The mechanism of the ossicles of the ear and membrana tympani / by H. Helmholtz ; translated from the German, with the author's permission, by Albert H. Buck and Normand Smith.

  • Helmholtz, Hermann von, 1821-1894.
Date:
1873
Catalogue details

Licence: Public Domain Mark

Credit: The mechanism of the ossicles of the ear and membrana tympani / by H. Helmholtz ; translated from the German, with the author's permission, by Albert H. Buck and Normand Smith. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Finally, it is necessary, at least for the deeper and middle tones of the scale, that there should be an equality of pressure between the air contained in the middle ear and that of the ex- ternal auditory canal. In the case of very high tones, those corresponding to the highest octave of the piano, the length of the auditory canal is very nearly equal to a quarter of a wave's length, to which circumstance is due the occurrence of those phenomena of resonance described by me in the Lehre von den Tonerwpjmdungen* At all events, the diameter of the exter- nal auditory canal is too small to permit of different phases of pressure or of speed at different points of the membrana tym- pani at the same moment, and we can, therefore, without hesita- tion consider the pressure as equal at all times over all parts of the membrane. This circumstance is likewise of great impor- tance in the mechanism of the ear, for it excludes all possibility of one part of the membrana tympani being excited, while the rest is not; the part excited being dependent on the locality of the sound-giving body. Hence we have no other means of localizing sound except by noting the different degrees of intensity obtained by changing the position of the head and comparing the impressions made upon both ears. The above-mentioned rule applies, as already stated, to bodies none of whose linear dimensions are infinitely small compared with the rest, consequently not to strings, membranes, rods, and disks. It is also liable to exceptions, as where the middle por- tion of the body in question is contracted and very narrow. Among the component parts of the auditory apparatus, the mem- brana tympani is the only one which falls under the head of exceptions. In point of fact, those bodies which are very thin at one spot, or in one direction, are capable of performing com- paratively slow vibrations; for, owing to their slight thickness, they offer but a feeble elastic resistance, return slowly to a state of equilibrium, and vibrate at a much slower rate than is the case with oscillations in thick masses of the same nature. That the bones of the ear do not come under the head of ex- ceptions, is easily shown by comparing them with the metallic rods or tongues which are used in the production of high tones. * Pages 175, 17G.