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BELL SYSTEM TECHNICAL JOURNAL 



without the test stethoscope inserted in the sound path. In this 

 experiment, it was impracticable to set up pure vibrations in the 

 human body. \ piece of fresh beef was a convenient substitute and 

 one which for the purposes of such physical analysis appeared satis- 

 factory. 



The fre(iu(.n(\- characteristic of the open i)ill slclhoscope is shown 



Fig. 1 — The open bell stelhoseope 



1-ig. 2-(>n 



HmwIcs stethoscope 



in F"ig. H, in which the ".sen.sation value" as interpreted by the ear 



is plotted in transmission units,' TU, — convenient units ii>ed to 



'The transmission unit used in this paper is a logarithmic function of power 

 ratio. The number of transmission units N corresponding to the ratio of two 



p 

 amounts of power P\ and Pi is given by the relation A'=l() log,o— . The power 



N 



ratio corresponding to N units is therefore 10'». For example, an increase of 

 10 TV signifies 10 limes as nuich power: of 20 TV, 100 times as much power, etc. 

 See W. 11. Martin, "The Transmission I'nil," Journal A. /. E. E., Vol. 43, p. 

 504, 1924; B. 5. T. J. \ol. 3, p. 400, 1924. 



