amount of force required to overcome the inertia of a body
is proportionate to its mass. So that if the mass of a body is doubled,
then twice the force would be required to move it, while if the body
were halved, half the force would suffice to do it.

Inertia is possessed quite as much by a moving body as a body at rest.
The definition given points this out, as it states that matter cannot of
itself change its state of motion. If a body therefore is in motion, it
requires a certain amount of resistance to bring the body to a state of
rest, or the loss of an equal amount of energy, by friction or
otherwise, equal to the quantity which it absorbed in order for it to be
set in motion.

We get numerous examples of this property of the inertia of bodies in
our daily experience. Many of the accidents that befall people in
various ways are due to this property of the inertia of matter. A
cyclist is riding a machine down-hill, and loses control over his
machine, with the result that he runs into a wall, and is killed. Now
what has happened? The cyclist has participated in the motion of the
machine, with the result that when the machine has been suddenly
stopped, the body has been thrown forward owing to the momentum it had
acquired.

We are constantly being affected by the property of inertia of matter,
in tram and train and bus. Whenever any of these are suddenly stopped,
or suddenly started, we are thrown either backward or forward, owing to
the body either not having acquired the motion of the train, or, having
acquired it, is unable to lose its motion as quickly as the train, and
is therefore thrown forward.

CHAPTER IV

AETHER IS MATTER

ART. 42. _Aether is Matter._--The hypothesis of an Aether which fills
all space was made in order that scientists might be able to account for
certain phenomena of Light, which otherwise were difficult to account
for. Its existence is demanded not only for the phenomena of Light, and
Heat, but, in view of the comparatively recent researches of Hertz on
"Electric Waves," of Electricity also.

The Aetherial Medium is generally assumed to be that fundamental medium,
by means of which possibly all the properties of matter, and all the
phenomena of motion of the universe are to be explained. Light and Heat
have been proved to be due to the periodic wave-motion of this universal
Aether, while from the investigations and