24-1

Of Winds and Sounds.

to diffuse themselves in Form of Waves.Thus a Person speaking in one End of aTube, or Trumpet, will be heard as speak-ln g from the other. And as in the CafeLight, we fee the Image of an Objecta Ways in the Direction of the reflected^ a y; so in Echoes , we hear a Person speak^ the Place from whence the reflected*^ave comes to the Ear (CVI).

Because

1 7 - This was farther confirmed by the fame Gentle-. ^ by another Experiment he made afterwards, inj ^ch he found that an openPipe of about two/W/r Feet? Length, was in Unison with a String which vibrated0t ^ards and backwards 243 times in a Second ; where-fore i£Z^_ 4 | nearly: that is, the Length of a Pulseto 243 1

as about 4! Feet of Paris, or nearly twice the Length

of

the

Pipe

t ( , CVl ) >•

, _ In order to account for the Nature ofCf tOEs, we must consider, that Sound is perceived as

?fiug from that Place, from which, as a Centre, thef j ‘ es are propagated. This is well known by Expe-f s etlc e : But to illustrate this Matter, Igt A be the Centreftr4 "^ence an y Sound is directly propagated, andd f * es against any plain Obstacle C B, sufficiently large;so (V AF perpendicular to B C, and produce it to H,aat it may be A Far F H ; the Sound reflected willP e rceived as coming from the Point H.t hen*'° r * et AB be the incident Ray, impinging against^ j^^stacle B C in the Point E ; from E draw the Rayeqsj in such a manner that the Angle CED may be% a t0 ^ le Angle EF A, or that the Angle of Inci-tojj^^ a y be equal to the Angle of Reflection; thendn c D be the reflected Ray of Sound, and, if pro-spEi, will pass through the Point H ; for the Angle-^-CEDccFEA. Therefore in the Triangles

°I-. II.

R

AFE

Plateis. g

XXXII.Fi