  We report direct observation of long-term durability of superconductivity of
several YBa$_2$Cu$_3$O$_7$-Ag$_2$O composites that were first prepared and
studied almost 14 years ago [J. J. Lin {\it et al}., Jpn. J. Appl. Phys. {\bf
29}, 497 (1990)]. Remeasurements performed recently on both resistances and
magnetizations indicate a sharp critical transition temperature at 91 K. We
also find that such long-term environmental stability of high-temperature
superconductivity can only be achieved in YBa$_2$Cu$_3$O$_7$ with Ag$_2$O
addition, but not with pure Ag addition.

Superconductivity;Materials Science