162 DOC. 38 ETHER AND RELATIVITY
4
SIDELIGHTS
ON
RELATIVITY
mutual
actions
than
those of immediate
contact,
e.g.
the
communication of motion
by impact,
push
and
pull, heating
or
induc-
ing
combustion
by
means
of
a
flame,
etc.
It
is
true
that
even
in
everyday
experi-
ence
weight,
which is in
a sense
action at
a
distance,
plays
a
very
important
part.
But since in
daily
experience
the
weight
of
bodies meets
us as something
constant,
something
not linked to
any
cause
which
is variable in
time
or place, we
do
not
in
everyday
life
speculate
as
to
the
cause
of
gravity,
and
therefore do not become
conscious of
its character
as
action at
a
distance.
It
was
Newton’s
theory
of
gravitation
that
first
assigned
a cause
for
gravity
by
interpreting
it
as
action
at
a
distance,
proceeding
from
masses.
Newton’s
theory
is
probably
the
greatest
stride
ever
made in
the
effort
towards
the
causal
nexus
of
natural
phenomena.
And
yet
this
theory
evoked
a lively sense
of discomfort
among
Newton’s
contempor-
aries,
because
it
seemed to be in
conflict
with
the
principle springing
from
the
rest
of
experience,
that
there
can
be
reciprocal