THE LAWS OF FILMS. 625 



easy to do, the form of the oval changes. At right angles the oval 

 film, is four times longer than it is broad. As the angle between 

 which the oval film stands is increased, it widens till it is nearly 

 square. If the rectangles could be made to lie exactly one upon 

 the other, the oval film would fill up the space. Now, when the 

 angle of the two wire frames is made narrower instead of wider, 

 the oval narrows till, at 45, it is a line, and in one moment the 

 system has changed : the oval stands between the wider angle just 

 across its old position and at right angles to it. 



A still more remarkable change takes place when a bubble is 

 blown upon the oval film, the lines being at right angles to each 

 other. When it reaches the proper size, all the films disappear, and 

 a hollow curvilinear cube is formed, each side curving out from 

 the wires which define its vertical edges. At the top and bottom the 

 wires make a cross on the film ; in each of these triangular spaces 

 four summits appear ; colored rings form around them ; a black 

 spot shows in the center of each summit, and the bubble bursts. 

 If the wires are held straight up and down when the bubble 

 bursts, the old system of films will start into being again, as if it 

 had left its ghost behind it to recover the elements which the 

 bubble had appropriated. 



Dr. Sloane, in his " Home Experiments in Science," gives 

 some beautiful figures. A wire is bent in a spiral, with one end 

 turned straight up through the middle like an axis. Dipped in 

 the fluid, it gives a single spiral film curving around the central 

 wire as a spiral staircase curves around its central pillar. He also 

 gives some very simple and interesting experiments showing the 

 traction of films, requiring no special apparatus or fluid, and so 

 within the reach of every one. All the frames used in this article 

 were made of thin copper wire bent into shape with the fingers 

 or a pair of pliers. Of course, if the wires are soldered instead of 

 being twisted together, and are covered with a thin film of par- 

 affin by rubbing a so-called wax candle on them and then holding 

 the frame above but not too near a bed of coals, the films will 

 last longer ; but that is the only difference. 



The wonderful traction of films is shown by the recent experi- 

 ments with oil upon the waves in a storm. The oil, of course, 

 does not still the waves, but it converts the combing waves, so 

 dangerous to navigators, into a comparatively harmless swell. It 

 is the traction of the film which prevents the wind from drawing 

 the water up the incline of the wave and sending it jetting up- 

 ward to fall over in a comb. A film of oil ^-oisVo-o of an inch in 

 thickness will hold the wave of water driving before a gale so 

 that it can not break into spray. 



The closing words in Brewster's experiment on the revolving 

 rectangles of wire bring us to another remarkable though famil- 



TOL. XXXVI. 40 



