ion. So, matter can change in going from solids to liquids
and gases, or _vice versa_. The behavior of atoms in the process is
surpassingly interesting.

Gold changes its density, and therefore its thickness, between the two
dies of the mint that make it money. How do the particles behave as
they snuggle up closer to each other?

Take a piece of iron wire and bend it. The atoms on the inner side
become nearer together, those on the outside farther apart. Twist it.
The outer particles revolve on each other; those of the middle do not
move. They assume and maintain their new relations.

Hang a weight on a wire. It does not stretch like a rubber thread, but
it stretches. Eight wires were tested as to their tensile strength.
They gave an average of forty-five pounds, and an elongation averaging
nineteen per cent of the total length. Then a wire of the same kind
was given time to adjust itself to its new and trying circumstances.
Forty pounds were hung on one day, three pounds more the next day, and
so on, increasing the weights by diminishing quantities, till in sixty
days it carried fifty-seven pounds. So it seems that exercise
strengthened the wire nearly twenty-seven per cent.

While those atoms are hustling about, lengthening the wire and getting
a better grip on one another, they grow warm with the exercise. Hold a
thick rubber band against your lip--suddenly stretch it. The lip
easily perceives the greater heat. After a few moments let it
contract. The greater coldness is equally perceptible.

A wire suspending thirty-nine pounds being twisted ninety-five full
turns lengthened itself one sixteen-hundredth of its length. Being
further twisted by twenty-five turns it shortened itself one fourth of
its previous elongation. During the twisting some sections took far
more torsion than others. A steel wire supporting thirty-nine pounds
was twisted one hundred and twenty times and then allowed to untwist at
will. It let out only thirty-eight turns and retained eighty-two in
the new permanent relation of particles. A wire has been known to
accommodate itself to nearly fourteen hundred twists, and still the
atoms did not let go of each other. They slid about on each other as
freely as the atoms of water, but they still held on. It is easier to
conceive of these atoms sliding about, making the wire thinner and
longer, when we consider that it is the opinion of our best physicists
that molecules made of