  We discuss the directional motion of an elastic three-sphere micromachine in
which the spheres are in equilibrium with independent heat baths having
different temperatures. Even in the absence of prescribed motion of springs,
such a micromachine can gain net motion purely because of thermal fluctuations.
A relation connecting the average velocity and the temperatures of the spheres
is analytically obtained. This velocity can also be expressed in terms of the
average heat flows in the steady state. Our model suggests a new mechanism for
the locomotion of micromachines in nonequilibrium biological systems.
