114 NATURAL HISTORY. 



close body, as through water ; through a wall ; 

 through metal, as in hawks bells stopped, &c. the 

 hard or close body must be but thin and small ; for 

 else it deadeth and extinguished the sound utterly. 

 And therefore in the experiment of speaking in air 

 under water, the voice must not be very deep within 

 the water : for then the sound pierceth not. So if you 

 speak on the farther side of a close wall, if the wall 

 be very thick you shall not be heard ; and if there 

 were an hogshead empty, whereof the sides were 

 some two foot thick, and the bunghole stopped; I 

 conceive the resounding sound, by the communica 

 tion of the outward air with the air within, would 

 be little or none : but only you shall hear the noise 

 of the outward knock, as if the vessel were full. 



213. It is certain, that in the passage of sounds 

 through hard bodies the spirit or pneum itical part of 

 the body itself doth co-operate ; but much better 

 when the sides of that hard body are struck, than 

 when the percussion is only within, without touch 

 of the sides. Take therefore a hawk s bell, the holes 

 stopped up, and hang it by a thread within a bottle 

 glass, and stop the mouth of the glass very close 

 with wax ; and then shake the glass, and see whe 

 ther the bell give any sound at all, or how weak : 

 but note, that you must instead of the thread take 

 a wire ; or else let the glass have a great belly ; lest 

 when you shake the bell, it dash upon the sides of 

 the glass. 



2 14-. It is plain, that a very long and downright 

 arch for the sound to pass, will extinguish the sound 



