"The morning is come unto thee, O thou that dwellest in the land: the time is come, the day of trouble is near, and not the sounding again of the mountains."—Ezekiel vii.
738. Why may the scratching of a pin at one extremity of a long pole be heard by applying the ear to the opposite extremity?
Because wood is a good conductor of sound, and its atoms are susceptible of considerable vibration. It is, therefore, chosen in numerous instances for the construction of musical instruments.
Deaf persons have been known to derive pleasure from music by placing their hands upon the wood-work of musical instruments while being played upon.
739. Why is the hearing of deaf persons assisted by ear-trumpets?
Because ear-trumpets collect the vibrations of the air into a focus, and make the sounds produced thereby more intense.
740. Why are sounding-hoards used to improve the hearing of congregations?
Because, being suspended over, and a little behind, the speaker, they collect the vibrations of the air, and reflect them towards the congregation.