WHILE it is well established that solutions of macro-molecular substances may show an anomalous fall in the coefficient of viscosity at high rates of shear, there is much conflict in the experimental evidence relating to the behaviour in this respect of ordinary lubricating oils. It was suggested by Grunberg and Nissan1 that at high rates of shear the viscosity of ordinarily ‘Newtonian’ liquids might become a function of the rate of shear. They developed an equation to account theoretically for this dependence, and calculated that for n-pentane at 30° C. the viscosity should fall sharply over a range of the rate of shear from about 108 to 1011 sec.−1.