.A very good, clean copy of the first edition of this ground-breaking work on magnets and electricity, with the earliest illustration of the appearance of new poles in a broken magnet (Taylor, 586). Niccolò Cabeo, S.J. (1586-1650) trained at the Jesuit collegium in Parma, and the universities of Padua and Piacenza, and became professor of philosophy and mathematics at Parma and Genoa. Philosophia magnetica is a study of the Earth s magnetic properties, as well as a discussion and frequent confutation of the first study on the subject: William Gilbert s De magnete (1600). Cabeo disagreed with Gilbert on an important premise, believing instead that the Earth was immobile (hence its movement not the source of magnetic fields). But he also perfected some of Gilbert s original observations and discoveries, e.g., the electroscope, whilst engaging with the ideas of ancient (Aristotle), medieval (Petrus Peregrinus) and contemporary (G.B. della Porta, Leonardo Garzoni) scholars. Philosophia became the first book in which account was taken of electric repulsion, and in which was the suggestion for mapping the magnetic field by the use of iron filings (Jordan-Smith, 35). The first part is an introduction to magnetic attraction which discusses, for instance, the properties of magnets, why their two sides repel one another, the causes of the movements of magnetic field and their reference points, how longitude can be gathered through magnetism, magnetic directions in relation to the poles and the horizon, and magnetic declination (illustrated with two small world maps showing Terra Australis Incognita, based on Ortelius s Theatrum ). The second part, on magnetic direction, analyses the causes of magnetic attraction (between magnets and non-magnetised objects), whether the north pole of a magnet corresponds with the actual geographical north pole, electrical attraction (based on material exchange, as in the most utilised example: amber, also called electrum ). The third part extends some of the previous topics, including the direction of magnetic attraction in relation to geography, with innovative experiments using iron filings and compass needles. It also includes important observations on the function of the electroscope (Gilbert s invention, which he called versorium ). The fourth part elaborates on the third with additional practical experiments with iron filings, and most interestingly discusses the effects on magnetisation when a magnet is broken in two. Cabeo was sceptical of supernatural properties traditionally attributed to magnets, e.g., that married couples can be reconciled with a magnet; that gold may be extracted from the deepest wells; that the magnet acts as a love philtre, makes one eloquent, and persona grata to princes (Thorndike VII, 168). An attractive copy of this most important work. .This is probably a second issue, with the author s dedication to Louis XIII. It includes the dedication letter ( Rex Christianissimae ) on a2 (blank in the first issue), as well as the king s engraved arms and the printed address Ad Lvdovicvm XIII. Galliarvm et Navarrae regem Christianissimvm on the engraved t-p.
