1916] on Problems in Capillarity 795 



on the side farthest from the doiihle bulb. The diameters of the 

 fihiis so obtained were varied in the different vessels nsed from 1 to 

 8 cm. After fining with the requisite amount of liquid, the Avhole 

 can be exhausted through the tubular extension of the reservoir. 

 In order to obtain a film the liquid is tilted over into one of the 



Fig. 6. 



double bulbs and swirled with a single gentle sweeping motion round 

 and over the neck, thus leaving a film across the opening. Witli a 

 suitably shaped neck, provided there is a sufficient amount of liquid, 

 very little practice is necessary. It may be added that fihns in the 

 double bulb of Fig. 6 remain indefinitely. Even without any neck, 

 a film can be obtained by practice in a plain cylindrical vessel of 

 considerable diameter. One such film 19 cm. in diam. in a closed 

 bottle is on the table, having become perfectly black since it was 

 thrown more than a week ago. 



The double bulbs have proved to be very convenient for system- 

 atic study of plane films, from the ease with which they can be 

 manipulated. In addition to the film at the neck, other fihns across 

 the tube as at C can be obtained. Such a film acts as a stopcock^ 

 isolating the opposite sides of the main film on the neck. This can 

 then be subjected to slight differences of pressure by gentle warmth 

 from the hand. Instead of a plane film varying degrees of curvature 

 can be obtained. Many effects on the character and appearance of 

 the films can thus l)e studied, and have proved interesting. 



The illumination, either for direct visual study or projection, is 

 easily arranged without much disturbance from the glass surfaces. 

 A slightly condensed beam of light from an arc lamp, passing through 



