Page:Popular Science Monthly Volume 20.djvu/192

180 tension of the whole contour. At length (Fig. 2, C 5) we find ourselves in the face of that curious form of mobile equilibrium of fluids of which we have noticed so many examples, and of which we have in a manner just studied the genesis and the anatomy. These singular wreaths have a still more singular constitution than we conceive; they are not full rings, nor even such simple hollow rings as we might make by bringing together the ends of an India-rubber tube. We have to

 closed by a membrane at its lower end, with a perforated disk in the middle, and half filled with tobacco-smoke; a push of the thumb on the membrane causes rings of smoke to issue through the orifice of the disk in the middle.

imagine a continuous necklace of watch-springs locked one to another along a circle, by which all their ends are joined; or, to speak geometrically, the figure of revolution which would be produced by a plane spiral turning round an asymptotic axis. Observation shows, together with a delicacy of design in the shaft, and a transparency which nothing can excel, fine horizontal striæ passing from one volute to another, and marking with exceeding neatness the number and divergence of the rollings. In water, effects of exquisite beauty may be produced directly without passing through the intermediate phases, by means of taps on the membrane of the apparatus. The experiment may again be simplified by forming with the membrane itself the bottom of the vessel, and using for an orifice a hole pierced in a disk which has been