Pre-gilbertian conceptions of terrestrial magnetism

It is now well known that William Gilbert, in his De Magnete of 1600, first suggested that the earth behaves as a great magnet. By their very nature, however, such explicit statements tend, in retrospect, to be emphasised at the expense of less explicit antecedent ideas and experiments, with the result that, in the example under consideration here, the impression has sometimes been given that before Gilbert there was not the slightest suspicion that the earth exerts influence on the magnetic needle. In fact, Gilbert's conclusion represented the culmination of many centuries of thought and experimentation on the subject.

This essay traces the main steps in the evolutionary process from the idea that magnetic ‘virtue’ derived from the heave, through the gradual realisation that magnetism is closely associated with the earth, up to the time of Gilbert's definite statement.