Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. 123 out by the elasticity of the bubble, catches fire and burns with a flame five or six inches long (Fig. 53). You might also have noticed that when the bubble was removed, the vapour inside it began to pass out again and fell away in a heavy stream, but this you could only see by looking at the shadow upon the screen. You may have noticed when I made the drops of oil in the mixture of alcohol and water, that when they were brought together they did not at once unite ; they pressed against one another and pushed each other away if allowed, just as the water-drops did in the fountain of which I showed you a photograph. You also may have noticed that the drops of water in the paraffin mixture bounced against one another, or if filled with the paraffin, formed bubbles in which often other small drops, both of water and paraffin, remained floating. In all these cases there was a thin film of something between the drops which they were unable to squeeze out, namely, water, paraffin, or air, as the case might be. Will two soap- bubbles also when knocked together be unable to squeeze out the air between them ? This