526 BELL SYSTEM TECIISICAL JOURS. -iL 



hie with undislorted speech having an intensity anywhere from one 

 hundred times greater, to a million times less than that at exit from 

 the mf)uth. On the whole the sounds, ///,/, s, and i' are hardest to hear 

 correctly and they account for over half the mistakes made in interpre- 

 tation. Failure to perceive them correctly is principally due to their 

 very weak energy although it is also to be noted thai the\- have im- 

 portant components of very high frequency. 



The Physical Criterion for Determining the Pitch of a Musical Tone.* 

 H.XRVKV FLETCHiiR. This paper describes experiments in which a 

 high quality telephone system was used to reproduce musical sounds 

 from the voice, the piano, the- \ inlin. the clarinet and the organ without 

 any appreciable distortion. Into tliis telephone system electrical 

 filters were introduced which made it possible to eliminate any desired 

 frequency range. Results with this system show that only the quality 

 and not the pitch of such musical sounds changes when a group of 

 either the low or high frequency components is eliminated. Even 

 when the fundamental and first se\cn oxertones were eliminated 

 from ilie xowel ah sung at an ordinary piuli for a baritone, the pitch 

 remained the same. These results were checked by a study of syn- 

 thesized musical tones produced by ten vacuum tube oscillators, with 

 frequencies from 100 to 1,000 at intervals of 100. It was found that 

 three consecutive component frequencies were sufficient to give a 

 clear musical tone of definite pitch corresponding td 10(1. .md that in 

 general when the adjacent components had a ri)ii>lant (liflcrence 

 which was a common factor to all coniiiomnls .i siiiLjlr nuisiial tone 

 of pitch equal to this common differenci' \\,i> oliiainrd. l)ul not otiu-r- 

 wise. Recent work on hearing has shown that the transmission 

 mechanism between the air and the inner ear has a non-linear response 

 which accounts for the so-called subjective tones. When the com- 

 ponents of low frecjuency are eliminated from the externalK' impressed 

 musical tone, they arc ai;ain iiiiroduicd as subjecti\e tones before 

 the sound r(.Mrhi> llu- nir\e lirniin,il>. ("alcuiation of the magni- 

 tude of these subjecti\e tones from ihc mm-linear constants of the ear 

 shows that the results on pitch ari- w h.ii might be expected. 



Sound spectra of ten typical musical sounds, obtained with an 

 electrical automatic harmonic analyzer to be describetl by Wegel and 

 Moore, are given for ah sung at pitch d, a sung at a, piano ri, piano c' , 

 \iolin i;', clarinet r, organ, pipe, Ci for three pressures, and oigan pipe c' . 



Ferromaiinetism and Its Dependence Upon Chemical, 'Thermal and 

 Mechanical Conditions.-' L. W. McKici^u.w. This review considers 



' Physical Review, Vol. XXIII, .No. ,?, March, 1924. 



■•Journal of Franklin histitute, V. 196, pp. 58.?-601; 757-786, 1924. 



