  Resonant Bragg diffraction of soft, circularly polarized x-rays has been used
to observe directly the temperature dependence of chiral-order melting in a
motif of Mn ions in terbium manganate. The underlying mechanism uses the b-axis
component of a cycloid, which vanishes outside the polar phase. Melting is
witnessed by the first and second harmonics of a cycloid, and we explain why
the observed temperature dependence is different in the two harmonics. Our
direct observation of melting is supported by a solid foundation of evidence,
derived from extensive studies of the azimuthal-angle dependence of intensities
with both linear and circular polarization.
