378 On the Tones produced by an Organ-pipe 



height both in the infide and outfide; and the preffure fiif- 

 talned hy the bell was equal, therefore, to the prcflure of the 

 atmofphere. The pipe was blown by compreiring the blad- 

 der; but the greateft caution was neceffary to prevent the 

 pipe from emitting, inllcad of its natural tone, any of its 

 higher tones, which in an open pipe, as is well known, are 

 ?is the natural feries of the numbers, that is, in arithmetical 

 progreffion. A weak and uniform preflTure was therefore nc- 

 peffary, but which could be repeated at pleafure ; becaufe, 

 when the preflure was omitted, the fupevflnous gas returned 

 back into the bladder. The temperature, which certainly 

 contributes in fome degree to vary the tone of a wind inftru- 

 jiient, in regard to all the different kinds of gas, was always 

 the fame ; that is, the degree which is ufual on a fomewhat 

 cool morning in fpring, To enable me to judge with more 

 jiccuraoy of the tone, I had tuned two ftrings to an unifon of 

 that tone produced in common air : the experiments were 

 made with the utmoll accuracy, fo that I have reafon to 

 think there was no room left for the fmallefl: deception. 



The bell and the pipe being firfl: filled with common air, 

 the tone was exactly the fame as that of a pipe blown when 

 it is perfectly free ; but much v.eakcr, as mufl have been 

 expefted, becaufe the vibrations of the air inclofed in the 

 bell were propagated, and could be communicated to the 

 furrounding atmofphere only through the fides of the bell 

 and through the water. But though the found, for the fame 

 reafon, was fomewhat weak in the other experiments, they 

 pould, howe\er, be heard very difi:in6lly. 



In oxygen gas from manganefe the found was half a tone 

 or nearly a whole tone lower than in common air'. This nearly 

 agrees with th^ry ; according to which the difference mufl 

 a"mount to almofl half a tone, if the gravity of atmofpheric 

 air be to that of oxygen gas as i to 1*103, ^^^ the tone iu- 

 verfely as the fquare root of the gravity. 



The mofl Itriking deviation from theory was exhibited by 

 ^otic gas. ^t might have been expe^e4 that the found pf 



it 



