The Pharmaceutical era . des may hold conversation without be-ing heard by those who are stationed between. Refraction and Diffraction of Sound.—By the refraction ofsound is meant the change in direction caused by the en-trance into or passing through a medium of differentdensity. If between a source of sound, as a watch, andthe ear there may be interposed a thin balloon filled withsome dense gas, as carbon dioxid, the sphere of gas willoperate as a double-convex lens and cause the soundwaves to converge to a focus on the opposite side, wherethey will be heard more distinctly than at interveni
The Pharmaceutical era . des may hold conversation without be-ing heard by those who are stationed between. Refraction and Diffraction of Sound.—By the refraction ofsound is meant the change in direction caused by the en-trance into or passing through a medium of differentdensity. If between a source of sound, as a watch, andthe ear there may be interposed a thin balloon filled withsome dense gas, as carbon dioxid, the sphere of gas willoperate as a double-convex lens and cause the soundwaves to converge to a focus on the opposite side, wherethey will be heard more distinctly than at interveningpoints, the curvature of the waves being reversed intheir passage through the denser gas. (Fig. 43.) ?WTieh sound waves strike the edge of an obstacle, sec-ondary waves are set up which pass behind the object,so that the latter only partially forms a sound bending of the waves around a corner is called Dif-fraction. Difference in Sound Sensations.—Sound sensations differ inLoudness, Pitch and Fig. 43.—Refract swing on each side of a middle line. Since amplitude orlength of swing depends upon the energy of the soun«lTibration, loudness may be said to depend upon the en-ergy of the sound vibration. The more energy the latterpossesses, the harder the impact it makes upon the or-gan of hearing, and hence the stronger the sensation. Effect of Distance on Loudness.—As previously stated, soundwaves advance in the form of ji sphere which continual-ly grows larger as the point of origin is receded from,consequently the intensity of the sound must continuallydiminish. Since the surface of a sphere varies as thesquare of its radius, i. e., that doubling the radius in-creases the surface of the sphere four times, it followsthat doubling the distance from the origin of a sounilmust diminish its loudness to one-fourth, because thesame volume of sound is now spread over four timesthe area, or, as the law is commonly expressed. Loud-ness, or intensity, varies I
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