Soap Bubbles
and the Forces which Mould Them

^4 SOAP-BUBBLÉS, ANO vessel, which is not quite full. The bead always goes to the side of the vessel. It is impossible to make it remain in the middle, it always gets to one side or the other directly. I shall now gradually add water until the level of the water is rather higher than that of the edge of the vessel. The surface is then rounded near the vessel, while it is hollow near the bead, and now the bead sails away towards the centre, and can by no possibility be made to stop near either side. With a paraffined bead the reverse is the case, as you would expect. Instead of a paraffined bead you may use a common needle, which you will find will float on water in a tumbler, if placed upon it very gently. If the tumbler is not quite full the needle will always go away from the edge, but if rather over-filled it will work up to one side, and then possibly roll over the edge; any bubbles, on the other hand, which were adhering to the glass before will, the instant that the water is above the edge of the glass, shoot away from the edge in the most sudden and surprising manner. This sudden change can be most easily seen by nearly filling the glass with water, and then gradually