The motion of a mercury index in a capillary tube

The general case of the motion of an index of any liquid is considered theoretically and it is shown that the viscosity of the liquid can be determined by observation of the velocity of the index when different pressure-differences are applied between its ends. Experiments on the motion of mercury indexes are described; they lead to a value of the viscosity which is about 6 per cent higher than the accepted value. The discrepancy is attributed to the electrification of the walls of the tube which continues to increase slowly even after the index has made several excursions along it. It is found that the difference between the angles of contact at the two ends is practically independent of the velocity of the index.