and drink. But these
emanations and solutions that affect our senses probably do not
represent a chemical division of matter; when we smell an apple or a
flower, we probably get a real fragment of the apple, or of the flower,
and not one or more of its chemical constituents represented by atoms or
electrons. A chemical analysis of odors, if it were possible, would
probably show the elements in the same state of combination as the
substances from which the odors emanated.

The physicists herd these ultimate particles of matter about; they have
a regular circus with them; they make them go through films and screens;
they guide them through openings; they count them as their tiny flash is
seen on a sensitized plate; they weigh them; they reckon their velocity.
The alpha-rays from radio-active substances are swarms of tiny meteors
flying at the incredible speed of twelve thousand miles a second, while
the meteors of the midnight sky fly at the speed of only forty miles a
second. Those alpha particles are helium atoms. They are much larger
than beta particles, and have less penetrative power. Sir J. J. Thomson
has devised a method by which he has been able to photograph the atoms.
The photographic plate upon which their flight is recorded suggests a
shower of shooting stars. Oxygen is found to be made up of atoms of
several different forms.

III

The "free path" of molecules, both in liquids and in gases, is so minute
as to be beyond the reach of the most powerful microscope. This free
path in liquids is a zigzag course, owing to the perpetual collisions
with other molecules. The molecular behavior of liquids differs from
that of gases only in what is called surface tension. Liquids have a
skin, a peculiar stress of the surface molecules; gases do not, but tend
to dissipate and fill all space. A drop of water remains intact till
vaporization sets in; then it too becomes more and more diffused.

When two substances combine chemically, more or less heat is evolved.
When the combination is effected slowly, as in an animal's body, heat is
slowly evolved. When the combustion is rapid, as in actual fire, heat is
rapidly evolved. The same phenomenon may reach the eye as light, and the
hand as heat, though different senses get two different impressions of
the same thing. So a mechanical disturbance may reach the ear as sound,
and be so interpreted, and reach the hand as motion in matter. In
combustion, the oxygen combines rap