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Page:Popular Science Monthly Volume 35.djvu/618

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594
THE POPULAR SCIENCE MONTHLY.

mixture of soap and sugar with water. On withdrawing the frame its inner space will be occupied with a flat film. of so little weight that it does not visibly sag, but becomes more tense as it is attenuated. A closed contour of cotton or silk thread laid upon the film will lie in any form so long as the film is whole and its tension equal in every direction. But the instant it is broken

PSM V35 D618 Copper ring floating on water surface.jpg
Fig. 2.—Copper Ring floating on the Surface of Water.

within the contour the thread will stretch and assume a circular form as in Fig. 5, under the influence of the outward tensions of the rest of the film. It takes the shape in which it bounds as great a surface as its length permits, which is that of a circle. Prof. Schoentjes has varied upon this experiment by using, instead of a simple thread, a system composed of portions of rectilinear solids and portions of arbitrary form, made by passing threads loosely through pieces of fine straws (as in the object lying on the table in Fig. 5). This being placed upon the film and the film pierced, as in the previous experiment, invariably assumed a shape in which all the loose thread portions became arcs of a single circumference, of which the rectilinear solid portions (the straws) constituted chords—or the figure, according to Steiner, of the maximum surface that can be limited by a contour so composed, M. Terquem and M. Gossart, by breaking the film at one or more points outside of the contour, make the thread double into loops.

M. Gossart has studied the pressure of this supposed membrane surrounding the drop of water, and its variation under different degrees of curvature. Investigating its behavior in a