  Pressure, compressibility, and Hall conductance of anisotropic states at
higher Landau levels are computed. Pressure and compressibility become
negative. Hall conductance is unquantized and varies with filling factor. These
facts agree with the recent experimental observations of highly anisotropic
compressible states at higher Landau levels. It is shown, as an implication of
negative pressure, that the quantum Hall effect has extraordinary stability,
that is, Hall resistance is quantized even when the longitudinal resistance
does not vanish.
