144 ON THE SENSES. 



to a small reservoir of fluid, in which fluid again the undulatory movement is 

 reproduced, and that peciiliar excitation of the extremities of the auditory nerve 

 bathed by this fluid is exerted, which hurries to the brain the mysterious cur- 

 rent so often spoken of, and there, through the terminal apparatus of the nerve, 

 gives rise to the phenomenon recognized as a perception of sound. Thus long 

 is the chain of successive movements between their origin in the vibration of 

 the string and their termination in the inscrutable process by which the result 

 is communicated to the mind. As far as the nerves wex;an analyze these move- 

 ments through their entire course : l^p to the tympantim with great exactness, 

 inside of the ear with less precision ; but the movement within the nerve and 

 its result, the sensation, are two riddles, of which only the first aff'ords some 

 glimpses towards a solution, the second is, perhaps for all time, shrouded for us 

 in impenetrable obscurity. We are just as little in a position to define the na- 

 ture of a sens-ation of hearing, or any intrinsic and essential characteristic per- 

 taining to it, as we are in regard to an impression of any of the senses ; the 

 utmost we can do is to designate by commonly received names the qualities 

 of the sensations generated by certain causes, upon the supposition that the 

 sensation itself is known to every one from experience and an idea of its quality 

 impressed upon the memory. If we would more exactly describe the sort of 

 sensation which we call " high " or " shrill," instead of any distinctive token 

 of the sensation itself, we assign the nature and specific properties of the exter- 

 nal cause which excites it ; we designate a sound as of certain '' pitch," accord- 

 ing to the number of vibrations of the body producing it, or as of a certain tone, 

 according to the kind and peculiarities of the object or instrument from which 

 it proceeds, because we are, for the most part, incapable of giving an accurate 

 physical account of the forms of the undulations on which the modifications of 

 the sound are conditioned. The same holds good respecting the "strength" of 

 the sensation ; the sensation itself admits not of measurement, but we can meas- 

 ure the magnitude of the vibrations or the force of a mechanical arrangement 

 for producing them. In general, and in relation to each of these qualities, the 

 sound evades every attempt to analyze it, however distinctly the sensation may 

 present itself to our consciousness, however vividly we may be able to represent 

 it to ourselves without the presence of its exciting objective cause, however ac- 

 curately a practiced ear may seize the finest shadings of the height, the tone 

 and the strength of different sounds. It was necessary to premise these expla- 

 nations in order to reduce what is proposed by of the following exposition to a 

 proper standard. It is undoubtedly a legitimate problem for physiology to inves- 

 tigate the nature and origin of sounds in the exact sense which we have indicated, 

 but, for the solution of this problem, it is wholly unprepared ; the physiology 

 of the sense of hearing, of which we shall endeavor to give a brief and intelli- 

 gible sketch, can teach us at present nothing further than the ways by which, 

 and the forms in which, those motions of matter, which physical science has 

 shown to be the cause of the perception of sound, penetrate to the auditory 

 nerves ; the acoustical significancy of the complicated apparatus with which 

 nature has endowed our organism for receiving the impressions corresponding 

 to those motions ; and, lastly, the relation between the qualities of these exter- 

 nal movements and the qualities of the sensations as indicated by certain epi- 

 thets applied to them. We proceed to our task. 



Deep within the skull, enclosed on each side by the so-called petrous bone, 

 the auditory nerve spreads its peripheral extremities, secluded from all immediate 

 contact with the air, which brings to us, in propagated waves, the sound pro- 

 ducing vibrations of bodies whether near or distant. Of possible ways in which 

 pulsations of the surrounding air might be conveyed to the auditory nerve there 

 are many ; but one is suited beyond all others to this office, and alone aff'ords, 

 by an arrangement pre-eminently adapted to the conveyance of sound, an 

 adequate guarantee for the arrival of even very weak undulations at the per- 



