"Gilbert also discovered the screening effect of a sheet of iron; the method of magnetizing iron by hammering it while it lies North and South; the destruction of magnetism by heat; and the existence around the magnet of an "orbe of virtue," [i.e.,] a magnetic field. He perfected the dipping-needle of Norman, and other instruments of observation. He collected data as to the declination and inclination of the compass in different regions. Using loadstones of many different shapes he observed their actions on one another and on compass-needles. In particular he studied the magnetic properties of a globular loadstone or and found that compass-needles were directed toward its poles, and dipped at various angles over its surface, just as compass-needles do at various regions of the earth's surface. ...His book, over which he spent eighteen years, was published in 1600, and for the next hundred years became the standard work on magnetism. Though denounced by the Church, the theory of terrestrial magnetism was by Gilbert thus firmly established on an enduring basis of fact, and remained a permanent acquisition in science. The publication of the book marked an epoch in scientific development. It was praised by Sarpi, by Galileo, by Kepler. Sir Christopher Wren proposed to erect a statue to its author, while Dryden sang of his enduring fame."