THEORY OF COMPOUND SOUNDS. 153 



one of the conflituent founds be not equal to the fame intervals The intervals of 

 , , , r . r , i • i -l xu r the pulfes are not 



belonging to the found or iounds which accompany it, the le- equal) but in _ 



condary intervals, or fmall parts of time feparating the pulfes creafe anddimi- 

 which fall in fucceffion on the ear, will vary in magnitude; 111 perl ° ica y * 

 in the fame manner that the diflances between the figures upon as in a fcale an <* 

 the face of a barometer and its nonius vary, none on the Aider 

 coinciding with thofe on the fixed plate excepting the higheft 

 and lowefl. I have chofen this familiar inflrument to illuftrate 

 Dr. Smith's method of explaining the phyfical caufe of com- 

 pound founds, becaufe it affords a viflble example of a cycle 

 of pulfes, according to his notion of the fubjecl. 



The lketch which I have exhibited of Dr. Smith's hypo- Another theory 

 thefis (hews, that he allowed that a number of fimple founds ( Dr * Youn S' s )» 

 might exifl in concert, and ftrike the ear in a diftinft manner, 

 without fuffering any interruption in their motions from the 

 interference of their pulfes. But a late writer on found re- 

 jects this axiom in Harmonics as a mathematical inconfiflency ; 

 and fubflitutes the following theory of compound founds in the 

 room of it. If two mufical firings, differing in their times of that the pulfes 

 vibration, happen to vibrate in concert, they do not occa£on coae ce * 

 two diflincl: founds in the opinion of this gentleman, becaufe 

 the firings agitate the air in conjunction ; confequently the 

 pulfes, which one of them would actually form in an undif- 

 turbed atmofphere, muft unavoidably clafh with thofe which 

 the other firing would produce in fimilar circumflances. 

 Hence the waves of air belonging to both firings are inter- 

 rupted in their natural progrefs, and are compelled by their 

 mutual interference to coalefce, thereby producing a new fuc-andformapecu- 

 ceffion of pulfes, conflicting a fingle found in the place of *> r [t s un ^ fe h s av " 

 two. This found is of a peculiar kind; for, the pulfes of unequal and dif- 

 which it confifls, are feparated by unequal intervals of time, P ofed in c 2 cles « 

 and difpofed in cycles. 



The merit of the preceding theory, when compared with Examination of 

 Dr. Smith's hypothefis, muft be afcertained by contrafling it the > tterth «>ry. 

 w T ith a variety of fads, which are furnifhed by the phenomena 

 of compound founds, and make a part of every man's expe- 

 rience. For, if it be found upon examination to be repugnant 

 to thefe facts, it will prove inconfiflent with nature, and cannot 

 fail of difappointing the inventor's expectations. 



Were it poffible for a number of founds to coalefce, and form If founds could 

 but one, the compound would acquire fenfibIepropertiespeculiar coa, ^" the y 



to new compound j 



