"A Secret Frozen in Time" by Shunrō Oshikawa

Summary

Shunrō Oshikawa (1876-1914) was one the two most important founders of Japanese science fiction (the other being Unno Juza, 1897-1949). This story is a charming tribute to all those engaged in historical research. A young Portuguese child discovers an empty beer bottle on a beach. Her father, a well known scientist, discovers a message inside that may solve one of the greatest mysteries in the West African chronicles. 

This is a radio version, and not a translation. It has been adapted for historyradio.org by Michael Henrik Wynn, and he also plays the part of the traveler.