AT THE BOUNDARY OF A LIQUID IN MOTION. 
561 
given volume of water through a glass tube, and then to deposit a coating of silver on 
the interior surface of the tube. If the time of flow was tlie same as before, allowing 
for the (usually very small) change in diameter, it would be conclusive evidence 
ao-ainst the existence of the effect. Such evidence I have most satisfactorily obtained. 
Since the experiments were to be merely comparative there was no object in 
attempting to keep the pressure constant throughout each observation, and the 
simplest apparatus could he used. The bulb tube AB was fixed in a large glass jar 
filled with water, and opening below into a wide tube T, also filled with water. The 
lower end of the bulb tube was attached to the capillary tube by an india-rubber joint, 
so that the ends of the two glass tubes should just meet. The top of the bulb tube 
could be put into connexion either with the air outside, or with an exhausted bottle 
which was used to fill the bulbs, as the apparatus was some distance from a pump. 
The temperature of the water in the glass jar and wide tube could he read off by a 
delicate thermometer. 
The time taken by the upper surface of the water to fall from A to B was observed 
by a stop watch. Before silvering the tube the whole apparatus was repeatedly 
taken to pieces and set up again, and the time of flow shown to be unaltered. 
The silvering solution was a modification of Liebig’s, and was made according to a 
mbcccxc.—A. 4 c 
