Page:Popular Science Monthly Volume 36.djvu/648

 shapes cut in them to sustain the film. A very satisfactory one may be made with very little trouble and at slight cost: three feet of inch rubber tubing, a bell-glass, such as is used to shade night tapers, some pieces of cardboard or thin brass, which can be cut with the scissors, and an inch tin elbow, used in speaking-tubes and costing three cents. Fit the parts together as in Fig. 8. The diaphragms should be blackened and varnished if of cardboard; the holes in them can be triangular, square, round, or of any geometrical shape. A film is drawn across the hole in the diaphragm; it should be set upon edge till the colors are established, then it is to be laid across the mouth of the bell-glass, and into the other end of the tube notes can be sung; but the breath must not be inhaled or exhaled carelessly, or the film will be broken.

A closed mouth-piece may be made by filing off two tin toy trumpets two inches from the open end. Over one tie a stretched membrane of India-rubber sheeting, such as dentists use, or fasten



with paper a thin sheet of mica, E, or even tough, strong letter-paper may be used. Hold the second trumpet, F, reversed against this, and sing into it.

The colors and figures on these films, if one is patient and learns how to use the voice, are simply incredible they are so wonderful and gorgeous. Fig. 9, A, B, C, D, E, F, show the forms obtained on several diaphragms with the home-made phoneidoscope described above, some with the closed mouth-piece