These experiments consisted of the measurement of the moment transmitted, by fluid viscosity, across the annular space between two concentric cylinders, one of which revolves while the other is stationary. The fluid used in these experiments was water. Three distinct sets of conditions were tried, viz. :- (1) Outer cylinder revolving, inner cylinder stationary. (2) Inner cylinder revolving, outer cylinder stationary. (3) Repetition of series (1) with an annulus of different width.