6 3 o 



THE POPULAR SCIENCE MONTHLY. 



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 geo- 

 metrical 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 





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Fig. 9. Figures on Films in Phoneidoscope. 

 A, B, C, forms whirling and evanescent ; D, E, F, forms which remained for some time after the 



vibrations of film ceased. 



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 



