indem sie die Bedingungen untersuchten , unter welchen die verschiedenen Inclinationsnadeln übereinstimmende Resultate ergeben mussten. Bernoulli erhielt für die betreffende Arbeit 1743 den Preis der Pariser Akademie , Euler das Accessit. Vielleicht auch auf Veranlassung Daniel Bernoulli's führte um diese Zeit der Baseler Mechaniker Johann Dietrich († 1758) die Ilufeisenmagnete und ihre Armirung ein; wenigstens entdeckte Bernoulli mit solchen Dietrich'schen Magneten das Gesetz, dass die Tragkraft der Hufeisenmagnete proportional ist ihren Oberflächen oder den dritten Wurzeln aus den Quadraten ihrer Gewichte.
Translation via Google Translate, plus Boussole = compass (see here) and Accessit assumed to be Akzessit = second place prize (see here):
The inclination compass itself sought to be improved by Daniel Bernoulli and Euler by investigating the conditions under which the various inclination needles must give consistent results. In 1743, Bernoulli received the prize of the Paris Academy for the work in question, and Euler received the second place prize. Perhaps also at the instigation of Daniel Bernoulli, the Basel mechanic Johann Dietrich († 1758) introduced iron magnets and their armouring around this time; at least Bernoulli discovered the law with such Dietrich magnets that the lifting capacity of the horseshoe magnets is proportional to their surface areas or the third root of the square of their weights.