WILLIAM GILBERT, AND TERRESTRIAL
MAGNETISM IN THE TIME OF
QUEEN ELIZABETH: A DISCOURSE
BY SILVANUS P. THOMPSON, F.R.S.

WILLIAM GILBERT AND TERRESTRIAL MAGNETISM IN THE TIME OF QUEEN ELIZABETH.

William Gilbert, the father of electrical science, was born in Colchester in 1540. Educated at St. John's College, Cambridge, where he took his degree as Doctor of Medicine in 1569, he settled, after four years of foreign travel, in London in 1573, and was admitted to the Royal College of Physicians, of which he became Censor, Treasurer, and, in 1599, President. He was in February, 1601, appointed personal Physician to the Queen, whom he attended in her last illness. He came of a well-known East Anglian family, and held extensive landed estates in Essex and Suffolk. He survived the Queen only eight months, dying November 30th, 1603.

Gilbert's monumental work, the De Magnete, published in 1600, marks an era in magnetic science. For some four hundred years the employment of the magnetic needle in navigation had been known both in Northern and Southern Europe. While it is possible that the primitive use of the loadstone may be ascribed to the Baltic, it is certain that the employment of a pivotted needle, and the addition of a rose of the winds as a compass card both originated in the Mediterranean. The pivotted needle is described in the Epistle of Peter Peregrinus, written in 1269; while the earliest known compass-card marked with the initials of the names of the winds is that ascribed to Jachobus Giraldis, of 1426, in the Biblioteca Marciana in Venice. The manner of use in Elizabethan times of the loadstone and of the compass may be gathered from Olaus Magnus (Historia de Gentibus Septentrionalibus, 1555), from Pedro de Medina (Arte de Nauegar, 1545), Martinus Cortes (Breve compendio de la sphera, 1556), Blundevile (Exercises, 1594), Norman (Newe Attractive, 1581), Borough (A discours of the Variation of the Cumpas, 1581), Pedro Nuñez (Instrumenta Artis Navigandi, 1592), Barlow (The Navigators Supply, 1597), Nautonier (Mécometrie de l'Eyman, 1602), and Stevin (Die Havenvinding, 1599).

At the time when steering by the compass was introduced into navigation, the compass pointed in Middle Europe so nearly truly to the north that with the rough instrumental appliances at hand its deviation from the true north was seldom noticed, or if noticed ascribed to some error in the setting of the needle. Later the compass-makers began to set their needles slightly askew beneath the card, according to the variation in the place of origin. Norman (1581) states that those used in the Levant, made in Sicily, Genoa, or Venice, had the needles straight, while those used in Denmark and Flanders had them set at three-quarters of a point, or a whole point, to the eastward; while those made in Spain, Portugal, France, and England, had the needles set half a point to the east. Those for Russia were set at "three seconds of a point." Gilbert denounced these devices as tending to obscure the true facts. Gradually it became recognized, probably