Magnetism was discovered, it is said, many centuries ago by a shepherd called Magnes, who tended his flocks on the slopes of Mount Ida in the region that was then called Asia Minor.
Magnes, apparently, noticed his iron crook and the iron nails of his sandals were inclined to cling to a large black stone; he had discovered what we now call magnetite, an iron oxide that happens to be naturally magnetic.
But as we know, the Earth itself behaves as if it had a giant magnet deep inside, and certain birds and animals can use the Earth's magnetic field to navigate.
Pigeons are the most notable example, but up to 60 other species with the same gift have been identified. Some large fish, for example, appear to detect the Earth's magnetic field by using electrical sensors in their snouts called, rather quaintly, the Ampullae of Lorenzini.
Other creatures have tiny crystals of magnetite embedded in their brains; these, rather like iron filings near a magnet, orientate themselves in the direction of the magnetic force.
But in the 1970s one Goesta Wollin surprised the scientific world by suggesting the Earth's magnetic field might have an even more pervasive influence.
It is well known the terrestrial magnetic field changes in intensity from year to year. Its ups and downs can be seen in the records kept at geophysical observatories, and Wollin's thesis was that changes in the average global temperature might be related to these variations.
He had examined magnetic records from more than 40 observatories around the world, and the results - coincidence or not - were clear. They showed that in places where the intensity of the magnetic field had fallen, the fall was followed by an increase in the average yearly temperature; where the magnetic records showed an increase in the field intensity, the average annual temperature had dropped.
Wollin had an ingenious explanation for this apparent link. He pointed out that salt water is an efficient conductor of electricity, and that the great ocean currents, flowing around the ocean basins of the world in a vast clockwise swirl within the Earth's magnetic field, might have electric currents induced in them as if each was a giant electric generator or dynamo.
Because of this electrical relationship, variations in Earth's magnetic field might affect the rate at which these giant ocean currents flow; in this way the magnetic field might control the rate at which warmer water is transported northwards, and also the flow of colder water from northern regions to the south - and thereby have an effect on local temperatures.