SOUND. 327 



In the Cathedral church of Gloucester, there is a 

 whispering 'gallery above the eastern extremity of the 

 choir, which extends from one end of the church to the 

 other. If two persons, placed at the distance twentyfive 

 toises, speak to one another in the lowest voice, it is dis- 

 tinctly heard. A similar effect is produced in the vesti- 

 bule of the Observatory of Paris, and in the cupola of St 

 Paul's in London. Mr Southwell informs us, that, in 

 Italy, on the way to Naples, and two days' journey from 

 Rome, he saw in an inn, a square vault, where a whisper 

 could easily be heard at the opposite corner, but not at 

 all on the side corner that was near to you. This pro- 

 perty was common to each corner of the room. He saw 

 another on the way from Paris to Lyons, in the porch of 

 a common inn, which had a round vault. When any 

 person held his mouth to the side of the wall, several per- 

 sons could hear his whisper on the opposite side. 



The whispering gallery in St Paul's, London, is a 

 great curiosity. It is 1 40 yards in circumference. It 

 is just below the dome, which is 430 feet in chcum- 

 ference. A stone seat runs round the gallery along the 

 front of the wall. On the side directly opposite the door 

 by which visitors enter, several yards of the seat are 

 covered with matting, on which the visitor being seated, 

 the man who shows the gallery whispers with the mouth 

 near the wall, at the distance of 140 feet from the 

 visitor, who hears his words in a loud voice, seemingly at 

 his ear. The mere shutting of the door produces a 

 sound like a peal of thunder rolling among the moun- 

 tains. The effect is not so perfect if the visitor sits 

 down halfway between the door and matted seat, and 

 much less if he stands near the man who speaks, but on 

 the other side of the door. 



VI. MUSICAL SOUNDS. 



The smallesfnumber of vibrations which will produce 

 sound, is twelve and a half per second, and the greatest 

 number audible is 6400 per second. There are two 

 methods, both exceedingly ingenious and curious, by 

 which these numbers are ascertained, which however, 

 cannot here be explained. 



