THERE is no such thing as _cold_. When we call a thing cold we only
mean it has but little heat in it, for everything, even _ice_, has some
heat in it.
We can readily measure the amount of heat in different things, and we
know a great deal about how it acts, but we really do not know what it
is. Heat is never _by itself_, but always with something else. We may
have hot water, we may have hot iron, but no one has ever been able to
divide the heat from the water or iron, and keep it divided.
We can easily make heat pass from one thing into another, but when
things which have different amounts of heat are put together the heat
will spread itself around so as to make all of the same temperature. A
piece of iron put into fire becomes hot, because the warmth passes from
the fire into the iron until both have the game amount of heat.
Most of the heat in the world comes from the sun. We can set fire to
things by gathering the sun's rays and bringing them to a point with a
lens.
Ice, you well know, "is water in a solid state. It is formed under the
influence of extreme cold. It is a nearly solid, transparent, brittle
substance, of a crystalline structure. It melts into water at the
temperature of thirty-two degrees Fahrenheit."
In hot countries ice is made in a machine worked on philosophic
principles.--_Selected._