AND FORMS OF LIQUID FILMS. 115 



plane film. The same result is produced, though no plane film is first formed 

 within the cone, by simply inserting two bubbles of equal size, so as to come in 

 contact with one another. In a similar manner, three bubbles may be inserted 

 in place of two, the result is the system shown in fig. 8, where the three bubbles 

 are united to one another by three plane films meeting in a central vertical 

 straight line. The system produced by inserting four bubbles in a similar 

 manner to the last, is a very curious and beautiful one, peculiarly interesting on 

 account of its analogy to the system already described in the previous paper, as 

 formed within the wire cube (vide " Transactions," vol. xxiv. p. 505). This system, 

 shown in fig. 9, consists of four similar figures, the curvatures of whose sides are 

 extremely curious, united in their centre, just as in the case of the system within 

 the wire cube, by a plane quadrilateral film bounded by convex lines. In the 

 case of the wire cube, it was seen that this plane film could be transposed from 

 the vertical to the horizontal position, by blowing upon its margin through a 

 small tube. It is difficult, if possible, to repeat the experiment in this form 

 upon the similar system within the cone, but the same result may be produced, 

 i.e. the system may be obtained with the plane film, in the horizontul position, 

 by means of the following process. 



It has been seen that in the case of the systems formed of two and three 

 bubbles respectively, it is immaterial whether we proceed by first obtaining a 

 plane film upon which the bubbles are inserted, or by simply inserting the bubbles 

 upon the sides of the cone without the previous existence of the plane film. But 

 in the case of the system now under consideration, if we proceed by first inserting 

 a plane film as a basis upon which to place the four bubbles, and take care that 

 these are not too large, the result is the system shown in fig. 10, in which it will 

 be seen the plane quadrilateral film connecting the four bubbles, instead of being 

 vertical, is horizontal, consisting in fact of the central portion of the original plane 

 film which has remained in situ, the remainder of it having amalgamated with 

 the films of the bubbles. A beautiful variety of this experiment may be made in 

 the following manner : — Having obtained the system with the plane film in the 

 horizontal position, withdraw the plug from MN, so as to allow the system to 

 rise in the cone (a result which can always be insured by gently sucking out the 

 air by the mouth from MN) ; the system being thus contracted, the sides of the 

 bubbles are brought in contact with one another, the horizontal film is first con- 

 tracted to a point, and then (the system being now unstable) passes into the 

 vertical position. By again blowing air in at MN, the system may be made again 

 to descend, and the plane film to pass once more into the horizontal position. 



It will be remembered that, in the case of the wire cube, a beautiful system 

 was produced by forming a small cubical film in the centre of the polyhedron 

 (vide " Transactions," vol. xxiv. Plate xxxiv. Fig. 4). This, it was seen, could 

 be produced either by dipping the cube a second time in the solution, or by blow- 



VOL. XXV. PART I. 2 G 



