Elements of natural philosophy (Volume 2-3) . h the first medium. cause of this This division of an original pulse into two others, arises resolution. entirely from the reciprocal action of the two media on each other. If the media be perfectly elastic, there can be no loss of living force, and the sum of the intensities of sound in the component pulses will be equal to that of the original pulse. If the media be not perfectly elastic, there will be a loss of living force, and the sum of the intensities of the component pulses will be less than that of the original pulse. incident, The origina
Elements of natural philosophy (Volume 2-3) . h the first medium. cause of this This division of an original pulse into two others, arises resolution. entirely from the reciprocal action of the two media on each other. If the media be perfectly elastic, there can be no loss of living force, and the sum of the intensities of sound in the component pulses will be equal to that of the original pulse. If the media be not perfectly elastic, there will be a loss of living force, and the sum of the intensities of the component pulses will be less than that of the original pulse. incident, The original pulse is called the incident; that transmit- rcflTcte^p^sts. ted into tlie second medium, the refracted; and that driven back through the original medium, the reflected pulse. Ech0 To an ear properly situated, the reflected pulse will be audible, and is, for this reason, called an echo. The sur- ELEMENTS OF ACOUSTICS. 79 face at which the original pulse is resolved into its two v&viatincomponent pulses, is called the deviating §72. To find the law which regulates the direction of Dircctionoftnethe reflected pulse; let A If be a _. ^ TmS portion of the front of an incidentspherical pulse, so small that it maybe regarded as a plane. Draw If A\Ar iVand A 0, normal to the pulse,and suppose the latter, movingin the direction from iVto A\ tomeet the face E G of a second me-dium. Each molecule of the pulseas it recoils from the surface E G,becomes the centre of a divergingspherical pulse which will, Eq. (28),be propagated with the velocity of the incident pulse. Accordingly, when the portion IfExplanation andreaches the face of the second medium at A\ the por-ction A will have diverged into a spherical pulse whoseradius is A B = A M. In like manner, if A M bedrawn parallel to A M, the portion diverging from A!will, in the same time, have reached the spherical pulsewhose centre is A! and radius A! Bf = A! N. The sameconstruction being made for all the points of the inciden
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