We have seen that an electric current is really a flow of electrons. Now
an electric current exhibits a magnetic effect. The surrounding space is
endowed with energy which we call electro-magnetic energy. A piece of
magnetised iron attracting other pieces of iron to it is the popular
idea of a magnet. If we arrange a wire to pass vertically through a
piece of cardboard and then sprinkle iron filings on the cardboard we
shall find that, on passing an electric current through the wire, the
iron filings arrange themselves in circles round it. The magnetic force,
due to the electric current, seems to exist in circles round the wire,
an ether disturbance being set up. Even a single electron, when in
movement, creates a magnetic "field," as it is called, round its path.
There is no movement of electrons without this attendant field of
energy, and their motion is not stopped until that field of energy
disappears from the ether. The modern theory of magnetism supposes that
all magnetism is produced in this way. All magnetism is supposed to
arise from the small whirling motions of the electrons contained in the
ultimate atoms of matter. We cannot here go into the details of the
theory nor explain why, for instance, iron behaves so differently from
other substances, but it is sufficient to say that here, also, the
electron theory provides the key. This theory is not yet definitely
_proved_, but it furnishes a sufficient theoretical basis for future
research. The earth itself is a gigantic magnet, a fact which makes the
compass possible, and it is well known that the earth's magnetism is
affected by those great outbreaks on the sun called sun-spots. Now it
has been recently shown that a sun-spot is a vast whirlpool of electrons
and that it exerts a strong magnetic action. There is doubtless a
connection between these outbreaks of electronic activity and the
consequent changes in the earth's magnetism. The precise mechanism of
the connection, however, is still a matter that is being investigated.