>N BEATS OF IMPERFECT 

 HARMONIES 



\Heing Paper read before tJic Royal Society of Edinburgh, 

 April is/, 1878.] 



ACCORDING to a usage which has been adopted 

 from the German of Hclmholtz by the best English 

 scientific writers on sound, a sound is called a 

 " simple tone," 1 or without qualification a 

 " tone," when the variation of pressure of the 

 air in the neighbourhood of the car, which 

 is the immediate excitant of the sense, is accord- 

 ing to a simple harmonic function of the time ; 

 that is to say, when the deviation from the 

 mean pressure of the air varies in simple pro- 

 portion to the distance, from a fixed plane, of a 



1 The old musical usage, according to which the word tone 

 denotes an interval (the major tone or minor tone, or the mean 

 tone of the tempered scale), though it unfortunately clashes with 

 this recent scientific use of the word tone, can scarcely be 

 abandoned. 



