MUSICAL TONES AND NOISES. 8ll 



The perilymph of the inner ear flows away chiefly through the aqueductus coch- 

 leae, in the circumference of the foramen jungulare, into the peripheral lymphatic 

 system, which also takes up the cerebro-spinal fluid of the subarachnoid space, 

 while a small part drains away to the sub-dural space through the internal auditory 

 meatus. The endolymph flows through the arachnoid sheath of the N. acusticus 

 into the subarachnoid space (C. Hasse). 



414. AUDITORY PERCEPTIONS. Every normal ear is able to distinguish 

 musical tones and noises. Physical experiments prove that tones are produced 

 when a vibrating elastic body executes periodic movements, i.e., when the sound- 

 ing body executes the same movement in equal intervals of time, as the vibrations 

 of a string which has been plucked. A noise is produced by non-periodic move- 

 ments, i.e., when the sounding body executes unequal movements in equal intervals 

 of time. [The non-periodic movements clash together on the ear, and produce dis- 

 sonance, as when we strike the key-board of a piano at random.] This is readily 

 proved by means of the siren. Suppose that there are forty holes in the rotatory 

 disc of this instrument, placed at exactly the same distance from each other on 

 rotating the disc and directing a current of air against it, obviously with every 

 rotation the air will be rarefied and condensed exactly forty times. Every two 

 condensations and rarefactions are separated from each other by an equal interval 

 of time. This arrangement yields a characteristic musical tone or note. If a 

 similar disc with holes perforated in it at unequal distances be used, on air being 

 forced against it, a whirring non-musical noise is produced, because the movements 

 of the sounding body (the condensations and rarefactions of the air) are non-periodic. 

 [The double siren of v. Helmholtz is an improved instrument for showing the same 

 facts.] 

 The normal ear also distinguishes in every tone three distinct factors : 

 [(1) Intensity or force ; (2) Pitch; (3) Quality, timbre or "klang."] 



1. The intensity of a tone depends upon the greater or lesser amplitude of the 

 vibrations of the sounding body. It is well known that a vibrating string emits 

 a feebler sound when its excursions are smaller. (The intensity of a sound corre- 

 sponds to the degree of illumination or brightness in the case of the eye. ) 



2. The pitch depends upon the number of vibrations which occur in a given 

 time [or the length of time occupied by a single vibration]. This is proved by 

 means of the siren. If the rotating disc have a series of forty holes at equal 

 intervals, and another series of eighty equidistant from each other, on blowing a 

 stream of air against the rotating disc we hear two sounds of unequal pitch, one 

 being the octave of the other. (The perception of pitch corresponds to the sensation 

 of colour in the case of the eye.) 



3. The quality or timbre (" Klangfarbe") is peculiar to different sonorous 

 bodies. [It is the peculiarity of a musical tone by which we are enabled to dis- 

 tinguish it as coming from a particular instrument, or from the human voice. 

 Thus, the same note struck on a piano and sounded on a violin differs in quality 

 or timbre.] It depends upon the peculiar form of the vibration, or the form of the 

 wave of the sonorous body. (There is no analagous sensation in the case of light.) 



I. Perception of Pitch. By means of the organ of hearing, we can determine that different 

 tones have a different pitch. In the so-called musical scale, or gamut, this difference is very 

 marked to a normal ear. But in the scale there are again four tones, which, when they are 

 sounded together, cause in a normal ear the sensation of an agreeable sound, which once heard 

 can readily be reproduced. This is the tone of the so-called accord, Triad, or Common Chord, 

 consisting of the 1st, 3rd, and 5th tones of the scale, to which the 8th tone or octave is added. 

 "We have next to determine the pitch of the tones of the chord, and then that of the other 

 tones of the scale. The siren is used for the fundamental experiment, from which the others 

 can easily be calculated. Four concentric circles are drawn upon the rotatory disc of the siren ; 

 the inner circle contains 40 holes, the second 50, the third 60, and the outer 80 all the holes 

 being at equal distances from each other. If the disc be rotated, and air forced against each 



