The clavichord is a keyboard instrument dating from the fourteenth century. Its popularity was at its height from the sixteenth to the eighteenth centuries; it appears in compositions from the Renaissance, Baroque and Classical periods. It produces sound by means of keys attached to metal blades (tangents) which strike brass or iron strings. Because the sound it produces is relatively quiet, it was often used as a practice instrument. Princess Marya's playing would not have disturbed her father's rest.
František Xaver Dušek (1731-1799) was a Czech musician and composer known for his abilities with keyboard instruments such as the piano and the harpsichord. He was friends with Mozart, and taught Mozart's son Karl Thomas to play the piano.
He was a capable military leader, serving in the Russo-Turkish War where he became Major-General of the cavalry; but he is now best known for his political role. The idea of "Potemkin villages" came about after one of Catherine's tours of southern Russia, where Potemkin was the governor. Potemkin is accused of having set up fake villages along the Catherine's route in order to make the south appear more prosperous than it really was. However, this is probably false. Contemporary witnesses countered these allegations, and such a massive fraud would have been incredibly difficult to pull off convincingly.
In 1900 the Russian navy launched a battleship called Potemkin. In 1905, during the first revolution, the crew of this ship mutineed. The rebellion was later portrayed in Sergei Eisenstein's famous 1925 film The Battleship Potemkin.