312 ILLINOIS STATE ACADEMY OF SCIENCE 



A SIMPLE DEVICE FOR THE ANALYSIS OF 

 SOUND WAVES 



C. J. Lapp, University of Illinois 



This sensitive device was designed while research 

 was being done on the wave form of the sound emitted 

 by C. T. Knipp's singing tube. The principle used is 

 similar to the one employed by D. C. Miller in his phono- 

 deik. The optical reflecting system, however, was en- 

 tirely different, being at the same time much simpler. 

 The diaphragm of dermatype paper was stretched over 

 a two inch circular opening in a brass plate, 0.159 cm. 

 in thickness, and held in place by a flat brass ring of 

 the same thickness screwed to the plate. To the center 

 of the diaphragm were attached perpendicularly four 

 or five silk fibers, the other end of which was held by a 

 very fine conical aperiodic spring. Across the dia- 

 phragm, 0.476 cm. above and parallel to it, was very 

 tightly stretched one strand of a three strand silk thread. 

 This was passed 0.154 cm. from the perpendicular fibers. 

 A small mirror, 0.0435 cm. in width and 0.154 cm. long, 

 was mounted with its plane parallel to the diaphragm 

 between the horizontal silk strand and the vertical silk 

 fibers. When a sound wave was caught by the dia- 

 phragm the mirror vibrated with it around the horizon- 

 tal silk strand, causing a beam of light to vibrate and 

 trace out the sound wave form on a moving photographic 

 plate. 



F. A. Schultze* has shown that paper is aperiodic and 

 that a paper diaphragm is sensitive to sounds of any 

 wave length. The dermatype paper used was taken from 

 dermatype stencils manufactured for the Edison-Dick 

 mimeograph. This paper is flexible, and very strong. 



In the diaphragm mounting the author has incorpor- 

 ated some new features which are shown in Figs. 1 and 2. 

 No horn or resonating device of any sort was used in 

 any of the work to increase the intensity of the sound 

 brought to the diaphragm. Professor Foley, of Indi- 

 ana University, read a paper before the St. Louis meet- 



♦ Annalden d. Physik IV, Folge, Vol. 24. p. 75, 1907. 



