  Direct means of measuring the susceptibility towards an octupole order
parameter are proposed via a sixth-rank tensor property. Equivalent derivatives
of more conventionally measured tensor properties, including elastic stiffness,
magnetic susceptibility, and elastoresistivity, are written in full, as
constrained by the symmetry of the experimentally-motivated $O_h$ point group.
For simplicity, we consider the specific case of $Pr^{3+}$ ions in a cubic
point symmetry with a $\Gamma_3$ crystal field ground state, but the ideas are
somewhat general. Experimental feasibility of measuring these various
derivatives of tensor quantities is discussed.
