_What is given in Hearing._--And first, as to the sense of _hearing_. What is it precisely that we hear? When we listen to a sound, we speak of hearing the object that produces the sound; we say, I hear a bell, a bird, a gun, etc. Strictly speaking, we do not hear the object, but only the sound. It is not the bell or the bird that we hear, but the vibration of the air produced by bell and bird. This has been already illustrated by reference to a carriage passing in the street. It is only by experience, aided by other senses, that we learn to refer the sound to its producing cause. _Hearing not properly Perception._--Is hearing then a sensation merely, or is it a perception? If by perception we mean a direct knowledge of the external object--which is the proper sense of the word--hearing certainly is not perception. It gives us no such immediate knowledge. What we perceive in hearing is merely the sensation of sound. It may be doubted whether by this sense alone we should ever get the idea that what we hear is any thing external to ourselves. _Affords the means of Judging._--As it is, however, we judge, not only of the existence and nature, but of the distance and direction of the external object whence the sound proceeds. We learn to do this with great correctness, and with great facility. No sooner do we hear a sound, in most instances, than we form an opinion at once, from what direction it comes, and what produces it; nor are we often mistaken in our judgment. The faculty of judging by the ear as to the direction of the sound, and the nature of the object producing it, may be cultivated by care and practice to a remarkable degree of accuracy. Napoleon was seldom mistaken as to the direction and distance of a cannonade. It is said that the Indian of the north-western prairies by applying his ear to the ground, will detect the approach of a body of cavalry at a distance beyond the reach of vision, and distinguish their tread from that of a herd of buffaloes. _Number of Sounds._--The number of sounds which the ear can distinguish is almost without limit. There are, it is said, five hundred distinct tones which an ear of usual accuracy can recognize, and each of these tones admits of five hundred variations of loudness, giving, in all, two hundred and fifty thousand different sounds.