This work contains all that was known in his day on the subject of electricity and magnetism. While William Gilbert's De magnete (1600), the first thoroughly modern treatment of magnetism, influenced Kircher considerably, Kircher adapts Gilbert's theories of magnetism and Kepler's work in astronomy, but does not hesitate to refute either.

Kircher's Magnes is filled with curiosities, both profound and frivolous. The work does not deal solely with what modern physicists call magnetism. Kircher discusses, for example, the magnetism of the earth and heavenly bodies; the tides; the attraction and repulsion in animals and plants; and the magnetic attraction of music and love. He also explains the practical applications of magnetism in medicine, hydraulics, and even in the construction of scientific instruments and toys. In the epilogue Kircher moves from the practical to the metaphysical (and Aristotelian) when he discusses the nature and position of God: the central magnet of the universe.

This work contains the first use of the term "electro-magnetism", (page 640). This work, like others of Kircher's printed works, became very popular. The Magnes had a powerful influence upon Otto von Guericke, while Jungius, Leibniz and others quoted from Kircher's works.

The work is divided into three parts: the first on the magnet itself; the second on its application (encompassing magnetic statics, magnetic geometry, magnetic astronomy and magnetic natural magic); and the third on such topics as the magnetism of the earth and other heavenly bodies, the use of the thermometer, natural and artificial weather, magnetism of medicines, poisons and antidotes, the attractive force of the imagination, and the magnetism of music and of love. Part III contains a large section featuring the role of magnetism in medicine, including a chapter on Tarantism, the Dancing Mania of the middle ages caused by the bite of the tarantula, and centered on the Italian city of Taranto (in Apulia). This section includes a fine engraved plate of anatomical illustrations of the tarantula. The disease is described and musical examples are provided, including lyrics, musical instruments, and dance steps used in effecting a cure.

Brigham Young catalogue 4; Brunet, III, p. 667; Caillet, Manuel bibliographique des sciences psychiques ou occultes, II, 362.5779; Clendening, Athanasius Kircher, 1602-1680: an exhibition 5.4; De Backer, Bibliotheque des ecrivains.., I, 422-23.5; DSB, VII, pp. 374-378; Graesse, IV, 21; Haskell Norman Library 1215; Krivatsy, NLM, 6398; Merrill 4; Mottelay, Bibliographical history of electricity & magnetism, p. 120; Poggendorf, I, 1259; Ronalds, Catalogue of books .. relating to electricity, magnetism .. (1880), p. 267; Sommervogel, IV, 10048-49.6; Thorndike, VII, p. 269;