Romans had discovered that the lodestone would attract iron, though a
stone wall intervened. They were fond of mounting a bit of iron on a
cork floating in a basin of water and watch it follow the lodestone
held in the hand. It is related that the early magicians used it as a
means of transmitting intelligence. If a needle were placed upon a bit
of cork and the whole floated in a circular vessel with the alphabet
inscribed about the circle, one outside the room could cause the
needle to point toward any desired letters in turn by stepping to the
proper position with the lodestone. Thus a message could be sent to
the magician inside and various feats of magic performed. Our own
modern magicians are reported as availing themselves of the more
modern applications of electricity in somewhat similar fashion and
using small, easily concealed wireless telegraph or telephone sets for
communication with their confederates off the stage.

The idea of encircling a floating needle with the alphabet was
developed into the sympathetic telegraph of the sixteenth century,
which was based on a curious error. It was supposed that needles which
had been touched by the same lodestone were sympathetic, and that if
both were free to move one would imitate the movements of another,
though they were at a distance. Thus, if one needle were attracted
toward one letter after the other, and the second similarly mounted
should follow its movements, a message might readily be spelled out.
Of course the second needle would not follow the movements of the
first, and so the sympathetic telegraph never worked, but much effort
was expended upon it.

In the mean time others had learned that many substances besides
amber, on being rubbed, possessed magnetic properties. Machines by
which electricity could be produced in greater quantities by friction