Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. 43 take the same quantity of water and lay it carefully upon a cake of paraffin wax dusted over with lycopodium which it does not wet, what will happen ? Here again the weight of the drop—that which makes it fall if not held —will squeeze it against the paraffin and make it spread out into a flat cake. What would happen if the weight of the drop or the force pulling it downwards could be prevented from acting ? In such a case the drop would only feel the effect of the elastic skin, which would try to pull it into such a form as to make the surface as small as possible. It would in fact rapidly become a perfectly round ball, because in no other way can so small a sur- face be obtained. If, instead of taking so much water, we were to take a drop about as large as a pin’s head, then the weight which tends to squeeze it out or make it fall would be far less, while the skin would be just as strong, and would in reality have a greater moulding power, though why I cannot now explain. We should therefore expect that by taking a sufficiently small quantity of water the mould- ing power of the skin would ultimately be able almost entirely to counteract the weight of the