1916] 



on Problems in Capillarity 



803 



the amount of the amplitude of the vibrations is seen to exceed 

 2 cm., in a ring of 3 cm. diameter. 



In another form of exhausted vessel, shown in Fig. 11, the 

 film is obtained on a rectangular glass frame. This frame was made 

 of glass rod • 2 mm. diam., and must be symmetrically placed in 

 the tube. To obtain the film the liquid has simply to be smoothly 

 decanted out of the bulb to the opposite end and carefully returned, 

 taking care that the frame emerges at right angles to the surface of 

 the retreating liquid. The shape of the bulb permits the film to be 



^^^ 



Fig. 11. 



set up for examination with either its long or short side vertical, 

 while retaining the liquid in the bulb. 



For the measurement of the rate of extension of the black the 

 wire ring or some similar supporting frame is very convenient, as 

 the film is thus completely contained and isolated from excess liquid. 

 The line of demarcation between the black and the remainder of the 

 film is very clearly marked, and with the proper illumination the fail 

 can easily be followed on a cathetometer. Different soap solutions 

 give different results, and temperature effects are very marked. The 

 next table includes some typical results obtained at ordinary tempera- 

 ture with solutions of potassium and sodium oleates approximating in 

 composition to that given by Plateau. 



3 G 2 



