William Gilbert, and Terrestial Magnetism in the Time of Queen Elizabeth / A Discourse

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 after the voyage of Columbus, when the manifest change in the declination of the needle nearly caused mutiny of the sailors, that the direction of the needle differs at different places; and accordingly navigators began to collect data. The record of the voyage of Columbus states that during his second voyage in 1496 he used for steering the observations made on the declination during his first voyage. The secret of Sebastian Cabot, which he declared when dying to be a divine revelation to him, can have been little else than the idea of using in navigation the local declinations of the compass. On the other hand, Pedro de Medina flatly denied the existence of the declination, adding that if the compass did not show the pole, the fault lay in the defective construction of the compass itself. Columbus had found a point 2½° east of Corvo, in the Azores, where there was no variation, and other navigators explored the agonic lines which crossed the Atlantic and the Indian ocean. According to Humboldt, Alonzo de Santa Cruz in 1530 constructed the first general variation chart. But along with this development of practical interest in the subject there grew up a crop of wild legends to account for the irregularities observed. The reason why the compass needle pointed north, and the reason why it did not point truly north, were alike proclaimed to be due to the stars, to the influence of spirits, or to the existence of loadstone mountains of uncertain locality and of fabulous power. The old traditions of the Arabian Nights, dressed in a newer setting, found themselves justified by the insertion in maps of loadstone rocks, the position of which changed at the fancy of the chartographer. Ptolemy had located them in the Manioles; Olaus Magnus declared them to be under the pole; Garzias ab Horto situated them in the region of Calcutta. The map of Johann Ruysch, which adorned the edition of Ptolemy, publisht at Rome in 1508, showed four magnetic islands in the Arctic Circle. Martinus Cortes placed the loadstone mountains in Sarmatia. Mercator in his great chart depicted two great rocks rising from the sea to the north of eastern Siberia, one being drawn on the supposition that at St. Michael the compass points due north, while the other is further north on the supposition that the compass points due north at Corvo. The map of Cornelius Wytfliet, 1597, shows the same phantom islands. Blundevile, writing in 1594 of the now lost map of Peter Plancius, mentions that he sets down the pole of the loadstone somewhat to southward of the islands that lie east of Groynelande.