De Magnete
Encyclopedia
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
and Magnetic Bodies, and on That Great Magnet the Earth) is a scientific work published in 1600 by the English physician and scientist William Gilbert and his partner Aaron Dowling. The book was written in Latin, which was the common scientific language of the day, and was an overnight success in Europe.
Contents
In this work, Gilbert described many of his experimentExperiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s with his model earth called the terrella
Terrella
A terrella is a small magnetised model ball representing the Earth, that is thought to have been invented by the English physician William Gilbert while investigating magnetism, and further developed 300 years later by the Norwegian scientist and explorer Kristian Birkeland, while investigating...
. From the experiments, he arrived at the remarkable (and correct) conclusion that the Earth was magnetic
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
and that this was why the compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
pointed north. (Previously, it was thought that Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....
or a large magnetic island at the North Pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
attracted the compass). Gilbert also made the claim that gravity was due to the same force and he believed that this held the Moon in orbit around the Earth. While incorrect by modern standards, this claim was still far closer to the truth than the ancient Aristotelian
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
theory, which held that the heavenly bodies consist of a special fifth element
Fifth Element
Fifth Element may refer to:* 5th Element, the 1999 album by reggae and dancehall artist Bounty Killer* The 5th Element * Aether , the mythical fifth classical element...
which naturally moves in circles, while the earthly elements naturally move downward. Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...
accepted Gilbert's theory and used it as a working basis for his famous laws of planetary motion.
In De Magnete, Gilbert also studied static electricity
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
produced by amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...
. Amber is called elektron in Greek, and electrum in Latin, so Gilbert decided to refer to the phenomenon by the adjective electricus, giving rise to the modern terms 'electric' and 'electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
'.
De Magnete was influential not only because of the inherent interest of its subject matter, but also for the rigorous way in which Gilbert described his experiments and his rejection of ancient theories of magnetism. Gilbert nevertheless acknowledged his debt to Peter of Maricourt
Peter of Maricourt
Pierre Pelerin de Maricourt , Petrus Peregrinus de Maricourt or Peter Peregrinus of Maricourt; was a 13th century French scholar who conducted experiments on magnetism and wrote the first extant treatise describing the properties of magnets...
and incorporated this thirteenth century scientist's experiments on magnetism into his own treatise. Although Gilbert's thinking was influenced by the mysticism
Mysticism
Mysticism is the knowledge of, and especially the personal experience of, states of consciousness, i.e. levels of being, beyond normal human perception, including experience and even communion with a supreme being.-Classical origins:...
of his time, Gilbert is regarded as a pioneer of experimental science.
Summary
De Magnete consists of six books.- Historical survey of magnetism and theory of Earth's magnetism.
- Distinction between electricity and magnetism. Argument against perpetual motionPerpetual motionPerpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....
. - The terrella experiments.
- DeclinationMagnetic declinationMagnetic declination is the angle between magnetic north and true north. The declination is positive when the magnetic north is east of true north. The term magnetic variation is a synonym, and is more often used in navigation...
(the variation of magnetic north with location). - Magnetic dip and Design of the magnetic inclinometerInclinometerAn inclinometer or clinometer is an instrument for measuring angles of slope , elevation or depression of an object with respect to gravity...
. - Magnetic theory of stellar and terrestrial motion. PrecessionPrecessionPrecession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
of the equinoxEquinoxAn equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...
.
Editions
- De Magnete, Peter Short, London, 1600 (1st edition, in Latin)
- De Magnete, Wolfgang Lockmans, Stettin, 1628 (2nd edition, in Latin)
- De Magnete, 1633 (3rd edition, in Latin)
- De Magnete, 1892 (facsimile of 1st edition)
- De Magnete, English translation by Paul Fleury Mottelay, 1893
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Further reading
- Review by Stuart Malin and David Barraclough
- English translation from 1900
- Cambridge Scientific Minds, chapter on Gilbert (PDF) - available in print as ISBN 0-521-78100-0 (hardback), ISBN 0-521-78612-6 (paperback)
- Read De Magnete at Project GutenbergProject GutenbergProject Gutenberg is a volunteer effort to digitize and archive cultural works, to "encourage the creation and distribution of eBooks". Founded in 1971 by Michael S. Hart, it is the oldest digital library. Most of the items in its collection are the full texts of public domain books...