Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. 149 Thaumatrope for showing the Formation and Oscillations of Drops. The experiment showing the formation of water-drops can be very perfectly imitated, and the movements actually made visible, with- out any necessity for using liquids at all, by simply converting Fig. 35 (at end of book) into the old-fashioned instrument called a thauma- trope. What will then be seen is a true repre- sentation, because the forms in the figure are copies of a series of photographs taken from the moving drops at the rate of forty-three photographs in two seconds.1 Obtain a piece of good cardboard as large as the figure, and having brushed it all over on one side with thin paste, lay the figure upon it, and press it down evenly. Place it upon a table, and cover it with a few thick- nesses of blotting-paper, and lay over all a flat piece of board large enough to cover it. Weights sufficient to keep it all flat may be added. This must be left all night at least, until the card is quite dry, or else it will curl 1 For particulars see Philosophical Magazine, Sep- tember 1890,