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Show bluff, or reflecting surface, and hack the aama dletanoe. will be leea than one-fifth of a second. If the dla-Itance dla-Itance be greater than Ilk feet the I sound wkve will be longer than the fifth of a second In going and coming, com-ing, ao each bound uttered will be I echoed back distinctly. Walla of rooms do not echo back aoundk. for the dlatanca. la leak than lit feet, but In Urge balls aoundk produce reverberatlona. Reverberatlona are not heard 'in a furnlthed room be-cause be-cause the furniture breaka up the eouad waves. la the atethoocope which doctors preea agalnat our bodlea la a diaphragm, dia-phragm, not unlike the drum of the ear. only more aeneltlve to kound wkvea Bound wavea produced by the heart-beat eeuae the diaphragm to vibrate: hence, the vibrating diaphragm dia-phragm klarta aound wavea (a new acrleel In the air of tba atethoocope which, reflecting back and forth between be-tween the walla of the tubea. be-oome be-oome concentrated and therefore audible la the doctor's ear. Fireside Science By Ransoms Sutton Coprrlsht. IMS tf.' T. (.vesta Weriai, Press ruMlokias e. aHfaUir DAY FHYilCkl SOCHD. In Ilka manner aa heat and light krk caused by waves In sther the redlant eubatance which filla all space aound la produc-d by wavea la gaaee inks the air), la Uqulde and In aolldk, Tba moleculea of the medium do not mova with the wevee; like keaweeda In water, they are crowded together by the coming com-ing of the wave, bot aettle back Into their former poaltloaa aooa kfter the neve haa paeeed. The moleculea next to the source of the sound feel the agitation first; they bump agalnat their neighbors, the neighbors neigh-bors pkaa on the bump, knd the bumping contlnuee down the line, with diminishing violence, until the energy Imparted at the aource of the agltatloa becomes exhausted. ' Mow. If thla wave emovemer.t reaeee before falling upon the auditory au-ditory organa of an anlmaL no aound la produced: for sound la a brain aenaatloa end If no braia be within hearing dlatanca the wavea die dowa without atlmulallng tha aenaatlon. The wavea exlet. but sound le lacking. .... But becauae human ears fall to hear aoundk tk no Indication that the kounda may not be beard by other ereaturee. Our ear druma respond re-spond only to wavea which are neither too long nor too short. The very short eeund wavea like the very short light wavea which paae by ua saheeded. probably produce aenaatlona In the bralaa of Inaerta Ineecta may bo deaf to our sounds, but they ara thought to have a whole aerlee of their owa, ts which we ara deaf. Kouad wavea travel In air at a apeed of 1100 feet per aecond; in water, at feet per second: In oak. at It. at feet per aecoad: In steel, at 1I.0OS feet per aecond. Like light and heat. aound wevee apread out In all dlrectiona from the source, diminishing In .Intensity with the equare ar tha dlatanca. Tea caa hear four tlmea aa wall at ton feet kk kt 0 feet. Because eouad wavea travel better. bet-ter. through aleel than air. work-men work-men aloag railroada put their eara en tha ralla when listening for trains Thar could sear it rour-teen rour-teen Mmea further awav by rail thaa by air. If the ends' the rails were welded together. It you tap a atone In tba cellar, no sound Is heard upstairs, but If yen tap a eteam pipe, the aound carries Into every room through which ths Pipe ixactlr Ilka light waves aound wavea may bs reflected. The reflected re-flected wave, whea It cornea bank to our ears, ts railed aa echo. Rrboea cannot be beard If the reflecting re-flecting eurfaro is os near, for the human ear cannot dlatlnguleh betweea waves which corns mors rapidly thaa five par aecond. Reverberations Re-verberations reeulL If more tkas, five aouad wavee per ascsad heat upon the ear drum. - rnriiii tha fifth of a second a !wsve length will travel JJS feet In elr (one-fifth of lis feet, the distance eouad waves travel er second). sec-ond). Hence, If the reflecting sur-fece sur-fece be lees hsn W feet awav. the eouad wave It throws PTrk will produce as echo; for the time It takes ths wavk to go out to ths |
