NATURAL HISTORY. 



" Life speeds away 

 From point to point, though seeming to stand still." Yocxo. 



course, the tremulation excited in them by the motion of the air 

 are comparatively weak. Young children accordingly are extremely 

 fond of noise. It arouses their attention, and conveys to them the 

 agreeable sensation of mind ; but feeble sounds are not perceived, 

 which gives infants, like deaf persons, the appearance of dullness 

 or want of intelligence. 



146. Why are we compelled to use both ears in order to 

 determine the direction of a sound ? 



Because every sound comes more directly to one ear than to 

 the other, and it is only by comparing the intensity of the two 

 impressions, that we are capable of deciding whence the sound 

 proceeds, 



147. If we close one ear perfectly, and cause a slight noise to be made in a 

 dark place at a short distance, it would often be impossible to determine its direc- 

 tion ; in using both ears this could be determined. If a person wakes in the night and 

 hears a sound but cannot tell from what quarter it proceeds, he will turn his face 

 full in the direction from which he supposes the sound to come, thus availing 

 himself of both ears ; having determined this, and wishing to distinguish the sound, 

 he will incline one ear only for this purpose. 



148. Why do persons ivho are partially deaf place their hand 

 behind the ear, in order to hear more distinctly? 



Because the hand thus placed acts upon the same principle as the 

 sounding board ; that is to say, the sound reverberates against it, 

 and penetrates the ear, instead of passing by, which it would do, if 

 no barrier existed. 



149. Why will a person who is partially deaf frequently hear 

 more distinctly when addressed in a moderate tone, than when called 

 to in a loud voice ? 



Because in many cases of defective hearing, the impaired organs 

 are so extremely sensitive, that a loud voice acts like a concussion 

 upon them, and thus defeats its own end ; whereas a moderate 

 tone adapts itself to the limited power of hearing, and thus 

 makes a suitable impression. 



