Page:Popular Science Monthly Volume 91.djvu/927

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Popular Science Monthly

��911

��machines faithfully. The high speed of the

wind is identical with the actual flying

speed. Arrangements for slowing and

accelerating the air, smoothing its flow,

measuring its

speed and

impact, and

eliminating

resistance

other than

that offered

by the object

under test

are provided.

In such a tunnel the model to be tested does not move. It is rigidly fastened in place. Only the artificial wind moves. But the results obtained are exactly those that would follow if a full-sized model were made to fly in a wind of known strength.

Not only have models of aircraft been tested, but the air-resistance of ships c?n now be ascertained.

���The windtunnel forms a circuit flattened out like a chain link. There is practically no resistance to the blast of air

��Filtering Out the Harsh Tones from a Phonograph

A PHONOGRAPH cabinet calculated to sift, correct and beautify sound before it is thrown to the atmosphere, has been invented by Henry C. Miller of Saratoga, New York. The inventor's principal object is to correct the defects in some of the tones which are unduly magnified by the horn or amplifier. The operative prin- ciple of this cabinet will be better understood when it is made clear just how and where a tone is changed from true to false in your phonograph be- fore it reaches the atmosphere. Assuming all sound vibra- tions recorded in the grooves of the disk to be true and that they are now passing before the needle to be transmitted through the reproducer into the horn, it is noted that a certain tone is unduly magni- fied. If the horn is now substi-

��tuted for one of a different volume and the record started over again, the defective tone will assume its proper value. But in so doing it will also be found that a different

tone in the selection has been improperly reproduced. Why? Be- cause the horn which serves to magnify all sound direct- ed through it, is in itself tuned to a certain key by virtue of its size, shape and weight, and readily responds to vibrations of a tone to which it is keyed. Have you noticed that when a certain note on your piano is struck some object in the room vibrates with it in sympathy and produces a harsh effect? In a phonograph this sympathetic keying results often in undue amplification of an unimportant tone.

In this new cabinet the sound, instead of being directed from the horn to the atmosphere, is thrown downward into the open ends of a series of sympathizers and resonators, each care- fully keyed to vibrate in sympathy with a different tone. It is, of course, necessary to provide enough sym- pathizers to corre- spond with every tone (sharp and flat) in the musical scale.

When a record is played on this phono- graph, each tone of the selection will set into vibration the par- ticular amplifier which has been tuned to cor- respond with it. Thus every tone will re- ceive equal amplifica- tion relatively to fit its original value be- fore it is finally thrown on the air.

���The sound is thrown downward upon carefully keyed resonators

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