170 ON THE SENSES. 



the sense. At first glance, perhaps, this fact may not seem very singular ; not 

 more so than the simultaneous perceptions of other organs — the skin and the 

 eye. Innumerable impressions on the skin are simultaneously perceived, and, 

 in idea, locally separated from one another, if the space between the impressions 

 is sufficient ; and when they are situated close to one another the mind takes 

 cognizance of their number, and from that and their position determines the size 

 and form of an external object. So is it likewise with the eye, which can per- 

 ceive simultaneously so many objects, and direct the attention at will to each of 

 them as sensible and contiguous points on the retina. The analogy of this 

 power of local discrimination in the impressions of touch and sight with the 

 simultaneous hearing of several tones cannot be doubted, but, while i'or the first 

 the explanation is simple and obvious, an analogous interpretation is not appli- 

 cable to the sense of hearing. In the organs ot touch and sight the severance 

 of the simultaneous impressions rests on the local severance of their external 

 exciting causes ; that is to say, on the excitation, through separate impressions, 

 of different conducting nerve fibres isolated from one another — a point which we 

 had occasion to discuss when treating of the sense of touch. Could it be shown 

 that in the ear likewise the undnlations pertaining to different sounds acted 

 upon different nerve fibres, a severance of impressions, in conformity with the 

 number of single fibres excited, would be a necessary postulate. But no proof 

 of this is possible ; on the contrary, a consideration of the circumstances under 

 which sound is transmitted in the organ of hearing forces us to the conclusion 

 that each wave strikes upon all the nerve fibres, and that a number of undula- 

 tions, originating near one another, must blend in a single movement long before 

 they reach the reservoirs of the nerves. It is clear that the tympanum cannot 

 possibly vibrate at the same time in conformity with the impulse of several un- 

 dulations, slowly with the deep, rapidly with the high pitch, with this and that 

 acceleration, according to the character of the tone, in such wise that the simul- 

 taneous sounds shall be transmitted, without reciprocal disturbance, from the 

 tympanum, through the intermediate organs, to the labyrinth Just as a body 

 on which a blow from different directions simultaneously takes effect, cannot 

 proceed in the direction of both at once, but will take a middle course, so must 

 the vibrations of the tympanum take, according to the laws of mechanics, a 

 middle form, resulting from the different concomitant impulsions ; and hence only 

 a single undulation, as representative and result of all those generated outside, 

 will be transmitted to the labyrinth. Of any contrivance in the labyrinth by 

 which this compovmd movement may be again resolved into its original single 

 elements, and each element — that is to say, each undulation belonging to a de- 

 terminate note or tone — be directed to a special organ, and thus transmitted to 

 the brain, we know nothing and can form no conception. In advance, there- 

 fore, it only remains to suppose that this resultant undulation, as such, strikes 

 on its passage and excites each successive nerve, and that it is the soul which 

 first resolves into its constituent elements the compound sensation arising from 

 without ; but liow, is an inexplicable riddle. 



We leave the consideration of the pure sensations of hearing, and turn lastly 

 to a brief discussion of the ideas derived from this sense and their mode of 

 origination. As with all the rest of the senses, the sensations first acquire value 

 and serviceableness for the intercourse of the soul with the outer world by their 

 association with certain ideas, which, in the previously educated sense, are so 

 unconsciously and infallibly identified with the sensations, that we take them for 

 the sensations themselves. The sensation of hearing, like every other sensation 

 hi sense, is a purely subjective process, a transformation, it might be said, of our 

 consciousness. The cognizance of the existence of an external source of sound 

 as cause of the sensation, the perception of its direction and distance in outer 

 space, pertain to the idea which attaches itself, through a physical' operation, so 

 closely to the sensation, and becomes so blended with it, that we seek not only 



