PAPERS PRESENTED AT GENERAL SESSIONS 



39 



striiments tested may be classified as ^' Sound Collect- 

 ors", "Sound traps'', speaking tnbes, and telephones. 

 Under the first group may be included all the modifica- 

 tions of the simple conical horn. The observations were 

 made by a deaf observer, Mrs. M. H. Liddell, of Lafay- 

 ette, Ind., whose skillful aid it is a pleasure to acknow- 

 ledge. They consisted in timing the duration of audible 

 sound, with the instrument held to the ear, and without. 

 From the ditference of these times, the amplification of 

 sound is computed as in the case of reduction by parti- 



Fi&ure 9. 

 Reduction of Intensity of Sound of dif- 

 ferent pitches transmitted by Hair 

 Felt, plotted as a function of the 

 thickness. 



tions. The results showed that the order of amplifica- 

 tions produced followed that of the relative sizes of the 

 instruments. The largest one tried produced a magnifi- 

 cation of some twenty fold. It is of interest to note that 

 simply holding the hand to the ear was as effective an aid 

 as any but the largest of the ear trumpets. The instru- 

 ments which I have denoted as sound traps are modifi- 

 cations of the open horn, obviously designed to secure 

 magnification of sound intensity by reflection and focus- 

 ing of the sound by curved surfaces. That such effects 



