, other things being
equal, depends upon the size of the ear. In timid animals, as the hare
and the rabbit, the ear is very large. They are thus apprized of the
approach of an enemy in time to flee to a place of safety.

The ear-trumpet--which is a tube wide at one end, where the sound
enters, and narrow at the other, where the ear is applied--is
constructed on this principle, its sides being so curved that, according
to the law of reflection, all the sound which enters it is brought to a
focus in the narrow end. It thus increases many fold the intensity of a
sound which reaches the ear through it, and enables a person who has
become deaf to common conversation to mix again with pleasure in
society. The concave hand held behind the ear answers in some degree the
purpose of an ear-trumpet.

_The Ear of Dionysius_, in the dungeons of Syracuse, was a notorious
instance of a sound-collecting surface. The roof of the prison was so
formed as to collect the words, and even whispers, of the unhappy
prisoners, and to direct them along a hidden conduit to where the tyrant
sat listening.

Acuteness of hearing requires the healthy action of the brain, and
particularly of that portion of it from which the auditory nerve
proceeds, combined with perfection in the structure and functions of the
different parts of the ear. The best method, then, of retaining and
improving the hearing, is to observe well the general laws of health,
and particularly to avoid every thing that will in the least impair the
structure or healthy action of the parts immediately concerned in the
exercise of this function. Inflammatory fevers, affections of the brain,
and injuries upon the head, are among the more common causes of
imperfect hearing. Hence the impropriety of striking children upon the
head in correcting them, whether in the family or in the school. The
instances are not few in which deafness, and the impairing of the mental
faculties, have resulted from that barbarous practice familiarly known
as "boxing the ears." This inhuman practice is likely to result in
injury to the drum of the ear, either in thickening this membrane, or in
diminishing its vibratory character. Inflammation of the ear-drum,
either acute or chronic, is the common cause of its increased thickness.
How often this is produced by blows, the reader may judge. Diminution of
the vibratory character of the ear-drum may result from an accumulation
of wax upon its outer surface. In