he shutting of a knife, the dropping of various coins, the moving of
different articles of furniture, etc. It may also find appropriate
exercise in determining the direction from which various sounds proceed;
in recognizing acquaintances by their natural voices, and in detecting
the counterfeit voices of companions; in arranging and classifying the
elementary sounds of the language, and in determining all the different
musical tones; in judging of the genus and species of birds by their
chirping, of the distance and nature of sonorous bodies of various
kinds, etc., etc. These are some of the direct means of improving this
sense: others will suggest themselves to the thoughtful reader.

THE SENSE OF SIGHT.--The sense of sight, which is the most refined and
admirable of all the senses, still remains to be considered. The senses
generally serve as interpreters between the material universe without
and the spirit within. But it is more especially by the sense of sight
that we are enabled to hold converse with the external world. Without it
we should be deprived of a large portion of the pleasures of life not
only, but even of the means of maintaining our existence. It is through
the sense of vision that the wisdom, power, and benevolence of the Deity
are chiefly manifested to us.

I shall describe the apparatus of vision only so far as is necessary in
order to subserve my leading object, which is the preservation and
improvement of this sense, and the means of rendering it tributary to
intellectual and moral culture. The eye, which is the organ of vision,
is an optical instrument of the most perfect construction. It is
surrounded by _coats_, which contain refracting mediums, called
_humors_. There are three coats, called the _sclerotic_, the _choroid_,
and the _retina_; and three humors, called the _aqueous_, the
_crystalline_, and the _vitreous_.

The _sclerotic_ or outer coat, called also the white of the eye, is an
opaque, fibrous membrane. It has almost the firmness of leather,
possesses little sensibility, and is rarely exposed to inflammation or
other diseases. It invests the eye on every side except the front, and
besides maintaining its globular form and preserving its internal and
delicate structure, serves for the attachment of those muscles which
move this organ. The opening in the fore part of this opaque coat is
filled by the transparent _cornea_, which resembles a watch crystal in
shape, and is received into