DOC.
71
PRINCETON LECTURES
353
THE GENERAL
THEORY
velocity
of
light
is characterized,
according to
(106), by
the
equation
(1
+
k/4x
f
adV0/r)
(dx12
+
dx22
+
dx32)
The
velocity
of
light
L,
is
therefore
expressed
in
our co-
ordinates
by
(107)
Vdx12
+
dx22
+
dx32
k
Í
adV0
dl
=
1
-
4tt
J
/r [111]
We
can
therefore draw the
conclusion
from
this,
that
a
ray
of
light
passing
near a
large
mass
is
deflected. If
we
imagine
the
sun,
of
mass
M,
concentrated
at
the
origin
of
our
system
of
co-ordinates,
then
a
ray
of
light,
travelling
parallel to
the
x3-axis,
in
the
x1
-
x3
plane,
at
a
distance
A from
the
origin,
will be
deflected,
in
all, by
an amount
[112]
a
=
f
+
1/L
dL/dx1 dx3
towards
the
sun.
On
performing
the
integration
we
get
(108)
kM
a
=
2XA.
The
existence of this
deflection,
which
amounts to
1.7"
for A
equal
to
the
radius
of
the
sun,
was
confirmed,
with
remarkable
accuracy,
by
the
English
Solar
Eclipse
Expedi-
tion in
1919,
and
most
careful
preparations
have
been
made
to get
more
exact
observational data
at
the solar
eclipse
in 1922. It
should be
noted that
this
result,
also,
of the
theory
is
not
influenced
by our
arbitrary
choice of
a
system
of
co-ordinates.
[113]
[93]