THE SENSE OF HEARING. 171 



the source of sound outside of our own ear, but the sound — that is, the sensation 

 itself, with all its qualities; that we think the sound penetrales as such from 

 ■without through the portals of hearing to our soul. The newly-born child hears 

 like the grown man, has the same quality of sensation, but he knows not whence 

 the sound comes, knows not that it comes from without, or, indeed, that there is 

 anything without him. It learns gradually to distinguish outer objects from its 

 /, its Ego, and thus comes gradually to recognize the cause of the sensation of 

 sound as something existing outside of itself We have, as a general thesis, 

 discussed in previous essays on the senses the process by which this objectivity 

 is made familiar to the human mind ; we shall here, therefore, only consider the 

 method in which the process is specially conducted as regards the sense of 

 hearing. A fact which at once guides us to a right point of view is this : that 

 only under a certain condition do we conceive an outward object to be the cause 

 of the sensation of sound, and when this condition is wanting, seek the source 

 of the sensation within ourselves, even when we know and are directly informed 

 by other senses that it lies without us ; that condition is, that the sound shall be 

 conducted to the auditory nerve through the channel which we have been above 

 anatomizing, the outward ear, the tympanum, and the ossicles. If by any means 

 whatever the transmission of the air-waves to the tympanum and the vibration 

 of the latter be prevented, every sound which, being conducted by the ossicles, 

 reaches the auditory nerve with sufficient force, seems to us to originate within 

 ourselves. This is most readily and strikingly shown by immersion in water. 

 According to the researches of one of our most ingenious physiologists, the tym- 

 panum under water only so long conveys the waves of sound, or propagates their 

 oscillations to the labyrinth, as the external passage of the ear is filled with air ; 

 if it be filled with water, so that the outer surface of the tympanum is bathed by 

 it, the transmission of waves of sound takes place only through the ossicles or 

 movable bones ; but with considerable intensity, since the bones, though as solid 

 bodies they take up with difficulty sound-producing undulations of the air, take 

 up with facility sound-producing undulations of the water. If now, while one 

 is immersed, a sound under water be caused by another person, as, for instance, 

 by striking two stones together, this sound, so long as the auditory canal con- 

 tains air, will be ascribed to an external source, and its direction be correctly 

 determined ; but so soon as the passages of the external ear are filled with water, 

 the sound, from whatever direction it may proceed, will seem to originate within 

 the head. The experiment may be variously modified ; and since in the form 

 just described it is somewhat inconvenient, the following method may be resorted 

 to : let the inquirer modulate his voice to a tune, and while continuing to do so, 

 suddenly close both ears firmly with his hands ; immediately an entirely difierent 

 sensation will ensue, the tone of his own voice, which, with the ears open sounded 

 as if from without, will on the instant of the closure seem to arise from within. 

 Since it cannot, then, be doubted that the vibrations of the tympanum in some 

 manner determine the objectivity of our impressions of hearing, it is worth in- 

 quiring what part that instrumentality plays. The most probable conjecture is 

 the following : the tympanum is very richly provided with nerves of feeling, 

 which, like the nerves of touch of the rest of the surface of the body, are adapted 

 to sensations of touch and of common feeling ; these nerves are thrown into ex- 

 citation when the tympanum vibrates, and generate a sensation of touch, of the 

 quality of which we are not specially conscious, because it is, as it were, dulled 

 by the sensation of hearing which constantly accompanies it, but which, like 

 every impression on the skin, is associated with the idea of an external object as 

 the exciting cause. As we refer this idea obtained through the nerves of touch 

 to the simultaneous auditory sensation, and, indeed, falsely identify it therewith, 

 we arrive at a perception of the objectivity of the source of sound, without being 

 aware of the circuitous manner in which we acquire it. Here is again an ex- 

 ample how one sense comes to the aid of another, how two perceptions of sense 



