. Diseases of the ear; a text-book for practitioners and students of medicine. ng sounds which shall alwaysbe uniform both in pitch and intensity, is probably the mostsimple of these devices. The principle of the telephone hasbeen used in constructing instruments for this purpose. Ofthese, probably that recommended by Urbantschitsch f is thebest. The operation of this instrument and of other kindreddevices depends upon gradually diminishing the intensity ofa given sound by sliding the secondary coil of an inductionapparatus, introduced into the circuit, over the primarv coil. * Archives of Oto
. Diseases of the ear; a text-book for practitioners and students of medicine. ng sounds which shall alwaysbe uniform both in pitch and intensity, is probably the mostsimple of these devices. The principle of the telephone hasbeen used in constructing instruments for this purpose. Ofthese, probably that recommended by Urbantschitsch f is thebest. The operation of this instrument and of other kindreddevices depends upon gradually diminishing the intensity ofa given sound by sliding the secondary coil of an inductionapparatus, introduced into the circuit, over the primarv coil. * Archives of Otology, vol. xvii, p. Lehrbuch der Ohrenheilkunde, Vienna, 1S90, p. 146 FUNCTIONAL EXAMINATION. The sound is conveyed to the ear of the patient by means ofan ordinary telephone. In the instrument shown in Fig. 60 the sound employed isproduced by the rapid interruption of the electric current byNeefs hammer. It is necessary that the vibrating hammerbe completely inclosed, in order that its repeated blows maynot be heard through the air in cases where the hearing is. FlG. 60.—Urbantschitschs electric acoumeter. E, Primary battery ; IV, Neefs ham-mer for interrupting the current automatically, and thus producing the sound tobe employed in conducting the test ; 2, 2, Induction coils of equal size, butwound in opposite directions ; I, Movable helix ; T, Telephone ; S, Screw formoving the helix. As the helix is withdrawn from one secondary coil, it entersthe other, which is wound in the opposite direction, and the intensity of thesound heard through the receiver is thus increased or diminished at will. (Ur-bantschitsch.) but slightly impaired, or by the opposite ear, where there isgreat impairment upon one side, the opposite organ beingnormal or nearly so. A somewhat similar instrument has been devised by Gra-denigo,* in which the source of sound is a metal rod producinga pure musical note corresponding to C in the musical scale. * Handbuch der Ohrenheilkundep. 383. Schwa
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