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CHAPTER III
ELECTRONS AND X RAYS
As our story approaches the subjects of electric lighting,
X rays, and wireless, we come into the field of the play of
molecules, atoms, and electrons. These structures are
invisible even with the most powerful microscopes. Never-
theless, Sir J. J. Thomson, Lord Rutherford of Nelson, and
their colleagues of the Cavendish Laboratory at Cam-
bridge, England, by their ingenious experiments, have
prepared a way into this enticing domain, into which
many other physicists in Europe and America have
pressed onward during the last 30 years.
We all know of matter in three states, gaseous, liquid,
and solid, as, for instance, air, water, and copper. Long
ago it was found that many solids could be melted into
liquids, and liquids changed into gases, if only they are
heated to suitable temperatures. In the case of water,
summer temperatures suffice to melt winter's ice into
liquid water, and the cook-stove turns water plentifully
into steam. What we see and call steam, to be sure, is
but a cloud of liquid water drops, similar to the fleecy
clouds in the atmosphere. Real steam is invisible, like air
itself. It occurs in the little, apparently vacant space just
in front of the end of the spout of a boiling teakettle.
Gases, such as air, hydrogen, oxygen, nitrogen, and the
rest, behave very differently at atmospheric pressure and
in vacua. For instance, at atmospheric pressure they
strongly resist the flow of electricity, unless their resis-
tance is broken down by high voltages, as in lightning
flashes, the spark, and the arc. But when the pressure is
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