Manner in which Sound is produced. 207 



which communicates to the sensorium the sound brouglit 

 out of the confined portion of air. How this is effected we 

 do not know, any more than how the internal apparatus, con- 

 nected with the other senses, act in conveying impressions 

 to the mind. 



This theory, derived from the intervention of the tympa- 

 num, implies that what we hear, is not the actual sound 

 evolved at the spot where the first collapse takes place, when 

 we are at a distance from it, but only that which is produced 

 from the air in the internal ear, when it has received impulse. 

 This last is modified by external influence, so that the per- 

 ceptions of distance, intensity, and quality, are conveyed. 

 If any difficulty should appear to rest on this part of the sub- 

 ject, it will be found equally to rest on the common theory. 



With reference to the transmission of sound through solids, 

 I do not suppose there is any such thing ; but that motion 

 only, or perhaps more strictly speaking, impulse, is trans- 

 mitted. When a blow is struck on the end of a long mass of 

 iron at rest, air is displaced, the vacuum filled, and sound 

 produced at the spot where the blow is given. The impulse 

 of the blow is transmitted to the other end, and there affects 

 the air, communicating impulse, and thus causing sound to 

 be produced. In the case of bodies of little density, such as 

 a log of wood, there being air in its cells aud tubes, sound is 

 produced as the impulse advances ; but the sound heard when 

 tlie ear is placed in contact, or nearly in contact, with the 

 farther end, is only the sound produced by the transmitted 

 impulse on the internal ear, which requires but little force to 

 effect the nervous expansion. The cause of the motion of 

 the air preserving its intensity in its passage through a tube, 

 is simply that radiation and dispersion are prevented to a great 

 extent ; and retardation by reflections is greatly reduced by 

 smoothness and elasticity of the interior surface. When air, 

 in the condition of giving out sound, impinges on an inelas- 

 tic surface, the motion is not reflected at all. An organ pipe 

 lined with flannel gives no sound. 



There are many facts connected with sound which remain 

 to be investigated, in reference to the mode of its production, 

 and the influence upon it of the foi*ms and substances of mu- 



