If two solids are coupled to each other through a liquid layer, transverse slip can occur at the boundary surface when an elastic wave is incident on the boundary. Algebraic expressions for the amplitudes of the various wave modes are derived on the assumption of transverse slip at the boundary, and these are compared with wave mode amplitudes for a solid‐air boundary. Experimental measurements in connection with the design of an indicator for the degree of coupling between an angle probe and a test object are explained on this assumption. Curves are given showing wave‐mode amplitude for: (i) Plexiglas‐air boundary; (ii) Plexiglas steel boundary assuming transverse slip; (iii) Plexiglas steel boundary assuming rigid contact.