n
the threads together they fly apart and refuse to join up the minute
hooks with which the wool fibres are furnished. The spinning operation
would come to an end were there not means provided by which the air can
be so filled with moisture that the fibres become damp and the action
ceases. So in some cases a stream of air filled with positive and
negative ions is made to play upon the fibres; the fibres select what
ions they want, and so neutralizing themselves, spinning can proceed
again.

When a current of electricity runs along a wire there is in fact nothing
more than a procession of electrons. The stream of electrons that runs
through the filaments in the lamps that light this room, raising the
filaments to a white heat, are set in motion by the dynamos in the city.
There is a complete wire circuit, including the dynamo, the conductors,
and the lamps. When the dynamos are not working the electrons do not as
a whole move either way, though they are always there. When the dynamo
begins to turn, the electrons set out on their continuous journey.

Electrons are involved in the emission of wireless signals, and in their
receipt. The so-called 'valve', which multiplies minute electric signals
and was so greatly improved during the war, depends entirely on the
action of electrons, and the brilliant experimental work was based on
the newly-acquired knowledge of their properties.

I have told you that under certain circumstances a stream of electrons
may generate X-Rays, in reality a form of light rays. This action is a
very common one, and it is curious that the faster the electron goes the
shorter is the wave-length of the radiation. A very fast electron
generates an X-Ray of so short a wave-length that the penetrating power
of the ray, which goes with the shortness of the wave, is excessive, and
in this way we may have rays which go right through the human body or
even through inches of steel. As the speed of the exciting electron
becomes less, the X-Rays are less penetrating. With still slower
electrons we may generate ordinary light, and it will take a slower
electron to generate red than to generate blue. The slowest electrons we
use in this way have a speed of many hundred miles per second; the
fastest have a speed which nearly approaches that of light, or 186,000
miles a second.

And conversely radiation can set electrons in motion. When X-Rays are
driven into a patient's body electrons are set in motion within