"and the princess played the clavichord"

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.

The British Clavichord Society's website.