[History of the tuning fork. II: Evolution of the classical experiments by Weber, Rinne and Schwabach].
BACKGROUND: Since the 17th centrury it was known that sounds could be perceived via air conduction and bone conduction and that this provided a means of differentiating between hearing disorders located in the middle ear and those located in the acoustic nerve. For a long time to come, however, there was no need for such a differential diagnosis. After the invention of the tuning fork in 1711 this instrument had soon become widely used in music, but it took well over 100 years until it was introduced into physiology and otology. FROM DIRECTIONAL HEARING TO WEBER'S TEST: J. B. Venturi, a physicist in Modena, Italy, in 1802 had shown that the perception of the direction from which a sound is coming is governed by the fact that one ear is hit by the sound more intensely than the other ear. C. T. Tourtual, a physician in Münster, Germany, demonstrated in 1827 that this also holds true for sound conducted via the skull bones. He used a watch as sound source. He found that occlusion of both ear canals would increase the sensation in both ears equally, but that occlusion of only one ear would increase the sensation only in the occluded ear, thus giving the impression that the sound were coming from that side. He was interested in a comparison between vision and audition, and he concluded that with regard to recognizing the direction of a sensory signal vision was superior to audition. In the same year 1827 C. Wheatstone, a physicist in London, investigating the mode of vibration of the tympanic membrane and using a tuning fork found the same phenomena as Tourtual and some more effects. E. H. Weber, an anatomist and physiologist in Leipzig, Germany, described the very same phenomena as Tourtual and Wheatstone once more in 1834. He wanted to prove that airborne sound is perceived by the vestibulum and the semicircular canals, bone conducted sound by the cochlea. None of these investigators was thinking of a clinical use of their findings and made no such suggestion. E. Schmalz, an otologist in Dresden, Germany, in 1845 introduced the tuning fork and the test later named after Weber into otology and explained in great detail all possibilities of a diagnostic evaluation of the test. His grand achievement, however, passed unnoticed at his time. THE RINNE TEST: A. Rinne, a physician in Göttingen, Germany. In 1855 described the test which later was named after him, in an elaborate treatise on the physiology of the ear. He wanted to demonstrate that in man and animals living in the air, as opposed to those living in water, the conduction of sound via the bones of the skull is just an unavoidable side effect of sound perception. He mentioned a clinical application of his test only in a footnote and obviously never used it himself in a systematic way. His test was made generally known by Lucae in Berlin only after 1880. The value of Weber's and Rinne's tuning fork tests was much disputed even at the turn of the century and only gradually became generally accepted.