An apparatus is described in which a pure dynamic shear strain is produced in a small sample of liquid or other material, and the resulting shear stress is measured in the frequency range between 20 and 1000 cps. The shear stress is decomposed into its real and imaginary parts, which yield the shear rigidity and the shear viscosity. Design and working equations are derived. Two liquids are investigated and the data shown. The effect of impurity molecules is discussed, and a possible application to lubrication theory is suggested.