MR. A. MALLOCK ON EXPERIMENTS ON FLUID VISCOSITY. 
47 
indicate is a little more than *2 lb. per square foot at ten feet per second (practically 
the same as Mr. Froude’s and Professor Unwin’s). 
The exponent also of the velocity is not far from P8, but the velocities used in this 
series were so low that I should not attach much importance to the numerical deter¬ 
minations except as showing that the motion is really different in character from that 
which takes place when the inner cylinder is stationary and the outer one revolves. 
[Note added July 10th. 1895.—Since writing the above, I have, at Sir G. G. 
Stokes’ suggestion, added the set of experiments shown in Diagram 12. These 
experiments show that the moment transmitted is directly proportional to the depth 
of the fluid in the annulus measured from the lower edge of the suspended cylinder. 
They give therefore further and independent evidence that the mercury floor and 
short cylinder K do really supply boundary conditions such as must exist at any 
cross-section of an infinitely long annulus, if particles having the same radii on either 
side of the cross-section are to be without relative motion.] 
Table I. — Dimension and Constants of Apparatus. 
The letters refer to figs. (1), (2), and (3). 
Inches. 
Centims. 
Radius of Cylinder E 
. . . 3-915 
9-943 
E' . 
. . . 3*42 
8-687 
„ . „ A' . 
. . . 3-005 
7-632 
Height of cylinders . . 
, . . . io-o 
24-5 
Number of divisions on circle, 400. 
Tangential Force at Surface of Cylinder A required to turn it through one 
division of the circle. 
With torsion wire I. 
gram. 
•278 
•523 
gram. 
•0181 
•0338 
