  Expressions are given for the maximum and minimum values of Poisson's ratio
$\nu$ for materials with cubic symmetry. Values less than -1 occur if and only
if the maximum shear modulus is associated with the cube axis and is at least
25 times the value of the minimum shear modulus. Large values of $|\nu|$ occur
in directions at which the Young's modulus is approximately equal to one half
of its 111 value. Such directions, by their nature, are very close to 111.
Application to data for cubic crystals indicates that certain Indium Thallium
alloys simultaneously exhibit Poisson's ratio less than -1 and greater than +2.
