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Dr. B. W. Richardson on the Audiometer. [May 15, 



In using the instrument, the induction coil is moved along the scale 

 from or towards the larger primary, as may be required, and the 

 degrees or units of sound are read from the figures on the scale, the 

 sound being made by the movement of the microphonic key between 

 the battery and the primary coils. 



The person whose hearing is being tested should sit in an easy 

 position, and should not see the act of the observer in moving the 

 microphone key. For good observation, the room in which the 

 experiment is made should be large, and all external causes of sound, 

 such as the ticking of clocks, the vibrations of windows and doors, the 

 moving of feet and the singing from gas jets, should be silenced. The 

 sitter should close the ear that is not applied to the telephone while 

 he is listening for minute sounds, and should give his full and calm 

 attention to the proceeding. Any excitement is like to lead to error 

 when refined measurements are required. 



Capacity of the Instrument for Observation, 



The instrument may be considered to afford the most satisfactory 

 means for testing the hearing power of all persons who can define 

 a sound. The range of sound is sufficient at the maximum — 200° — 

 for everyone who is not absolutely deaf ; 0°, or zero, is a point of 

 positive silence from the instrument, or rather from the sound which 

 it produces through the telephone. 



Phenomena from Observations made on different Persons. 



Abrupt Loss of Sound. 



One of the first facts learned with the audiometer is the sudden- 

 ness with which the sound is lost to those who are listening. The 

 sound is abruptly lost within a range of 2° ; that is, within one- 

 hundredth part of the entire scale. This is the case with those who 

 are very deaf as well as with those who hear readily, a fact originally 

 noticed by Mr. Hughes, and which I have corroborated by fifty special 

 observations on different persons presenting powers of hearing which 

 varied from 200° to 140° as the extreme limit or capacity, to complete 

 hearing through the whole scale, down to zero. In these persons, 

 when the observation was taken, under the strictest possible conditions 

 for surrounding silence, the point between distinctness of sound and 

 complete loss of it was not more than one-hundredth part of the scale. 



Continuous Hearing in Line. 



In testing the capacity of hearing, it is noticeable that the power to 

 detect the diminishing sound is maintained best by continuing the 

 reduction in trace or line while the attention is fixed. A sudden break 

 may cause the sound to be lost to the listener long before his real inca- 



