A stable dc supercurrent with an extended negative-resistance region has been observed in the I-V characteristics of very small Josephson tunnel junctions. This supercurrent and its response to external noise are in accord with recent theoretical predictions of Ivanchenko and Zil'berman.

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An experimental study has been made of the Riedel singularity in Sn-Sn-oxide-Sn Josephson tunnel junctions. The data indicate that gap anisotropy rather than quasiparticle damping is the dominant factor in rounding off the observed singularity. However, it appears feasible to use the singularity as a probe of quasiparticle damping effects.A new experimental configuration has been discovered in which motion of the superconducting domain structure can be realized under ideal conditions. The measured spatial periodicity of the moving structure in tin corresponds closely to the predictions of the Landau model.

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