KONVEKTIVNAYA NEUSTOICHIVOST' FERROZHIDKOSTI.

Conditions are clarified under which there occurs instability of the equilibrium of a nonuniformly heated ferrofluid in a gravitational field and a nonuniform magnetic field. The latter is, first, the cause of Archimedes lifting forces and, secondly, magnetic intensity gradients bring about the appearance of internal heat sources (the magnetocaloric effect). As a rule, this effect is extremely weak and its correct evaluation requires that liquid compressibility be simultaneously taken into account in the heat conductivity equation. It is shown that it is precisely due to the neglect of compressibility that the mistaken conclusion regarding the convective instability of isothermal ferroliquids, contradicting the laws of thermodynamics, was drawn by B. M. Berkovskiy in his works. A non-dimensional criterion characterizing the stability of ferrofluid equilibrium is formulated. In the limit cases of large or small cavities, this criterion passes into ferrohydrodynamic analogs of the usual Schwartzschild or Raleigh criteria.