The Washington times., 1920-01-20
Must Be Some Comparison.

Since the time OF the ancient
Greeks 1t. has been well known that
in describing tho motion Of a body
we must refer to another body. The
motion Of q railway train is described
with reference to the ground. OF q
planet with reference to the total as
semblaee of visible fixed stars. In
physics the bodies to which motions
are specially referred are termed sys-
TENS Of coordinates. The. laws OF
mechanics of Galileo and Newton can
be formulated only by using sys.
tenn Of coordination.
Tho state Of motion Of q system OF
coordinates cannot be chosen arbt-
trarfly IL the laws of mechanics are
to hold good Ut must be free from
twisting and from acceleration). The
system of coordinates employed In
mechanics is called an inertia system
The state Of motion OF an merits
system, SO far as mechanics are con
cerned, is not restricted by nature tc
one condition. The condition in the
following proposition suffices; a sys-
tenn OF coordinates moving in the
same direction and at the same rate
Is q system OF inertia itself q sys-
tenn of inertia The special relativity
theory is therefore the application OF
the following proposition to any
natural process: "Every law Of ma
ture which holds good with respect
to a coordinate system X must also
hold good for any other system X.
provided that X and X are in uniform
movements Of translation.
Reiativity's second Prinefple.
The second principle on which the
special relativity theory rests is that
Of the constancy of the velocity OF
light in a vacuum. Light in a vacuum
has a definite and constant velocit,
independent of 1.-THE velocity of it's
source. Physicists owe their conf
dence in this proposition to the Max
well-Lorents theory OF electro-dy-
namics.
The two principles which I have
mentioned have received strong eX-
perimental confirmation, but do no.
seem to be logically compatible. Tho
special relatively theories achieved
their local reconciliation by making a
change In kinematics: that Is to say,
in the doctrine of the physical laws
of space and time. II became evident
that a statement of the coincidence OF
two events could have q meaning only
In connection with a system of CO.
ord dInat ton, that the mass of bodies
and the rate OF movement of clocks
must depend on their state of motion
with regard to the co-ordinates.
But the older physics, including the
laws OF motion of Calico and Newton,
clashed with the relativistic kline.
matics that have indicated. Tho
latter gave origin to certain general
lied mathematical conditions with
which the laws of nature would have
to conform II the two fundamental
principles were compatible. Physics
h ad to be modified. The most potable
change was a new law for motion for
(very rapidly moving mass-points
and this soon came to be verified in
the case OF electrically laden parti-
cIes. The most important result OF
the special RELATIVELY system con-
cerncd the inert mass OF a material
system.
II becomes evident that tho inertis
of such a system must depend on It's
energy-content, 30 that we were
driven TO the conception that inert
mass was nothing else than laten,
energy. The doctrine OF tho conser.
walton OF mass lost Its independence
and became merged In the dostrine
and conservation OF energy.
The special RELATIVELY theory, which
was simply a systematic extension Of
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