I9II.] 



THROUGH A PARTITION OF WATER. 



119 



deducted), /3„,, puu pg, the densities of mercury (o° C), water {t° C), 

 and glass, respectively, m the mass of the imprisoned air at v, R its 

 gas constant, and T = t-\-2y2>° its absolute temperature. M is the 

 mass of the glass of the swimmer and g the acceleration of gravity. 

 The equilibrium position of the swimmer is unstable. To find it, 

 R may be raised and lowered for a fixed level of the swimmer; or R 

 may be clamped and the proper level of the swimmer determined hy 

 suction and release at C. The dropping of the swimmer throughout 



n 



A 



^ 



~d: 



--.[ 



r 



Fig. 2. Cylindrical Swimmer. 



the column of water may occasion adiabatic change of temperature 

 of .23°. It was my practice to use the latter method and to indicate 

 the equilibrium position of the swimmer by an elastic steel ring, 

 encircling A. In this w^ay the correct level may be found to about 

 I mm., and afterwards read ofi^ on the cathetometer. 



After making the observations, the hose ab is to be separated at 

 a, so that the swimmer falls to a support some distance above the 

 bottom, admitting of free passage for diffusion. Clearly this dif- 

 fusion is due to the difference of level, h" , between the water level in 

 z' and at the free surface of the liquid, / (see Fig. 2). Increase of 

 barometric pressure has no differential effect. A large head h" how- 

 ever means a longer column for diffusion. 



5. Data. — In the following summary a few of the data made in 

 1900 are inserted, chosen at random. 



