77 
of Edinburgh, Session 1866 - 67 . 
the normal polyhedron a few millimetres in the soap solution, the 
film formed on its lower face imprisoned the air in the quadran- 
gular pyramid above it, and that this air rose to the centre of the 
cube, and replaced the quadrangular plane with a hollow cube with 
curved faces. 
In this beautiful experiment the hollow cube is invariable in 
size, being necessarily equal in its contents to one-fourth part of 
the wire cube. The author of the present paper discovered a 
method of inserting a hollow cube of any magnitude in the centre 
of the polyhedron. This was done by blowing a bubble of the re- 
quisite size, and introducing it within the wire cube. He suc- 
ceeded also by this means in inserting a second hollow cube beside 
the first, the side common to both being plane when the two cubes 
were equal, convex when the one was less, and concave when it was 
greater than the other. In such a system, which is in perfect 
equilibrium, the number of films is nineteen. He found also that 
two hollow solid figures could, by the same means, be inserted in 
the other systems of films which Professor Plateau had discovered 
in a wire tetrahedron, or a quadrangular pyramid, or a regular octo- 
hedron, or a rectangular prism, or in a system obtained from two 
rectangular planes fixed at right angles to each other. 
This last and interesting system consists of four curved films 
extending from each vertical wire, and connected with an elliptical 
film in the common section of the rectangles. The major axis of 
this film is four times greater than its minor axis, and it is placed 
in the angle, which is a little greater than 90°, but sometimes 
also in the other angle. 
By making this system of wires movable, so that the rectan- 
gular planes can pass from 90° to 180°, the author obtained some 
singular results. As the angle increased from 90°, the minor axis 
of the elliptical film increased, till when it approached to 180° it 
was nearly circular, appropriating gradually the fluid of the four 
curved films attached to the wires. 
By again diminishing this angle the almost circular film became 
more and more elliptical, till it reached its normal state at 90°, 
giving back to the curved films the fluid which formed them. If 
the angle of the rectangular plane which contain the elliptical 
film is diminished, the film will grow more elliptical, and at 45° 
