of a Liquid Mass without Weight. 43 



swell ; and since the viscosity of the liquid will at the same time 

 greatly retard the descent of the molecules towards the lowest 

 point of the curvature, the film will go on bulging and swelling ; 

 and, lastly, inasmuch as it is supported by a circular periphery 

 and is continuous throughout its whole extent, starting from this 

 periphery, it must, in accordance with a principle established in 

 my Fourth Series, constitute a portion of a sphere. As we 

 continue to blow into the bubble, the portion of a sphere thus 

 formed must evidently increase continually in diameter until the 

 film becomes at last so thin that it breaks. 



If we stop blowing before getting near the point at which the 

 bubble would burst, and give the pipe a rather rapid upward 

 movement, the bubble lags behind to a greater or less extent, on 

 account of its inertia and the resistance of the air ; but in con- 

 sequence of its cohesion and its adherence to the solid edge, the 

 film in most cases does not break, and the bubble remains for an 

 instant united to the edge by a hollow stem formed by an up- 

 ward extension of the film. Now if, for greater simplicity, we 

 suppose the rapid motion of the pipe to take place in a direc- 

 tion exactly perpendicular to the plane of the opening, the form 

 of the film must still constitute a figure of revolution ; and I 

 have shown in my Fourth Series that the sphere is the only 

 equilibrated figure of revolution closed upon the axis; this 

 stemmed figure therefore cannot, since it is closed below upon 

 the axis, constitute a figure of equilibrium ; consequently it must 

 undergo a spontaneous modification ; and it is evident that the 

 hollow stem will contract so as to separate into two portions, of 

 which the upper one will go to fill the mouth of the pipe as a 

 plane film, while the lower one will close the bubble, which thus 

 becomes isolated in the air and forms a complete sphere. 



Everybody knows that it is possible to blow bubbles in this 

 way at the end of a narrow tube that is not widened out. In 

 this case, when the end of the tube has been plunged into the 

 liquid and withdrawn again, capillary action retains a short column 

 of liquid in the tube, and on afterwards blowing in at the other 

 end, this column comes to form a small liquid mass over the 

 open end, and the air entering into it expands it and converts it 

 into a bubble. 



I next recall a well-known but curious process for the pro- 

 duction of plane, or nearly plane, films of liquid. A bottle con- 

 taining a small quantity of the glycerine- solution is taken in 

 both hands, by the neck and by the bottom, and, being held 

 horizontally, a movement is given to it which obliges the liquid 

 to sweep over the whole internal concave surface. As soon as 

 the motion is stopped, one or more plane films are found to be 

 arranged across the bottle, which can then be set upright on a 



