v THE SENSE OF BEAEING 223 



irregular periodic movements of elastic bodies, is routined within 

 certain limits of intensity and pitch. 



Many physicists and physiologists have attempted to ti\ the 

 lon-er I tin if, of auditory capacity that is, the minimum of pcndular 

 oscillations per second necessary to produce an acoustic sensation. 

 Sauveur (1700) was the first who determined the lowest audible 

 sound with organ pipes, and estimated it at 12i vibrations per 

 second. Cladni (1802) and Biot (1829), who used strings, gave 

 the limit as 16 vibrations. Helmholt/ found the note of a tuning- 

 fork audible that gave 26 vibrations per second. Wolf (1871) 

 made the same observation. Preyer (1876) used metal tongues 

 that gave 8 to 40 vibrations, and found that in some particularly 

 sensitive persons the minimal limit was 16 vibrations, in other 

 normal individuals 33. Appunn (1887-88) with his lamella 

 estimated the limit at 9-12 vibrations; Cuperus (1893) with the 

 same method at 10-13; van Schaik (1893) and Battelli (1897) at 

 24; Gradenigoat 8-12. 



In all these researches there is an error of method, since the 

 possibility that the ear perceives harmonic partial tones is over- 

 looked. Eecent experiments in fact show that none of the different 

 sources of sound employed are capable of producing single tones 

 entirely free from partials. Not only strings, but also metal tongues, 

 organ-pipes, and even tuning-forks produce tones mingled with 

 harmonic overtones, as may be shown by suitable resonators. 

 Helinholtz recognised that a tuning-fork vibrating strongly at 

 64 vibrations per sec. gave as many as five partials. To exclude 

 these, Preyer attempted to reinforce the fundamental tone with 

 resonators; but even by this means he failed to separate it from 

 the overtones. In fact resonators to some extent strengthen the 

 partial as well as the fundamental tones. In order to produce 

 a very low tone, free from harmonic partials, Helinholtz loaded 

 the strings with metal weights, so that on sounding they gave 

 only dissonant partial tones which could not blend with the 

 fundamental tone; but with this method the fundamental tone 

 became too weak for the purposes of the experiment. 



Accordingly it is not possible to assign any tone of given 

 pitch as the lower limit of audition. Individual differences in 

 the capacity for perceiving tones can be detected even within 

 normal limits of hearing, and the lower threshold of auditory 

 capacity alters considerably with practice and with the degree of 

 attention given by the subject. 



Below 40 vibrations per sec. tones lose their musical character 

 and become gradually weaker, indistinct and discontinuous. 



Experimental data to determine tin- ////"/ limit, of auditory 

 capacity were given by the same authors who endeavoured to 

 establish the lower limit. The earliest (Sauveur, Cladni, P.iot, 

 and Wollaston) range from 6400 to 200,000 per sec., but are entirely 



