Page 19 - Summer 2008

Fig. 3. Detail of a portrait of Giovanni Battista Venturi painted by Prospero Minghetti in 1818 (reproduced by kind permission of the Musei Civici, Reggio Emilia). In the 1790s Venturi conducted experiments on sound localization while blocking one ear with his finger.
a great measure upon a new impression being made upon the auditory nerve by one sound, before the impression of the sound immediately preceding has passed away.”17 Wells did not conduct such experiments, but reached his conclusions on the basis of his observations of binocular color combination. His remarkably prescient prediction concerning the presen- tation of two streams of tones in alternation at the two ears has only recently been examined, as will be detailed below.
Venturi (Fig. 3) was born near Reggio Emilia; he became professor of physics at Modena and Pavia and is best known for his work on fluid mechanics. His studies of Leonardo da Vinci’s manuscripts resulted in a radical revision of the artist’s
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auditory localization using one or two ears. He had exam-
ined binocular color combination with blue and yellow papers, and arrived at a firm conclusion: “I have never expe- rienced a third color from the two overlapping colors.”19 In his experiments on auditory localization he compared listening with both ears to listening with one ear blocked by a finger. He concluded that spatial localization was only possible with both ears, and he surmised that this was based on amplitude differences between the two ears: “Therefore the inequality of the two impressions, which are perceived at the same time by both ears, determines the correct direction of the sound.”20 Venturi’s experiments were essentially repeated and con- firmed by Lord Rayleigh (1842–1919), although Rayleigh
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in electricity, measuring its velocity and devising a bridging means of measuring resistance. In the context of perception, he is best known for his invention of the stereoscope, though
Venturi wrote extensive- ly about optics and its history, and it is in an appendix to one of his monographs on color that he described experiments on
scientific and technological genius.
appeared to have been unaware of them.
Wheatstone (Fig. 4) is famous particularly for his work
the other ear only, we could have little or no perception of har- mony from such sounds; and that, if any succession of sounds emitted by one instrument, we were to hear the 1st, 3d, 5th , and so on, by one ear only, and the 2d, 4th, 6th, and so on, by the other ear only, we should be deprived, in a considerable degree, of the melody of such sounds, as this seems to depend in
Fig. 4. Left–“Stereoscopist” by Nicholas Wade. Charles Wheatstone is shown with his eyes in the mirrors of his stereoscope. Wheatstone’s portrait is derived from an engrav- ing in The Illustrated London News marking the award of his knighthood; the diagram of the stereoscope is taken from Wheatstone’s original article.26 Right–Wheatstone’s diagram of a simple binaural instrument of his invention that he called a microphone.27 He wrote: “The greater intensity with which sound is transmitted by solid rods, at the same time that its diffusion is prevented, affords a ready means ... of constructing an instrument which, from its rendering audible the weakest sounds, may with pro- priety be named a Microphone.”
18 Acoustics Today, July 2008