428 DOC.
45 ON THE INERTIA OF ENERGY
[9]
About the time
of
this
paper,
Einstein had
an
extensive
correspondence
with Wien and
Sommerfeld
on
the
possibility
of
transmitting
signals
at
superluminal
velocities. For
a
discus-
sion
of
this
correspondence, see
Vol.
5,
the edi-
torial note,
"Einstein
on
Superluminal Signal
Velocities."
[10]
Two
arguments against
the
possibility
of
superluminal
velocities for
an
electron
are given
in
Einstein 1905r
(Doc. 23), pp.
906,
920.
[11]
This is
Einstein's
first
use
of
the
phrase
"the
equivalence
of
mass
and
energy."
Earlier,
he had stated that the
inertia
or mass
of
a body
depends on, or
is
a measure of,
its
energy con-
tent
(see
Einstein 1905v
[Doc. 27],
Einstein
1906e
[Doc. 35]).