Preparation for 

 experiment. 



152 EPFECT OF SOUND ON THE BAROMETER. 



founded on a ftrong vault, and totally independent of the wall 

 of the fteeple, might alone have anfwered the firft of thefe ob- 

 jections; but happily a moft complete and fatisfaclory anfwer 

 to both of them, was furnifhed by the manner in which the bell 

 was rung. 



As the bell was to ring out full in an inftant, at a fignal 

 given from below, it is neceflary to have it in motion fome 

 time beforehand; and during that time, the clapper is fixed to 

 one fide by a ftrong ftick croffing the mouth of the bell, which, 

 at the fignal, is pulled out by the hand of a perfon placed for 

 that purpofe. If then, our barometer fhewed no variation 

 during all this time, we were abfolutely certain that whatever 

 motion was perceived afterwards, was wholly owing to the 

 found. 



Mr. Pigott, who was then at BrufTels, was kind enough to 

 lend me one of his barometers, made by Ramfden, and his fon 

 made the following obfervations jointly withmyfelf ; 



At two o'clock in the afternoon of the lit of November 

 1773, we went into the north weft tower of St. Gudula's 

 church, and having fixed the barometer firmly in the opening 

 of a window, not above feven feet from the bottom of the bell, 

 we waited quietly for its ringing. 



The height of the mercury before the bell began to fwing, 

 as obferved by Mr. Pigott, was 29.478 inches. The bell be- 

 ing in full fwing, no alteration whatever was perceptible. 

 The inftant that the clapper was loofed the mercury leaped 

 was elevated by up an j continued that fort of fpringing motion, at every ftroke 



the found of a *\ , . . , , , . r, . • r i , „ 



krge bell. °* the clapper, during the whole time ot the ringing of the bell, 



Thefe were our obfervations : 



During the ringing of the bell, Mr. P. - 29.469 

 During the ringing, by myfelf. 



Higheft 29.480 



Loweft 29.474 



Higheft 29.482 



Loweft 29.472 



Narrative, 



The mercury 



Thefe obfervations were made with the greateft attention ; 

 and, confidering their delicacy and the difficulty of obferving, 

 agree very nearly. They appear to give from 6 to 10 thou- 

 fandths of an inch for the effect of this found on the barometer. 

 It is to be obferved, that Mr. Pigott, in general, cftimated 



the 



