Monthly Archives: November 2009

William Gilbert: On the Lodestone

I recently read William Gilbert’s renaissance masterpiece “On the Lodestone”, and found his work to be extremely intriguing.  Gilbert lived at the dawn of the scientific era, from 1544-1603, predating Francis Bacon – originator of the modern scientific method – by about 20 years.  He is considered by some to be the father of electromagnetism, and indeed is the first to use the term “electricity” in describing what we now know as static electricity (the primary source of static electricity in Gilbert’s experience was amber; the Greek word for amber is elektron). 

Gilbert is a staunch defender of the experimental basis for Truth – at least most of the time.  He attacks earlier writings concerning magnetism as simple repetitions of prior writings which generally are based in nonsensical assertions, which could be easily discounted if anyone bothered to acquire a magnet and observe its behavior.  In the sixteenth century, the primary source of magnetism was the naturally occuring mineral magnetite (ferrous-ferric oxide), or lodestone.  It should be understood that the best (purest) lodestones are barely capable of lifting iron objects of their own weight – very unlike modern “magnets” which generally can lift objects much heavier than themselves, particularly in the case of rare earth magnets which can lift several thousand times their own weight.

Gilbert attacks many myths about the magnet – that coating a lodestone with garlic oil removes the magnetism; that a diamond placed near a lodestone similarly destroys its power; that electrical attraction and magnetism are the same force.  In each case he makes strong derogatory statements about earlier authors who never even saw, let alone tested, a lodestone.  Gilbert proceeds to build a set of facts and observations of his own, each supported by experiment.  Many of his observations I had never considered before (as a trained physicist).  For example:

  • To determine the north and south poles of a magnet, allow the magnet to rotate freely in Earth’s magnetic field.  Mark the end that points to geologic north as the south pole, and the end that points south the north pole.  Which of course makes perfect sense, since opposing poles attract.
  • Apply a magnet’s pole to the center an iron bar, thereby magnetizing the bar.  If you use the north pole of the magnet, this will create north poles at both ends of the bar.   If the bar is curved into a C shape, there will be a repelling force between the cusps of the C.
  • Cut a magnet in half, holding one piece firmly. The cut ends will immediately repel each other, causing the free magnet to rotate rapidly to bring the opposite end to face the cut end.  This implies a continual stress present in  the material near the poles of any magnet.

Gilbert uses spherical lodestones, which he calls “terrellas” for “little Earths” for many of his demonstrations.  Using a device of his invention, the “versorium” – basically a compass needle mounted on a very free-turning point – he maps out the magnetic field lines of the terrella, and demonstrates their equivalence to the directions in which a compass points as it travels over the Earth.  Furthermore, he demonstrates the equivalence of the “dip” of the versorium at high “latitudes” on the terrella with the corresponding subtle dip of an accurate three-dimensional compass observed by navigators as they sail in higher latitudes.  The dip is caused again by the attraction of the pole, which is both north and “under” the compass increasingly as we reach higher latitudes.

There is a wealth of additional experimental and empirical information Gilbert conveys in this work, about not only magnetism, but static electricity as well – I am only remembering the highlights as I write this, some 3 months after finishing it.  And so Gilbert would appear to be a solid hero of scientific reasoning, living at the very end of the middle ages, and opening the door to the coming scientific revolution.  And, as far as the material above, this is certainly the case.

The first inkling we have that Gilbert may not be consistent in his scientific thinking is when he begins describing the relationship between the lodestone and the Earth.  He accurately shows that iron ore and lodestone are related – the one is attracted to the other; the iron can take on weak magnetic properties after exposure to lodestone.  But then he makes a large leap – which just happens to be true – in asserting that the Earth is mostly made from magnetic materials (iron and lodestone), and that what we experience on the surface – bodies of water, various soils, mountains and canyons – are but aberrations of the Earth that exist only on the relatively small surface in comparison to the bulk of the planet.  He, of course, has no experimental evidence for this claim (our experimental evidence came hundreds of years later in mapping how earthquake tremors penetrate the planet).

However, his entire thesis for the work is to explain magnetism, not merely describe its effects and laws.  And this is where he turns shockingly away from reason.  The magnet is aligning itself to the Soul of the Earth – so he asserts without demonstration.  Further, the Earth is a living Being, and this Soul is not a literary euphemism – it is asserted to be real.   After building up a large assortment of truly impressive scientifically-verified facts, and teasing the reader along the way, indicating that his studies have lead to a determination of the true Nature of the lodestone, he quite suddenly moves from demonstration to dogmatic assertion.  In addition to the Earth as a living entity, he goes on to assert that all celestial bodies are alive, each with its own Soul, and that each will exert a force on the material from which it is made, just as the Earth exerts a force on lodestone and iron.  He winds up this strange path through the irrational with an appeal to astrology – that these same forces affect the development of humans born under the various stars and constellations.  If it weren’t so tragic, it would almost be comical.

Gilbert is a fascinating example of an intellectual genius caught between two radically different philosophical worlds, with one foot planted in each.

Report This Post