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ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1908. 



Fig. 19. — Parson's sound box. 



but by means of which sound records of the Berliner type can be 

 most effectively reproduced. In this machine the record does not 

 vibrate a diaphragm, but it vibrates a very finely adjusted valve 

 which controls the flow of a column of air under pressure. As the 

 air passes through the valve there are given to it minute pulsations, 



Avhicli correspond to the 



undulations in the 

 sound record, so that 

 sound waves identical 

 Avitli those originally 

 recorded are set up in 

 the surrounding air and 

 travel to the ear of the 

 hearer. 



In the apparatus joii 

 see here (fig. 15), a one-sixth horsepower electric motor drives an air 

 compressor. The air, after passing through an oil separator or filter, 

 enters a reservoir, which helps to insure a regular flow of air to the 

 valve. From the reservoir the air passes through a dust collector 

 before it reaches the valve, as the very fine adjustment of the latter 

 is apt to be interfered with if particles of dust or oil get into it. 



The sound box, as 

 you will see on refer- 

 ring to the drawing, 

 comprises a vibrating 

 comb or grid valve, 

 rigidly connected to 

 the stylus bar or needle 

 holder, and a grid 

 valve seat. The valve 

 is on the side of least 

 pressure, and is carried 

 by a spectacle spring 

 (58, fig. 18). The air 

 is deflected to the walls 

 of the sound box by a 

 conical deflector, so 

 that it reaches the 

 whole of the surface of 

 the valve at uniform pressure. A resilient rubber washer holds the grid 

 valve normally against the valve seat. As the needle moves, following 

 the sinuosities of the sound line, the valve moves with it, and thus 

 opens and closes more or less the slots in the valve seat through which 

 the air is rushing. The effect of this I will let you hear for yourselves. 



Fig. 20. — Note of orchestra : 0.5 second. 



