Geomagnetism

A. Kircher. Magnes, siue, De Arte Magnetica Opus Tripartitum, 1643

We have been using compasses to help us find our way since the eleventh century. Still, it wasn’t until 1600 that William Gilbert, in his De Magnete, suggested that the earth itself was somehow magnetic. And only in the last century have scientists generally agreed on the cause: the churning of the earth’s molten outer core is effectively working like a giant dynamo.

A. Kircher. Magnes, siue, De Arte Magnetica Opus Tripartitum, 1643

Before settling on this dynamo theory, much work was done and innumerable geomagnetic observations were made. The Vail Collection is rich in such formative research. Just as important as landmarks like Gilbert’s De Magnete and Athanasius Kircher’s Magnes, are the more commonplace accounts of everyday observations. Efforts like those documented in Samuel Hunter Christie’s Discussion of the magnetical Observations Made by Captain Back and Humphrey Lloyd’s Account of the Magnetical Observatory of Dublin contributed to the foundation upon which our current understanding of the earth’s magnetic field now stands.

W. Gilbert. De Magnete, 1600

These observations contributed to a better understanding of how magnetic declination – the difference between true north and magnetic north – changed from time to time and from place to place. This better understanding led to better navigational charts and better navigational instruments, and thus to safer and more reliable navigation.

While many of these geomagnetic works principally contain tables of data, several are adorned with breathtaking maps of the earth’s magnetic field. Others offer more confounding displays of the earth’s magnetic properties. Consider, for example, this throng of people being violently tossed into the air, or what appears to be a pig flying in the background of this engraved title page.

Return to Magnetism

Magnetologia curiosa, 1690