232
NEW
TEST
OF
RELATIVITY
Doc.
41
ON
THE
POSSIBILITY
OF
A
NEW
TEST
OF
THE
RELATIVITY
PRINCIPLE
by
A.
Einstein
[Annalen
der
Physik
23 (1907):
197198]
In
an
important
paper
published
last
year,
Mr.
J.
Stark1
demonstrated
that
the
moving
positive ions of
canal
rays
emit
line
spectra
by
identifying
the
Doppler
effect
and
following
it quantitatively.
He
also undertook
experiments
with the intention
of detecting and
measuring
an
effect of the
second
order (proportional
to (v/V)2);
however,
the
experimental
arrangement,
which
was
not set
up
specifically for this
purpose,
was
not adequate
for
achieving
reliable results.
I will
show
here
briefly
that the
principle
of
relativity
in conjunction
with the
principle
of the constancy of the
velocity
of light
makes
it possible
to
predict the
above
effect.
As
I
showed
in
an
earlier
paper2,
it follows
from
these principles that
a
uniformly
moving
clock
runs
at
a
slower
rate
as
judged
from
a
"stationary"
system
than
as judged
by
a comoving
observer. If
v
denotes the
number
of
the clock's strokes
per
unit time for the observer
at
rest, and
v0
the
corresponding number
for the
comoving
observer,
then
[3]
or
to
first
approximation
v
V
1

V0
J
v

v
Ü 
_
i
1
v
"o
2
V
The atom
ion
of
the canal
rays
that emits
and
absorbs radiation
of
certain
frequencies
is thus
to
be
conceived
as
a
fastmoving
clock, and the relation
just indicated
can
therefore
be
applied to
it.
[1]
[2]
1J.
Stark,
Ann.
d.
Phys. 21
(1906): 401.
2A.
Einstein,
Ann. d.
Phys.
17
(1905): 903.