Evening star. [volume] (Washington, D.C.) 1854-1972, 1914-01-04

L huge bathrobe, seized paperwe1ght
| and beat tattoo on the steam radiator.
The signal was readily interpreted by the
| ianitor in the basement as hurry call for
more heat, and soon the man, throwing
aside his bathrobe, turned to his reading and
| forgot that there was any such thing as heat
in the world.
What is this thing we call heat2 Does
the hot steam pipe pour out an invisible
fluid that warns the air in the room, or is
it another mysterious force, like electricity,
that cannot be explained by human intelli-
genceo
Neither. To explain heat it is necessary to
imagine everything as composed of mole
cu1es, which in turn are made up of atoms,
and this whole mass of particles in violent
vibratory motion. Increasing the motion of
the atoms increases the temperature of the
mass, and decreasing this motion lowers the
temperature. When iron is very cold the
atoms and molecules, move comparatively
slow, and when it is whitehot the atoms
move so fast that they jostle one another
apart and som begin to Follower one another,
and the melting iron flows like water.
Heat is derived from the sun, either from
the sun direc. or from the suns energy
stored in coal or wood. But heat can also
be derived from mechanical energy and from
electrical energy. Heat is generated when
a penny is rubbed on the carpet, when nail
is struck by hammer, when two pieces of
wood are rubbed together. By rubbing two
pieces of ice together they may be melted,
though the temperature be far below freezing.
TT was generally believed, up to the nine
tenth century, that heat was a substance
devoid Of weight and diffused throughout
the great mass of all things. This hypotheti
cal substance was called caloric. When
Davy proved that he could produce heat by
mechanical energy the old caloric theory
was hurriedly abandoned.
Scientists are practically agreed that
hot body differs from cold body in that
the very small particles, or molecules, of
which it is composed are in state of rapid
to-and-fro motion or oscillation. Increasing
the temperature serves only to increase the
violence of these molecular vibrations until
the body is melted down or evaporated.
When body is deprived of all its heat the
oscillations cease entirely. If the sun heat
should suddenly fail, the temperature of the
zero, or four hundred and fifty-nine degrees
below zero, Fahrenheit, at which point the
molecules of all materials are motionless.
Therefore, it becomes apparent that work,
or energy, must be communicated to the
molecules before the oscillations can be pro-
duced. If a body is warmed at the fire, the
heat energy is transmitted to it. If two
pieces of steel are heated by friction, work
is done on the molecules by the application
of power. Energy can never be destroyed:
it can only be changed in form. We say en-
ergy is lost when it is spread out so thin"
that it cannot be utilized.
These molecules that ere in violent agi
tation are extremely minute, but have a
definite size and weight for each substance.
A molecule of water, it has been figured, has
diameter of about one fve-ten- thousandths
of an inch. Though these molecules are
very small in size, their velocity, even at
ordinary low temperatures, is very great.
In air at the freezing point they oscillate
back and forth at the astonishing rate of
fourteen hundred and seventy feet second.
The average length of their path, between
oscillations, is about one two-hundred- and
seventy seven thousandths of an inch, and
the number of these dancing molecules in
cubic inch of air is about one sextillion.
Each of the molecules moves back and forth
at terrific speed, colliding with its fellows
at the rate of five thousand million times
second.
THE molecules of every substance attract
one another with force called cohesion.
1t is this cohesion that prevents string or a