Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. l6l ating experiments, and it is well worth while to make an effort to succeed. The little motor that I used is one of Cuttriss and Co.’s P. i. motors, which are very convenient for experiments of this kind. It was driven by four Grove’s cells. These make it rotate too fast, but the speed can be reduced by moving the brushes slightly towards the position used for reversing the motor, until the speed is almost exactly right. It is best to arrange that it goes only just too fast, then the speed can be perfectly regulated by a very light pres- sure of the finger on the end of the axle. Mr. Chichester Bell’s Singing Heater-jet. For these experiments a very fine hole about one seventy-fifth o£ an inch in diameter is most suitable. » To obtain this, Mr. Bell holds the end of a quill-glass tube in a blow- pipe flame, and constantly turns it round and round until the end is almost entirely closed up. He then suddenly and forcibly blows into the pipe. Out of several nozzles made in this way, some are sure to do well. Lord Rayleigh makes nozzles generally by cementing to the L