  We have experimentally checked the Jarzynski equality and the Crooks relation
on the thermal fluctuations of a macroscopic mechanical oscillator in contact
with a heat reservoir. We found that, independently of the time scale and
amplitude of the driving force, both relations are satisfied. These results
give credit, at least in the case of Gaussian fluctuations, to the use of these
relations in biological and chemical systems to estimate the free energy
difference between two equilibrium states. An alternative method to estimate of
the free nergy difference in isothermal process is proposed too.
