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 



