  We introduce a calorimetric approach to probe persistent currents in normal
metal rings. The heat capacity of a large ensemble of silver rings is measured
by nanocalorimetry under a varying magnetic field at different temperatures (60
mK, 100 mK and 150 mK). Periodic oscillations versus magnetic field are
detected in the phase signal of the temperature oscillations, though not in the
amplitude (both of them directly linked to the heat capacity). The period of
these oscillations ($\Phi_0/2$, with $\Phi_0 = h/e$ the magnetic flux quantum)
and their evolution with temperature are in agreement with theoretical
predictions. In contrast, the amplitude of the corresponding heat capacity
oscillations (several $k_{\mathrm{B}}$) is two orders of magnitude larger than
predicted by theory.
