56 UNIVERSITY OF MISSOURI STUDIES 



hear a tone and during one-tenth of the period we should 

 hear nothing so far as the nerve ends of this section are con- 

 cerned. The pitch of the tone we must expect to lie between 

 the tones 34 and 25, acording to the probable frequency with 

 which the stimulations are received during that part of the period 

 during which they are received. 



It is plain that the fourth, fifth and following sections of the 

 partition must move up and down very much the same as the third 

 section does, with this difference only, 

 The "mean" tone that for each further section the pause 

 when no stimulations at all are received 

 becomes longer and longer. The total sensation, then, which 

 is derived from the sum of the nerve ends of the third and the 

 following sections must be a tone of a certain intensity at a 

 certain time when all these sections mediate the sensation, 

 but becoming weaker and weaker as one after another of the 

 sections stops moving until for a moment it ceases alto- 

 gether, then appearing again and increasing up to its former 

 intensity. And so on again and again. That is to say, we 

 hear this tone "beating." And since its pitch lies probably 

 somewhere between 2(4 and 2'5i, between the "primary" 

 tones (perhaps its pitch is not quite constant but may 

 vary slightly during each period), I propose to call it 

 the "mean tone" (German: Zwischenton). The question 

 whether we hear such a mean tone I do not care to answer 

 here, this discussion being devoted to theory, not to experi- 

 mental research. Let the reader who desires make observa- 

 tions of this kind himself. 



The farthest section of the partition set in motion by this 

 movement of the stirrup moves up and down only once dur- 

 ing the period. The nerve ends located 

 The difference here receive one shock during each period 



tone and convey therefore the sensation of the 



tone 1, the difference tone of this case. The 

 intensity of the difference tone, corresponding to the length 

 of this section of the partition, is two. 



