  The secular equation for surface acoustic waves propagating on a monoclinic
elastic half-space is derived in a direct manner, using the method of first
integrals. Although the motion is at first assumed to correspond to generalized
plane strain, the analysis shows that only two components of the mechanical
displacement and of the tractions on planes parallel to the free surface are
nonzero. Using the Stroh formalism, a system of two second order differential
equations is found for the remaining tractions. The secular equation is then
obtained as a quartic for the squared wave speed. This explicit equation is
consistent with that found in the orthorhombic case. The speed of subsonic
surface waves is then computed for twelve specific monoclinic crystals.
