Magnetic variations at sea, 1628.

ENGLAND - JUNE 10: Engraving from �De magnete� (On the magnet) by William Gilbert (1540-1603), published in Stettin, Poland, in 1628. Gilbert's experiments in magnetism, and his use of such terms as �electric force�, �electric attraction�, and �magnetic pole�, are the basis of the growth of the field of electricity. He discussed the earth's magnetism by making a model - a spherical piece of loadstone called a terrella (little earth). Originally published in 1600, this book is considered the first great scientific work published in England. Added for this unauthorised second edition, this engraving demonstrates Gilbert's belief that the 'inequalities' of the earth's surface, the oceans and continents, caused magnetic variations. This shows a stylised North Sea complete with a sea monster. (Photo by SSPL/Getty Images)