The Fourier transform of a linear response function gives a “generalized” form of this quantity whose imaginary and real parts are related by the Kramers–Krönig relations. This quantity’s magnetic form can be measured with a torsional balance named for Evans. In ferromagnetic crystals, this quantity is a tensor of the partial derivatives of the i-th component of M with respect to the j-th component of H. The temperature dependence of this quantity above the Curie temperature is described by the (*) Curie-Weiss law. This quantity's “electric” form is the constant of proportionality between a material’s polarization and the external E-field, and equals the dielectric constant minus one. For 10 points, name this quantity symbolized chi that describes a material’s response to external electric or magnetic fields. ■END■ (10[1])