•Z$Z On the Tones produced hy an Organ-pipe, Sec. 



piper, that with equal preffure they would be in the rati* 

 of the tones above mentioned. 



The prefent experiments are very different from thofe of 

 Prieftley and PeroUe on found in diiferent kinds of gafes. 

 The experiments of thefe two philofophers had relation only 

 to the intenfity with which the vibrations of another elaftic 

 body (of a bell ftruck by a hammer) are conduced through 

 thefe gafes. Perolle contradic^ls Prieftley's affertion, that 

 the power of conducing is as the denfities ; but to this rule 

 Prieftley himfelf makes an exception in regard to oxygen 

 gas, which appears to be a ftronger conduclor : azotic gas 

 was examined by neither of thefe philofophers. In hydro- 

 gen gas they both found the conducing power very weak, 

 which is no doubt owing to its little dcnfity, In oxygen 

 gas they found the found fomcwhat ftronger than in com-, 

 mon air; in the nitrous gas Perolle found it alfo fomewhat 

 ftronger. In carbonic acid gas Prieftley found the found 

 ftronger; but Perolle, weaker, duller, and foniewha% lower 

 than in common air: which laft circumftance I confider as 

 agreeable to truth, becaufe the vibrations of a founding body 

 muft be more retarded the denfer the furrounding fluid is, 

 or according to its greater preflure on that body. For this 

 reafon the vibrations of a body vibrating in onr atqiofpheric 

 air muft be a little flower than they would be in a vacuum; 

 as experience teaches that tl.e found of a bell becomes lower 

 the more it is tilled with water, or the deeper it is immerfed 

 in that fluid ; fo that, when it is ftruck at a confiderable 

 depth, it no longer emits a diftiutSl found, but rather a kin(J 

 of difcordaut ncif?. 



XI. Letter 



