Soap Bubbles
and the Forces which Mould Them

1^6 SOAP-BUBBLES, AND of the wax will make further electrification very uncertain. In showing the difference between an inner and an outer bubble, the same re- marks with regard to undue pressure, electrifi- cation, or loss of time apply. I have generally found that it is advisable in this experiment not to drain the drops from both the bubbles, as their weight seems to steady them; the external bubble may be drained, and if it is not too large, the process of electrically join- ing the outer bubbles, without injury to the inner one, may be repeated many times. I once caused eight or nine single bubbles to unite with the outer one of a pair in succes- sion before it became too unwieldy for more accessions to be possible. It would be going outside my subject to say anything about the management of lanterns. I may, however, state that while the experiments with the small bubbles are best projected with a lens upon the screen, the larger bubbles described in the last lecture can only be projected by their shadows. For this purpose the condensing lens is removed, and