566 
MR. W. C. D. WHETHAM ON THE ALLEGED SLIPPING 
V the velocity of the water calculated from the quantity which flows through in a 
given time. 
It was advantageous to use as small a tube as possible, for two reasons : firstly, 
because any slipping effect is inversely proportional to the radius, and secondly, 
because the gradient of velocity can be pushed farther without exceeding the limits 
of linear motion, the smaller the tube. 
A tube, whose diameter was '084 cm., and whose length was 27’30 cms., was 
therefore taken, as it was the smallest which could conveniently be silvered, and the 
greatest allowable pressure calculated. 
From the relation given above, we find that the pressure must not exceed 
dGQOixH/r^g = 303'5 cms. of water column. 
After many preliminary trials an apparatus was set up, which gave most excellent 
results. 
