  An experiment is proposed to measure the out-of-equilibrium splitting of the
Kondo resonance in an ultrasmall quantum dot, by adding a third, weakly coupled
lead to the standard two-lead quantum-dot system, and sweeping the chemical
potential of that lead. Fixing the voltage bias between the source and drain
leads, we show that the differential conductance for the current through the
third lead traces the out-of-equilibrium dot density of states (DOS) for the
two-lead system. This enables one to measure the dot DOS in the presence of an
applied voltage bias. We show that this method is robust, and extends also to
the case where the coupling to the third lead is no longer weak.
