the line along which the needle set itself. Then laying the needle on other parts of the stone, he obtained more lines in the same way. When the entire surface of the stone had been covered with such lines, their general disposition became evident; they formed circles, which girdled the stone in exactly the same way as meridians of longitude girdle the earth ; and there were two points at opposite ends of the stone through which all the circles passed, just as all the meridians pass through the Arctic and Antarctic poles of the earth.[1] Struck by the analogy, Peregrinus proposed to call these two points the poles of the magnet: and he observed that the way in which magnets set themselves and attract each other depends solely on the position of their poles, as if these were the seat of the magnetic power. Such was the origin of those theories of poles and polarization which in later ages have played so great a part in Natural Philosophy.
The observations of Peregrinus were greatly extended not long before the time of Descartes by William Gilbert or Gilbert[2] (b. 1540, d. 1603). Gilbert was born at Colchester: after studying at Cambridge, he took up medical practice in London, and had the honour of being appointed physician to Queen Elizabeth. In 1600 he published a work[3] on Magnetism and Electricity, with which the modern history of both subjects begins.
Of Gilbert's electrical researches we shall speak later: in magnetism ho made the capital discovery of the reason why magnets set in definite orientations with respect to the earth; which is, that the earth is itself a great magnet, having one of its poles in high northern and the other in high southern latitudes. Thus the property of the compass was seen to be included in the general principle, that the north-seeking pole of
- ↑ "Proeul dubio omnes lincae hujusznodi in duo puncta concurrent sicut omnes orbes meridiani in duo concurrunt polos mundi oppositos."
- ↑ The form in the Colchester records is Gilberd.
- ↑ Culielmi Gilberti De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure: London, 1600. An English translation by P. F. Mottelay was published in 1893.
