IV

°f p r;t ,p Monopoly, while the remainder witness the ceremonyStance in dumb show.

tl," 8 ai 'e reflected by certain configurations of bodies,a P<;rs 6 '^ection of light from polished surfaces ; so that if''■ill j n ° n s * tuat ed before one of these bodies utter a word, he•oma a r s ^ort time after hear the echo, or repetition of thes °Kii(l' • ^‘ e vibratory motion of the air, which constitutesV fly’j ! s reflected by hard bodies, and, in certain cases, even®4rth tu' Thus the sides of a hill, houses, rocks, banks ofl^Vat 6 | lar § e t run ks of trees, the surface of water, espe-laVe h * 16 bottom °f a well, and sometimes even the clouds,SUfati een found capable of reflecting sounds. The confi-J'^d :-° f . the surface of these bodies, is much more con

on*

8,11 oo'q the production of the echo than their substance.

^ - surface reflects sounds much better than a roughr t‘fl C ° nvex surface is a very bad reflector of sound ; a flattltl) liirl 6CtS Vel T we ^ > kut a small degree of concavity, par-C ° l ' (! avb VV ' len the sounding body is in or near the focus of^lio j y> renders the surface a much better reflector, and theTliug considerably louder.

ln an elliptical apartment, if the sounding body be8 Pers 0n °" e focus, the sound will be heard much louder bya,| y s >tuated in the other focus of the ellipsis, than inPart of the room. In this case, the effect is so

“'anti

that even when the middle part of the

the sound expressed in one focus will be heard' s °n situated in the other, but hardly at all by those

>n the intermediate space.

j'Wmi^ 111 attempting to explain the manner in which the®8 bod° a,r ’ m P'nges upon, and is sent back by, the reflect-f^^tieg "'^ich would lead us too far into the science of’ "’e shall briefly notice the following ascertained

j j

Hi at ; J )erso n standing before a high wall, a bank, a rock,8 ,Sg v c . er tain distance, and uttering a word with a pretty^ ICe > or producing by a hammer, stone, &c., any\ ^>11 (f f ? Sou nd, hear a repetition of that word or sound,j. ri M, 0r ll( * that the time elapsed between his uttering the(1 C( lu a | str ‘king with the hammer, and hearing of the echo,tiNgh 0 l **e time that a sound is known to employ in goingH ''feiu! 1 , 1 . 1 ex tension of twice the distance between him andr ttiu^t" Ul ® ' v ‘ fl Mi rock, &c.; for the vibratory motion of the<a i Wk ^ l ° c eed from the sounding person to the wall, &c.,from the latter to the former. Now, sound0 p travel at the rate of about 1,125 feet in afH, or , 1 ^ IIrie ; therefore, if the person who expresses the

i i

Ho

Hta n f soun 4 whatever, stand at the distance of 1,125j, t ,e echoing wall, &c., two seconds of time musti* ‘ Jf' Veea his uttering the sound and his hearing theof ^' ie ^' s tance be equal to 4,500 feet, then eight"hr 1 and t |* lne mus t elapse between the uttering of the

arrival of the echo ; and so on. But the same■o er, t ,p lln ^ and the echo may be heard by persons atO hi,, lstatl ces, both from the original sounding-place, andIjojj hy -Acting body. The effect, however, will not be\ Wiq l . orin , for those who are nearer to the reflectingCS, io ‘ear the echo sooner than persons more remote.

I, A*e or' • na ^ r h e easily found, from which they will hear“• Hb ‘ginal sound and the echo at the same instant, and

iH coalesce, they will only appear as one loud

'C 1 CT ‘he echo.

^ flip „ several n

several persons, in different situations, may

i V* ‘ a oi ° ° "he same sound, yet the echo will be heard| Vf 8 hiii„, le particular direction than in any other: now ifcrip ‘ nes be drawn from the middle of a reflecting’ “ad tt!° *'he place from which the original sound pro-‘‘ e other to the above-mentioned best direction,

those two lines will be found to make equal angles with thesurface. Hence it appears, that in the reflection of sound,the angle of incidence is equal to the angle of reflection.Therefore, if a person wishes to hear the echo of his ownvoice in the best possible manner, he must stand in a direc-tion perpendicular to the reflecting surface. And this shows,that though sound proceeds from an original sounding body,or from a reflecting surface, in every direction ; yet a greaterquantity of it proceeds in some particular direction than inany other, which is probably owing to the original impulsebeing given to the air more forcibly in one direction thanin another, or from want of perfect freedom in the aerialfluid.

Several phenomena may be easily explained upon theabove-mentioned property of sound : for instance, severalreflecting surfaces are frequently so situated with respect todistance and direction, that a sound proceeding from a certainpoint is reflected by one surface first, then by a second, soonafter by a third, and so on, but by all in one direction ; inwhich case a multiplied tautological echo is produced; that isto say, the same word is heard repeated several times succes-sively in the same tone and accent ; the expression of oneHo ! will appear like a peal of laughter ; a musical instru-ment, properly played, will produce an agreeable repeti-tion of as many instruments of the same sort, imitatingeach other.

According to the various distances of the speaker, a reflect-ing object will return the echo of several, or of a few sylla-bles, for all the syllables must be uttered before the echo ofthe first syllable reaches the ear ; otherwise it will makea confusion. The farther the reflecting object is, the greaternumber of syllables will the echo repeat; but the sound willbe enfeebled nearly in the same proportion, till at last thesyllables cannot be heard distinctly. When the reflectingobject is too near, the repetition of the sound arrives at theear whilst the perception of the original sound still continues,in which case, an indistinct sounding noise is heard. Thiseffect may especially be observed in empty rooms, passages,&e., because, in such places, several reflections from the wallto the hearer, as also from one wall to the other, and then tothe hearer, clash with each other, and increase the indis-tinctness.

From what has been said, it will be easily conceived, thatwith respect to echoes, a vast variety of effects may be pro-duced, by varying the form, the distance, and the number ofreflecting surfaces; and hence we hear of various surprisingechoes being met with at different places.

In Woodstock Park, near Oxford, there is a famous echo,which repeats seventeen syllables in the daytime, and twentyat night, when the air is somewhat more dense. On the northside of Shipley Church, in Sussex, there is another remark-able echo, which, in favourable circumstances, repeats twenty-one syllables. At Rosneath, near Glasgow, in Scotland , isan echo, that repeats three times, completely and distinctly,a tune played with a trumpet.

Whispering-places, are those where a whisper, or othersmall noise, is conveyed from one part to another, at a greatdistance. They depend upon this principle, that the voice,being applied to one end of an arch, easily passes by a repe-tition of reflections to the other.

Hence sound is conveyed from one side of a whispering-gallery to the opposite one, without being perceived by thosewho stand in the middle. The form of a whispering-galleryis that of a sphere, or the segment of a sphere. The principleof whispering being that of continued reflection. If a personwhisper softly against a wall, the rays which proceed from hismouth issue in all directions against the wall; we shall only

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