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THE POPULAR SCIENCE MONTHLY. 



assume the form of Fig. 2. The twelve films from the edges of 

 the cube meet a square unsupported plate of film in the center. 



With No. 2 still on the frame, dip it again into the suds. You 

 catch a bubble by doing this which goes at once to the center 

 (Fig. 3), and forms such a cube as existed at the center of Fig. 1, 



Fig. 1. 



Pig. 2. 



Fig. 3. 



only large enough to show the curvature of the films necessary to 

 make them meet at their fixed angle. The laws of films formu- 

 lated are as follows : 1. From each wire edge of a frame proceeds 

 a film. Generally, if care be taken, no air will be inclosed, then 

 every film will be in contact with the surrounding air on both its 

 faces. 2. Only three films can meet at any liquid edge. 3. When 

 several liquid edges terminate in one point in the interior of the 

 system, the edges are always four in number, and the angles in- 

 cluded between them are equal. 4. Whenever the films can fulfill 

 these conditions, and remain plain films, they are so ; when they 

 can not, they are curved, but so curved that their mean curvature 

 is null that is, if in one part of the film the law of its union re- 

 quires an upward curvature, in some other portion there will be 

 an equal downward curvature to compensate for it. 



In the films upon the cube frame, for in- 

 stance, there is a slight curvature, just enough 

 to enable them to meet each other on the an- 

 gle of 120. This is a very simple digression 

 from the plane form, but in many other frames 

 the divergence is very marked ; for instance, 

 in the triangular pyramid (Fig. 4) with wires 

 dividing each side, after a bubble has been 

 entrapped by a second dip, the curvature is 

 very remarkable. 



Plateau, the blind philosopher of Ghent, 

 first studied this subject and formulated these laws. He began his 

 studies with some experiments far removed from our films. In 

 order to get some idea of the interaction of the molecular forces, he 

 removed a mass of liquid matter he was observing, as far as he 

 could, from the action of the physical forces. Using the well-known 

 principle that a submerged body sinks till it has displaced its 

 own weight of the fluid in which it is immersed, he made a mixt- 



Fig. 4. 



