Underwater t. V. Camera

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In recent years underwater television has been introduced as an aid in the study of the ocean and underwater work. Apart from a few special features an underwater camera is based on the principles of ordinary T. V. cameras.

At present there are several types of underwater cameras to be operated chiefly at depths from 650 to 1,000 feet.

Connected to the viewing screen by a long flexible cable, the camera can be easily lowered by a crane and moved about. The cable connects the camera to its control equipment. A special intercommunication system is used for the diver to keep in touch with the control personnel.

The T. V. camera can be used for underwater exploration of marine life, television broadcasting as well as for inspection of canals, dams, turbine blades, and ships.

A tape recording may be made of the television picture for a permanent record. This makes possible underwater photography without film.

TEXT 8 C

Wave motion and sound

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Wave Motion. - One of the most important phenomena in nature is the transmission of energy from one point to another by wave motion. This kind of motion is illustrated in many ways. When a stone is dropped into a pool of still water, the surface of the water is covered with circular wavelets which widen out from the central point where the stone fell. The water does not really move outward from the central point, but it rises and then falls again. That such is the case is seen by observing a floating leaf or piece of wood. It does not move forward but returns again and again to its former position. Hence, the water on which the leaf rests must have this same kind of upward and downward motion rather than a forward motion.

When one end of a rope is fastened to a rigid wall the free end moves up and down rapidly, each jerk travels along the rope, each portion of the rope communicating the jerk to the next portion. Each particle of the rope imparts its upward or downward motion to its neighbors. The jerk moves forward, but the particles of the rope move only up and down. Motions of this kind are wave motions, in all these cases it is evident that there is a vibrating center which produces motions in those portions of the medium immediately in contact with it, and that these portions impart their motions to the neighboring portions.

Nature of Sound. - The source of sound is always in a state of vibration. As the vibration dies down, the intensity of the sound diminishes. If a ringing bell is touched with the fingers, the sound ceases because the vibrations are stopped by the fingers. When a weight falls to the floor, the weight as well as that part of the floor which is struck are set in vibration, and sound waves are produced. If a stretched guitar string is plucked, it gives a musical note owing to the vibrations set up in it. These vibrations take place too fast for the eye to follow them, and the string seems to be drawn out into a ribbon in the middle. In a vibrating tuning fork the prongs alternately approach and recede from each other. These movements of the prongs can be felt by touching the prongs with the fingers. They produce compressions and rarefactions in the surrounding air that travel forward as sound waves.

Velocity of Sound. - The velocity of sound depends on the density and the elasticity of the medium. The greater the elasticity and the less the density, the greater is the velocity. The relation between the velocity, the density, and the elasticity of the medium is expressed by the formula

Where v = the velocity of sound

e = the modulus of elasticity of the medium

p = the density of the medium

The Intensity of Sound. - When sound waves spread out in every direction from a source of sound, the intensity varies inversely as the square of the distance from the source. In this case, the sound waves spread out as spheres. The same amount of energy is transmitted across every spherical surface having its center at the source of sound. The larger the surface of these spheres, the smaller the energy that goes through each square centimeter of surface. The surfaces of these spheres increase as the squares of their radii. Hence, the energy that passes through unit area decreases as the squares of the radii increase.