UNCERTAINTY OP SOUNDS. 70 



body, and that it is propagated through the air, so that 

 what we immediately hear is really the air, and not 

 the body the motion of which first originates the 

 sound. It also goes in the direction opposite to that 

 of the motion by which it is originally produced ; and 

 against the motion of the air which is the medium 

 of it, though that motion both retards its progress 

 and diminishes its loudness, yet not to the same ex- 

 tent as the motion of the air. The wind renders 

 sound less audible ; but the audibility is diminished 

 in the direction of the wind as well as in the opposite 

 direction, though not quite to the same extent. 

 When a coach is on the road, and not in sight, we 

 can hardly tell whether it is before us or behind ; and 

 if there be any thing near us that will echo the sound, 

 the sounding body may appear to be sometimes on 

 one side of us, and sometimes on another. The 

 swelling and sinking of the'sound are the only means 

 that we have of ascertaining whether it is coming 

 nearer to us or going farther away ; and there are 

 many circumstances by which we may be deceived 

 even then. A clump of trees, or any other object 

 that can deaden the sound, will make us think that 

 which is actually approaching us is retiring ; and the 

 clearing of such an obstacle will make that which 

 in reality is approaching be heard as if it were going 

 away. Thus the ear has, in itself, no more power 

 of enabling us to discover that the voice which we 

 hear in nature is the true voice, than it has of letting 

 us know that what our fellow-men tell us is the truth. 

 It is principally on account of this want of con- 

 nexion between the hearing of sounds, and know- 

 ledge of the nature, or even the existence of the 

 sounding body, that we are more startled by sudden, 

 loud, and unusual sounds than by any other sudden 

 and strong affection of the senses. In the discharging 

 of firearms, it is the report which frightens both men 

 and animals, and not the bullet, though the report is 

 perfectly innocent, and the bullet carries wounds and 



