  The problem of finding boundary conditions for fastening of a ring membrane,
which are inaccessible for direct observation from the natural frequencies of
its flexural oscillations, is considered. Two theorems on the uniqueness of
this problem are proved, and a method for establishing the unknown conditions
for fastening of the membrane to the walls is indicated. An approximate formula
for determining the unknown conditions is obtained, using first three natural
frequencies. The method of approximate calculation of unknown boundary
conditions, is explained with the help of an example. Keywords: Boundary
conditions, inverse spectral problem, membrane, natural frequencies, Plucker
coordinates, Plucker relation.
