Soap Bubbles
and the Forces which Mould Them

142 SOAP-BUBBLES, AND little heavier, and the liquid above ever so little lighter than oil, the drop of oil perhaps as large as a halfpenny will be almost per- fectly round. It will not appear round if seen through the glass, because the glass magnifies it sideways, but not up and down, as may be seen by holding a coin in the liquid just above it. To see the drop in its true shape the vessel must either be a globe, or one side must be made of flat glass. Spinning the oil so as to throw off a ring is not material, but if the reader can contrive to fix a disc about the size of a threepenny- piece upon a straight wire, and spin it round without shaking it, then he will see the ring break off, and either return if the rotation is quickly stopped, or else break up into three or four perfect little balls. The disc should be wetted with oil before being dipped into the mixture of spirit and water. A Good Mixture for Soap-Bubbles. Common yellow soap is far better than most of the fancy soaps, which generally con- tain a little soap and a lot of rubbish. Castille