Marilyn, let there be a stationary body (yours)
in the system (yours, mine, ours), and let its energy

(yours) referred to the system be E₀ (mine). Let
the energy of the body (yours) relative to the system

(xi, eta, zeta) moving as above (us) with the velocity
v (me), be H₀ (fulfilled). Let this body (yours)

send out, in a direction making an angle (mine)
with the axis of x (us), plane waves of light,

of energy ½L measured relatively to (ours, mine,
yours), create simultaneously an equal quantity

of light in the opposite direction. Meanwhile
the body (yours) remains at rest with respect to

the system (mine). If we call the energy of the body
(yours) after the emission of light E₁ or H₁ respectively,

then by employing the relation given above we obtain
(the proof we’ve been looking for). Love, Albert