Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. IO9 intervals, which correspond with their move- ment, and so, as I explained in the case of the water-drops, the fork appears perfectly still. Now the speed is slightly altered, and, as I have explained, each new flash of light, coming- just too soon or just too late, shows the fork in a position which is just before or just behind that made visible by the previous flash. You thus see the fork slowly going through its evolutions, though of course in reality the legs are moving backwards and forwards 128 times a second. By looking at the fork or its shadow, you will therefore be able to tell whether the light is keeping exact time with the vibrations, and therefore with the water- drops. Now the water is running, and you see all the separate drops apparently stationary, strung like pearls or beads of silver upon an invisible wire (see Frontispiece). If I make the card turn ever so little more slowly, then all the drops will appear to slowly march onwards, and what is so beautiful,—but I am afraid few will see this,—each little drop may be seen to gradu- ally break off, pulling out a waist which becomes a little drop, and then when the main drop is