2 Gibson, Bodies floating in a Free or a Forced Vortex. 



§ 2. Experiments on Free Vortex. The free vortex 

 experiments were carried out in a cylindrical tank, two 

 feet in diameter and one foot deep. This is supplied 

 with water through a pipe iMn. in diameter, making 

 connection with the tank through an external volute 

 whose centre line is six inches above the bottom of the 

 tank, while discharge takes place through a central hole 

 in the bottom of the tank. The intensity of the vortex 

 action was varied by enlarging this hole from one inch in 

 the first series of experiments to ijin. in the second series, 

 and by varying the head of water in the tank from 9 inches 

 to 12 inches. Throughout the experiments the motion 

 approximated very sensibly to that of flow in a true free 

 vortex. The motion, as investigated by colour bands, 

 was steady and non-sinuous, and the surface smooth and 

 free from waves. 



In the experiments carried out under a head of nine 

 inches, the form of the surface profile is indicated in the 

 following table. 



The first of these orifices discharges "0109 cub. ft. per 

 second, and the second 0152 cub. ft. per second under this 

 same head. 



A series of experiments carried out to determine the 

 value of the coefficient of discharge for each of the orifices 



