122
DOC.
2 RELATIVITY
AND
ITS CONSEQUENCES
order
are
considered-that
the
length
of the
body
is
diminished in
that direction
in
the
ratio
1
:
1-f
N
c2
.
This
hypothesis
succeeded,
in
effect,
in
eliminating
the
disagreement
between
theory
and
experiment.
But the
theory
did not
offer
an
intellectually very satisfying
whole.
It
was
based
on
the
existence
of
an
ether that
one
had
to conceive
as
being
in
motion
with
respect
to
the
earth,
with
the
consequences
of
this
motion forever
unverifiable
by
experiment;
this
peculiarity
could
only
be
explained by
introducing
a
priori
implausible
hypotheses
into the
theory.
Could
one
really
believe
that,
by a
curious
accident,
the
laws
of
nature
present
themselves to
us
in such
a highly
unusual
way
that
none
of
them allows
us
to know
about the
fast
motion of
our
planet through
the ether?
Is it not
more
plausible
to
assume
that
some wrong or
defective
argument
had
led
us
to
this
impasse?
Before
explaining
how
these
difficulties
were
overcome,
we
will show
that
even
in
particular cases,
the
theory
based
on
the
existence
of the ether
does
not
always
offer
an
intellectually satisfying explanation
of the
phenomena,
even
though
that
representation
is
not in
direct
conflict with
experiment.
Let
us
consider,
for
example, a magnetic
pole
moving
with
respect
to
a
closed circuit.
If the
number of
lines
of
force
that
cross
the
surface
enclosed
by
the
circuit
changes
with
time, a
current will
be
generated
in
the conductor.
As
we
know,
the
generated
current
depends only on
the
rate
of
change
of
the flux
that
crosses
the
circuit. This rate
depends
only
on
the
relative motion
of the
pole
with
respect
to
the
circuit;
in
other
words,
from
the
point
of
view
of
the
result
produced,
it
does
not
make
any
difference whether
it
is
the
circuit
that
moves,
while
the
pole is
at rest,
or
whether the
opposite
is
the
case.
But
to
understand this
phenomenon
from the
point
of
view
of the ether
theory,
one
must
attribute
fundamentally differing
states to
the
ether, depending
on
whether
it
is
the
pole
or
the
circuit
that
is
moving
with
respect
to
the ether. In the
first
case
one
must
consider
that the motion of the
pole
has
the
effect
of
changing
the
strength
of the
magnetic
field
at
the
various
points
of the ether
at each
instant of
time.
The
change
thus
engendered
produces
an
electric
field with closed lines
of
force,
the
existence
of
which
is independent
of the
presence
of the
circuit. This
field,
like
every
field
of
electrical
force,
possesses a
certain
energy;
it
is
this field
that
produces
the electric
current in
the
circuit.
If,
in
contrast,
it is
the
circuit
that
is
in
motion
while
the
pole
remains
at
rest,
then
no
electric
field will
be
generated.
In that
case,
the electrons
present
in
the conductor
are subjected
to
ponderomotive
forces
arising
from the motion of the electrons in
the
magnetic
field,
forces
that make the electrons
travel,
thus
producing
the induced electric
current.
Thus,
in
order for them
to
be understood
with
the
aid
of the ether
theory,
two
experiments
that
are
not
essentially
different
in themselves
require
that
substantively
different
states be
attributed
to
the ether.
Moreover, such
a split,
alien to
the
nature
of
[9]