The outlines of physics: an elementary text-book . ere moving, weshould find that, instead of being everywhere equallydense, there are successive layers of great density (d, d,Fig. 307), with intervening layers (r) where the air is rarefied. The vibration , ^ of the air is momenta- ?? « rily in the directions of the small arrows, thus producing condensation at d, d, and rarefaction ^^^- ^^? at r. These regions of condensation and rarefaction all move simultaneously in the direction of the large 338 THE OUTLINES OF PHYSICS arrow, without changing their positions relative to oneanother. 303. Sou
The outlines of physics: an elementary text-book . ere moving, weshould find that, instead of being everywhere equallydense, there are successive layers of great density (d, d,Fig. 307), with intervening layers (r) where the air is rarefied. The vibration , ^ of the air is momenta- ?? « rily in the directions of the small arrows, thus producing condensation at d, d, and rarefaction ^^^- ^^? at r. These regions of condensation and rarefaction all move simultaneously in the direction of the large 338 THE OUTLINES OF PHYSICS arrow, without changing their positions relative to oneanother. 303. Sound Waves produced by a Projectile.—Projectilesmoving at high speeds produce air waves which are similar to those by meansof which sound istransmitted andwhich travel at thesame velocity. In-stantaneous photo-graphs of such pro-jectiles show diagram in is from a photo-graph of a rifle bul-let in flight, takenby Mr. C. V. Boysin England. Theoblique lines, a, a,b, b, show thepositions of theFig. 308. 304. The Velocity of Sound. — It has been seen in theexperiment of the sensitive flame that sound waves travelwith a high velocity. It is only necessary to recall thefollowing observation, which every one will have had fre-quent opportunity to make for himself, to show that thisvelocity is very much less than the velocity of light. Ifwe watch a distant railway train when the whistle issounded for a crossing or station, we may notice that thepufE of steain is followed only after a very considerable THE PROPAGATION OF SOUND 389 interval, depending on our distance from the engine, bythe sound of the whistle. The sight of the puff of steamhas been conveyed to the eye by means of a wave of light;the sound, however, which occurs simultaneously with thesetting free of the steam, by a sound wave. The intervalof time which seems to elapse between the two is thereforethat which the sound wave requires to traverse the spacebetween the whistle and the ear of the obs
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
