Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. 3^ dipping in and taking out a cork, which will cause the level to slowly change. So far I have given you no idea what force is exerted by this elastic skin of water. Measure- ments made with narrow tubes, with drops, and in other ways, all show that it is almost exactly equal to the weight of three and a quarter grains to the inch. We have, more- over, not yet seen whether other liquids act in the same way, and if so whether in other cases the strength of the elastic skin is the same. You now see a second tube identical with that from which drops of water were formed, but in this case the liquid is alcohol. Now that drops are forming, you see at once that while alcohol makes drops which have a definite size and shape when they fall away, the alcohol drops are not by any means so large as the drops of water which are falling by their side. Two possible reasons might be given to ex- plain this. Either alcohol is a heavier liquid than water, which would account for the smaller drop if the skin in each liquid had the same strength, or else if alcohol is not heavier than water its skin must be weaker than the skin of water. As a matter of fact alcohol is a lighter