De magnete, magneticisque corporibus, et de mango magnete tellure; Physiologia nova, plurimis & argumentis, & experimentis demonstrate.
London: Peter Short, 1600.
First edition of “the first major English scientific treatise based on experimental methods of research. Gilbert was chiefly concerned with magnetism; but as a digression he discusses in his second book the attractive effect of amber (electrum), and thus may be regarded as the founder of electrical science. He coined the terms ‘electricity,’ ‘electric force’ and ‘electric attraction.’ His ‘versorium’, a short needle balanced on a sharp point to enable it to move freely, is the first instrument designed for the study of electrical phenomena, serving both as an electroscope and electrometer. He contended that the earth was one great magnet; he distinguished magnetic mass from weight; and he worked on the application of terrestrial magnetism to navigation. Gilbert’s book influenced Kepler, Bacon, Boyle, Newton and, in particular, Galileo, who used his theories [in the Dialogo] to support his own proof of the correctness of the findings of Copernicus in cosmology” (PMM). “Gilbert provided the only fully developed theory … and the first comprehensive discussion of magnetism since the thirteenth century Letter on the Magnet of Peter Peregrinus” (DSB). Although this book does appear with some regularity on the market, copies such as ours in fine condition and in untouched contemporary bindings are rare.
“During the fifteenth century the widespread interest in navigation had focused much attention on the compass. Since at that time the orientation of the magnetic needle was explained by an alignment of the magnetic poles with the poles of the celestial sphere, the diverse areas of geography, astronomy, and phenomena concerning the lodestone overlapped and were often intermingled. Navigators had noted the variation from the meridian and the dip of the magnetic needle and had suggested ways of accounting for and using these as aids in navigation. The connection between magnetic studies and astronomy was less definite; but so long as the orientation of the compass was associated with the celestial poles, the two studies were interdependent …
“Gilbert divided his De magnete into six books. The first deals with the history of magnetism from the earliest legends about the lodestone to the facts and theories known to Gilbert’s contemporaries … In the last chapter of book I, Gilbert introduced his new basic idea which was to explain all terrestrial magnetic phenomena: his postulate that the earth is a giant lodestone and thus has magnetic properties … The remaining five books of the De magnete are concerned with the five magnetic movements: coition, direction, variation, declination and revolution. Before he began his discussion of coition, however, Gilbert carefully distinguished the attraction due to the amber effect from that caused by the lodestone. This section, chapter 2 of book II, established the study of the amber effect as a discipline separate from that of magnetic phenomena, introduced the vocabulary of electrics, and is the basis for Gilbert’s place in the history of electricity …
“Having distinguished the magnetic and amber effects, Gilbert presented a list of many substances other than amber which, when rubbed, exhibit the same effect. These he called electrics. All other solids were nonelectrics. To determine whether a substance was an electric, Gilbert devised a testing instrument, the versorium. This was a small, metallic needle so balanced that it easily turned about a vertical axis. The rubbed substance was brought near the versorium. If the needle turned, the substance was an electric; if the needle did not turn, the substance was a nonelectric.
“After disposing of the amber effect, Gilbert returned to his study of the magnetic phenomena. In discussing these, Gilbert relied for his explanations on several assumptions: (1) the earth is a giant lodestone and has the magnetic property; (2) the magnetic property is due to the form of the substance; (3) every magnet is surrounded by an invisible orb of virtue which extends in all directions from it; (4) pieces of iron or other magnetic materials within this orb of virtue will be affected by and will affect the magnet within the orb of virtue; and (5) a small, spherical magnet resembles the earth and what can be demonstrated with it is applicable to the earth. This small spherical magnet he called a terrella …
“In discussing coition Gilbert was careful to distinguish magnetic coition from other attractions. For him magnetic coition was a mutual action between the attracting body and the attracted body. At the beginning of the De magnete he explained several terms that were necessary for understanding his work. One of these was “magnetic coition,” which he said he “used rather than attraction because magnetic movements do not result from attraction of one body alone but from the coming together of two bodies harmoniously (not the drawing of one by the other)” (P. Fleury Mottelay, William Gilbert of Colchester ... on the Great Magnet of the Earth, 1893, p. liv) …
“Book III of the De magnete contains Gilbert’s explanation of the orientation taken by a lodestone that is balanced and free to turn, that is, the behavior of the magnetic compass … the orientation of the compass was simply an alignment of the magnetic needle with the north and south poles of the earth. Gilbert gave numerous demonstrations of this with the terrella as well as directions for magnetizing iron.
“By the end of the sixteenth century, navigators were well acquainted with variations from the meridian in the orientation of the compass. Thus, after discussing orientation, Gilbert turned in book IV to the variations in that orientation. Here he again used the comparison of the phenomena that can be demonstrated with the terrella and those that occur on the surface of the globe. Just as a very small magnetic needle will vary its orientation if the terrella on which it is placed is not a perfect sphere, so will the compass needle vary its orientation on the surface of the earth according to the proximity or remoteness of the masses of earth extending beyond the basic spherical core. Also, the purity of these masses (the amount of primary magnetic property retained by them) will affect the orientation of the compass just as stronger lodestones have greater attractive powers than weaker ones.
“The next magnetic movement that Gilbert discussed was declination, the variation from the horizontal. This phenomenon had been described by Robert Norman in his book on magnetism, The New Attractive (1581). Although Norman had also given an effective means of constructing the compass needle so that it would not dip but would remain parallel to the horizontal, he had made no attempt to account for this strange behavior. As with the other magnetic effects of the compass, Gilbert explained declination in terms of the magnetic property of the earth and the experiments with the terrella. The small needle placed on the terrella maintained a horizontal position only when placed on the equator. When moved north or south of this position, the end of the needle closer to one pole of the terrella dipped toward that pole. The amount of dip increased as the needle was moved nearer the pole, until it assumed a perpendicular position when placed on the pole. A compass on the earth, according to Gilbert, behaved in a similar manner.
“In discussing the variations from the meridian and the horizontal, Gilbert suggested practical applications of his theory. Navigators of the period were concerned with determining the longitude and latitude of their positions on the open seas. Since the deviation from the meridian was constant at a given point, Gilbert thought that if the seamen would record these variations at many points, an accurate table of variation for various positions could be compiled and the problem would be solved. He included detailed instructions for the construction of the instruments necessary for this task …
“The final book of the De magnete, book VI, deals with rotation and in this section Gilbert expounded his cosmological theories. Without discussing whether the universe is heliocentric or geocentric, Gilbert accepted and explained the diurnal rotation of the earth. From the time of Peter Peregrinus’ Letter on the magnet, written in the thirteenth century, rotation had been considered one of the magnetic movements. The assumption was that a truly spherical, perfectly balanced lodestone, perfectly aligned with the celestial poles, would rotate on its axis once in twenty-four hours. Since the earth was such a lodestone, it would turn upon its axis in that manner and thus the diurnal motion of the earth was explained. The theory was taken from Peter’s Letter; the application to the earth was Gilbert’s addition … Much of the criticism directed by Bacon and others against Gilbert’s writing was based upon the sixth book of the De magnete, where Gilbert extended to the cosmos his magnetic theory and the results obtained from his experiments.
“Throughout the De magnete, Gilbert discussed and usually dismissed previous theories concerning magnetic phenomena and offered observational data and experiments which would support his own theories. Most of the experiments are so well described that the reader can duplicate them if he wishes, and the examples of natural occurrences which support his theory are well identified. Where new instruments are introduced (for example, the versorium, to be used in identifying electrics), directions for their construction and use are included. The combination, a new theory supported by confirming evidence and demonstrations, is a pre-Baconian example of the new experimental philosophy which became popular in the seventeenth century” (DSB). Dibner Heralds of Science 54; Grolier/Horblit 41; Heilbron, Electricity in the 17th and 18th Centuries, pp. 169-179; Norman 905; PMM 107; STC 11883; Wellcome 2830.
Folio (282 x 182 mm), pp. [xvi], 240, woodcut printer’s device (McKerrow 119) on title, large woodcut arms of Gilbert on title verso, one woodcut folding plate, 88 woodcut illustrations and diagrams in text (4 full-page), ornamental woodcut headpieces and initials. Contemporary calf.