102 SOUND. [Lesson xvur. 



when stretched and properly struck : also a bell 

 and a glass, which are some of the fittest instru- 

 ments for musical modulations. Much more might 

 be said on the causes of sound in general j but for 

 a general notion, what has been already mention- 

 ed may suffice. 



To determine the nature and effect of different 

 bodies in conducting sound, Mr. George Sounder s 

 made a variety of experiments : some of his con- 

 clusions and remarks are as follow : 



Earth may be supposed to have a two-fold pro- 

 perty with respect to sound. Being very porous, 

 it absorbs sound, which is counteracted by its 

 property of conducting it, and occasions it to 

 pass on a plane, in an equal proportion to its 

 progress in air, unencumbered by any body. If a 

 sound be sufficiently intense to impress the earth 

 in its tremulous quality, it will be carried to a con- 

 siderable distance, as when the earth is struck with 

 any thing hard, as by horses' feet, or the motion of 

 a carriage. Plaister is proportionally better than 

 loose earth for conducting sound, as it is more 

 compact. 



Clothes of every kind, but particularly wool- 

 len ones, are very prejudicial to sound ; their 

 absorption of sound, may be compared to 

 their absorption of water, which they greedily 

 imbibe. 



A number of people seated before others (as in 

 the gallery of a chapel or theatre) considerably pre- 

 vent the voice reaching those behind ; and hencs 

 it is that we hear so much better in the front of the 



galleries, 





