Earlier papers have described a technique whereby a stratified shear flow may be produced under controlled conditions in the laboratory. A comparison between the experiments and theory is made here for small-amplitude unstable disturbances in an accelerating stratified free shear layer at the diffuse interface between layers of brine and water. In the early stages of the observed growth of the instability, which takes the form of growing waves, three measurable quantities can be compared with predicted values: the wavelength of the small amplitude waves, the time, which determines the flow conditions, and the growth rates of the waves. Some observations of the development of the disturbances to finite amplitude, the transition to turbulence and the resulting turbulence are reported.