check this website out
http://en.wikipedia.org/wiki/Einstein
Einstein's third paper that year, "On the Electrodynamics of Moving
Bodies" ("Zur Elektrodynamik bewegter Körper"), was published in
September 1905. This paper introduced the special theory of
relativity, a theory of time, distance, mass and energy which was
consistent with electromagnetism, but omitted the force of gravity.
While developing this paper, Einstein wrote to Mileva about "our
work on relative motion", and this has led some to ask whether
Mileva played a part in its development. Some believe that Einstein
and his wife were both aware of Henri Poincare's publishing of
Relativity just a few weeks before Einstein. [See Henri Poincare
and also http://www.xtxinc.com] However, his colleagues would say
that he "thought much and read little."
A fourth paper, "Does the Inertia of a Body Depend Upon Its Energy
Content?", ("Ist die Trägheit eines Körpers von seinem
Energieinhalt abhängig?") published late in 1905, showed one
further deduction from relativity's axioms, the famous equation
that the energy of a body at rest (E) equals its mass (m) times the
speed of light (c) squared: E = mc2 .
