108 Scientific Proceedings, Royal Dublin Society. 



flow as shown by height of water in current gauge, both increased 

 steadily till — 



2nd. The column of water in the tube ruptured at the constric- 

 tion, a roaring or hissing sound was produced, and the water just 

 below the point of minimum cross-section appeared milky with 

 small bubbles. 



3rd. At the moment of rupture or commencement of discon- 

 tinuous motion the pressure-difference, as shown by the mano- 

 meters, sharply increased, while the current diminished. 



4th. The pressure-difference at which rupture occurred was 

 not definite. Rupture was liable to occur if the pressure- difference 

 was above a certain fixed minimum, and the higher the pressure- 

 difference rose above this minimum the greater the liability to 

 rupture. 



5th. On closing the tap gradually current and pressure- 

 difference diminished, till at a certain definite pressure-difference 

 the water column united at the constriction and the hissing sound 

 ceased. 



6th. Eupture occurred more readily {i.e. at lower pressure- 

 differences) shortly after the apparatus had been connected to the 

 tap than after the water had been running for some time. 



7th. In an experiment in which the apparatus was connected 

 to the tap through a length of new grey rubber tubing, rupture 

 of the column occurred at a definite pressure, which did not 

 noticeably exceed the pressure at which the column would mend. 



The following is one series of observations : — 



Temperature of Air, . . 14-0° C. 



Temperature of Water, . . 10-8° C. 

 Barometric height, . . . 29-74 in. 



