2 NATURE OF THE GRAVE HARMONICS. 



dies, the discrimination of pcrfons, which is the office of the 



eye, and thofe modifications of lime; called fymphony and 



harmony, which are judged of by the ear. 



The ear affords Each fenfe reckons time, by the train of its own ideas alone ; 



f p \^ n a c n c ^ onof tlie auditory organ on this account meafures the lapfe of it by 



found, only found. Now if the ear had (he power of confidering the 



when the vibra- f ma ]j e ft intervals of time apart, it would perceive the conftitu- 

 tions are too fre- ; * ' » , 



quent to be fe- ent vibrations of founds as feparate dillind things, attracting its 

 parately confi- notice fuccefiively ; in which cafe, the human mind could not 

 pollibly form a conception of a permanent found : but it is a 

 maxim in harmonics, that a certain number of vibrations in a 

 fecond is required to give a fenfible degree of duration to the 

 note of a firing ; I fliall at prefent make ufe of 12 for this num- 

 ber. The preceding fact afcertains an eflTential point of my 

 theory, for it fixes the leaft interval of time that the ear can 

 but the ratios of con tern plate apart; this organ therefore takes in the grofs all 

 '"cefved ^nd ma g mtlu l es °f this defcription, which are too fmall to be exa- 

 excite ideas of mined in detail : in this cafe it acquires the ideas of acute and 

 acute and grave, grave, by comparing two or more trains of vibrations ; the in- 

 tervals of which are equal in each feries taken feparately, but 

 greater and lefs in the whole number taken together. 

 Two continuous When two founds, thus conftituted, are heard in concert, 

 founds,^ heard ^ v i Dra tions producing them are arranged in cycles, no one 

 their vibrations of which continues for a longer or fhorter time than the reft ; 

 arranged in and their effe6t is perceived by the ear, which becomes fen- 

 duration percep- lible of their prefence. For when each cycle of a feries, fepa- 

 tibleby the ear : ra tely confidered, exceeds the twelfth part of a fecond, the 

 be long enough, tenfc of hearing recognizes each point of divifion made by the 

 <ych cycle is dif- coincidence of the vibrations which feparate the contiguous 

 tinguifliedj C y C l es: this circumftance enables the fenie to contemplate 

 if not, the points thefe periods apart, and to comprehend their origin. On the 

 of recurrence contrary, when the duration of a cycle belonging to a corn- 

 will have the , ,- . , 11 in i r r j ^i 

 eft'eft of fimpie pound iencs does not exceed the twelfth part of a lecond, the 



periods, interval proves too fmall to be meafured by the ear; it there- 



fore efcapes notice in a feparate ftate ; for the points of divi- 

 fion recur too frequently to be obferved. When the auditory 

 organ finds itfelf in circumftances anfwering to the preceding 

 defcription, it has but one method to purfue ; which is to treat 

 thefe derivative intervals in the fame manner it treats all pe- 



ana afford a mu-riods which are fingly too fmall for its comprehenfion : it 



fkal found, or therefore reduces them to a iimple mufical found, correfpond- 

 grave harmonic, . 



