The attraction of natural magnets on iron was known since antiquity. The effects produced by terrestrial magnetism on magnetized needles were applied to the compass, a major aid to navigation, already known in the thirteenth century. In the late sixteenth century came the discovery of magnetic inclination, that is, the vertical component of the Earth's magnetic field. William Gilbert, in his De Magnete, opened a new phase in the study of magnetism and electrical phenomena. This heightened the demand for large permanent magnets, with which interesting and surprising experiments could be performed. Later, the systems for magnetizing iron bars artificially were improved. Investigations and measurements of terrestrial magnetism—essential to navigation—became ever more methodical and sophisticated. The nineteenth century saw the invention of electromagnets, significantly more efficient than natural magnets. Various aspects of the magnetic characteristics of matter were discovered. Magnetic and electrical phenomena were brought together in the broader framework of electromagnetic theories.