EVAPORATION ON THE MOTION OF THE FLUIDS 65 



Fr'g-.lO 



permeable for the particles of air than a slice of 

 horn of the same thickness. 



If we introduce water 

 into the tube in the po- 

 sition Fig. 10, to the line 

 marked b, and, after fill- 

 ing the narrow part of 

 the tube with mercury, 

 invert it in a vessel of 

 mercury, Fig. 11, we ob- 

 serve a number of minute 







bubbles of air passing 

 through the moist blad- 

 der into the tube. The 

 mercury falls to a certain 

 point, which is higher or lower according to the 

 thickness of the bladder ; it stands at a lower level 

 with a thin membrane than with a thick one. When 

 a single layer of ox-bladder is used, it falls to 12 

 inches (above the level of the mercury in the ves- 

 sel) ; with a double layer it stands at from 22 to 24 

 inches. 



If we take care to allow the water standing above 

 the mercury to enter the wide part of the tube, so 

 that the bladder is kept at all times covered with 

 water, the mercury remains stationary at the same 

 level. If, for example, it stood at 12 inches, it 

 remains there, although the quantity of water is 

 constantly diminishing by evaporation from the 



F 



Experi- 

 ents. 



