Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. out until at last it has the shape of a round straight tube or cylinder as it is called. We have spoken of the curvature of a ball or sphere; now what is the curvature of a cylinder ? Looked at sideways, the edge of the wooden cylinder upon the table appears straight, i. e. not curved at all; but looked at from above SIDE VIEW Fig- 24. it appears round, and is seen to have a definite curvature (Fig. 24). What then is the curva- ture of the surface of a cylinder? We have seen that the pressure in a bubble depends upon the curvature when they are spheres, and this is true whatever shape they have. If, then, we find what sized sphere will produce the same pressure upon the air inside that a cylinder does, then we shall know that the curvature of