Experiments on Auditimi. W 



will be able to perceive the consonance or dissonance of the 

 two sounds ; the roughness of discords, and the beatings of im- 

 perfect consonances, are thereby rendered so extremely dis- 

 agreeable, and form so evident a contrast to the agreeable har- 

 mony and smoothness of two perfectly consonant sounds, that 

 it is impossible that they can be confounded, 



§3- 



Apply the broad sides of two sounding tuning-forks, both being 

 unisons, to the same ear ; on removing one fork to the opposite 

 dar, allowing the other to remain, the sensation will be consi- 

 derably augmented. 



It is well known, that when two consonant sounds are heard 

 together, a third sound results from the coincidences of their 

 vibrations ; and that this third sound, which is called the grave 

 harmonic, is always equal to unity, when the two primitive 

 sounds are represented by the lowest integral numbers. This 

 being premised, select two tuning-forks, the sounds of which 

 differ by. any consonant interval excepting the octave ; place the 

 broad sides of their branches, while in vibration, close to one 

 ear, in such a manner that they shall nearly touch at the acoustic 

 axis, the resulting grave harmonic will then be strongly audible, 

 combined with the two other sounds ; place afterwards one 

 fork to each ear, and the consonance will be heard much richer 

 rn volume, but no audible indications whatever of the third 

 sound will be perceived. 



§4. 

 Very acute sounds, such' as the chirping of the gryllus cam- 

 pestris, &c., are rendered inaudible by exhausting the air from 

 the Eustachian tube, and thereby producing a tension of the 

 membrane of the tympanum ; the different thicknesses or ten- 

 sions of this membrane may therefore occasion that diversity of 

 the limits of audibility, with regard to the acute sounds which 

 Dr. Wollaston has pointed out as existing in different indivi- 

 duals ; if so, it would be desirable to ascertain this limit in in- 

 dividuals in whom the tympanum is perforated, or destroyed. 



§5. 

 When the auricula is brought forward, all acute sounds are 

 rendered much more intense, but no sensible difference is per- 



