ABSTRACT
In describing the macroscopic properties of a piece
of material, we are concerned with quantities such as total
mass, total energy, total magnetic moment, and other
totals of the constituent’s partic les. For homogeneous
materials, it is convenient to divide these quantities by the
volume V of the m ateria l to obtain the mass density, the
energy density, the magnetization, etc. , which we shall
subsequently re fer to as mechanical var iab les . There are
other examples of important mechanical variables which
are less familiar and not so easily defined or visualized as
those just mentioned. Some important examples are quan-
tum amplitudes of Bose fluids, staggered magnetization of
antiferromagnets, Four ier components of atom density in
a crystal, etc.
