Exposition. Fundamentals of Acoustics

Describes the modification of sound waves be- tween the source and the hearer and portrays the physiology of hearing. Animation illustrates the principles of velocity, refraction, range of hearing, lowering intensity, attenuation in air, eliminating high and low frequencies, reverbera- tion, and focusing. Sound effects clarify the animated action. Reference is made to the ad- vances in communication coming from an in- creased knowledge of sound and electricity. Gravitation of Liquids. 16si. Bray. First two, then five are liquids shown to possess definitely different densities.