131 
frame of a rectangular prism (figure 2). If this is dipped into a 
thick soap solution, and then removed, the direction of removal 
being parallel to the long axis of the frame (as indicated by the 
arrow in figure 2), there will be a quadrilateral face in the center 
which grows smaller and smaller; just as it vanishes a new face 
appears at right angles to the original one. This is easily demon- 
strable, the films slipping slowly, if the solution is dense enough. 
As known to Plateau and others, a soap solution to which glyc- 
erine has been added gives satisfactory results. 
l 
a 
i FIGURE 3, Photograph of an orthic tetrakaidecahedron, showing a square 
= bordered by four hexagonal faces. The four half-hexagonal faces of Figure 
are limited by the dotted lines. 
The orthic tetrakaidecahedron may be modelled in various 
Ways. Kelvin (1894) suggested soldering together thirty-six 
Pieces of wire. Figure 4 shows a layout for a paper model ; this, 
Printed on stiff paper, can be cut out, and folded on the heavy 
lines and glued by means of the flaps. It can be enlarged by 
means of the photostat. It is obvious that this is by no pera 
€ only arrangement possible for a paper model, but it is the 
most convenient. By using thin sheet meta 
and making the model in two parts, as indicated 
mold can be made; then by soldering the edges of each half of this 
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