The concept of the magnetic pole originated in the work of Gilbert in 1600 and by mid 19th century Coulomb observed a force law between magnetic poles perfectly equivalent to his celebrated law of force between electric charges. But by the late 19th century the work of Maxwell and Ampere had established the impossibility of separating the north and south poles of a magnet to produce free magnetic charges or monopoles.
Following the arguments of Dirac, in the twentieth century, it was recognised that magnetic monopoles can exist as elementary particles, but this did not revise the widespread belief that Coulomb's magnetic charge, as it occurs in condensed matter, cannot not be separated into monopolar form.
In this talk I shall describe recent experiments that prove that conventional magnetic charge in solids can in fact be separated into freely moving magnetic monopoles - atom sized packets of magnetic charge that may even form currents analogous to electrical currents - so called "magnetricity". This remarkable phenomenon occurs in a class of material called "spin ice". I will
show how the conduction of magnetic charges in spin ice is equivalent to the conduction of electric charge in weak electrolytes and will demonstrate how this analogy enabled us to quantitatively measure the elementary magnetic charge [1].
