The atmosphere is the more appropriate vehicle for the communication of sound, though liquids and solid bodies answer the same purpose.

FIGURE IV. -THE EAR.

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A MAP OF THE EAR. 1 The external auditory tube. 2 The membrane of the tympanum. 3 The Eustachian tube. 4 The hammer. 5 The anvil. 6 The round bone. 7 The stirrup. 8 The oval opening. 9 The semicircular canals. 10 The vestibule. 11 The cochlea.

The essential part of the organ of hearing is the soft pulp of the auditory nerve, floating in the midst of a gelatinous fluid contained in the cavities of the internal

ear.

The function of this organ is to produce an impression of sound. But the harmony and melody of sounds is perceived by internal cerebral organs. It is sufficiently apparent that the power of distinguishing melody is not determined by the perfection of the organ of hearing

alone; for many hear very acutely, and are insensible to music. Among birds, the female hears as well as the male, but cannot sing. Some men sing very well, who hear very indifferently. But the same persons would make better music were their power of hearing perfect. Hence the power of distinguishing musical sounds depends on the organ of hearing and the cerebral organ conjointly.

SENSE OF SIGHT.

The eyes, the organs of this sense, are placed in two cavities of the scull, known by the name of orbits. The eye-brows, eye-lids, and the lachrymal apparatus are mere appendages of the organ.

opening in the cenIt is the color of the All the light

The eye is composed of three humors, which are covered by appropriate membranes. These humors are called the vitreous, (or glassy,) the crystalline, and the aqueous. The first of these constitutes the principal portion of the globe. On its anterior surface is a slight depression, in which is situated the crystalline lens. In front of this is the aqueous humor. In this humor is the iris, which expands or contracts, the tre of which constitutes the pupil. iris that determines the color of the eye. admitted to the eye passes through the pupil. is protected by three coverings. The outer is what is termed the sclerotic. This extends over the whole of the eye except the fore part, which is covered with the cornea. The sclerotic coat is commonly called the white of the eye. These taken together, form a most perfect optical instrument, back of which is placed the retina on which the rays strike, after passing through those changes performed by this instrument.

The eye

It is the retina, (which is an expansion of the optic nerve,) that is affected and put in motion by the rays of light. This motion is transmitted to the cerebral organ by the second pair of nerves, called the optic nerves. These nerves have no function but that of sight. The nerves of sensibility and motion, by which the eye moves and is susceptible of pain, spring from other sources. Tears are secreted by the lachrymal gland, situated within the orbit of the eye at its outer angle, by which the eye is kept moist; and the excess is thence taken up by absorbent vessels in each eye-lid, and thence conveyed into the nose.

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FIGURE V. THE EYE.

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1 The lachrymal gland. 2 Its several ducts, to convey the tears to the eye. 3,3 The puncta. 4, 5 The nasal duct

Its function. It is the function of the eye to receive, modify, and transmit the impressions of light. Internal faculties form conceptions of the figure, color, distance, and other attributes of objects. It is obvious that the degree of perfection, with which the eye will perform its

functions, will depend on its perfect organization and healthy condition. If the cornea or crystalline lens, or the vitreous humor, or all of them be too convex, the rays of light are too soon brought to a focus, and the sight is imperfect. Long sightedness is a defect arising from opposite causes. But if the eyes be perfect, and the brain be defective in those faculties which take notice of the size, form, or color of objects, we shall be unable to distinguish these qualities. Hence our conceptions of objects of sight, and their qualities, will depend upon the perfection of the internal, and the external organs jointly. A careless habit of thinking would lead us to suppose, that the power of distinguishing colors would depend on sight alone; but this is no more the case, than it is that the power of distinguishing sounds depends upon the ear alone.

We now pass from the external senses,

- those curiously organized instruments, to which we are indebted for all we know of the external world, - to the internal cerebral organs, which alone are able to form ideas of existences, their physical qualities and relations.

XXII. - INDIVIDUALITY.

Suppose I saw a man riding over a bridge very briskly. The man, horse, bridge, &c., were painted on the retina of the eye, and the optic nerve carried the impression to the brain, and there a class of faculties, each acting by

means of an appropriate organ, contributed to form the whole scene in my mind.

In the first place, there were several objects presented to the mind, as the bridge, horse, rider, &c. These objects were noticed by the faculty of individuality, whose function it is to notice existences and things, without regard to any of their qualities or relations. It is indeed the function of this faculty to notice every thing which can be contemplated, though it have only an existence in the mind, as justice, virtue, prudence, &c. And the stronger the faculty, the more definite and precise will be the conception. Some have the power so strong, in connexion with other faculties, that they, by aid of marvellousness, personify abstractions, and represent them as active, and as speaking and doing. Poetry is full of such figurative expressions. Thus Gray's celebrated hymn to ADVERSITY.

"Wisdom in sable garb arrayed,

Immersed in rapturous thought profound,

And Melancholy, silent maid,

With leaden eye, that loves the ground,

Still on thy solemn steps attend;

Warm Charity, the general friend,

With Justice, to herself severe;

And Pity, dropping soft the sadly pleasing tear."

The organ, and its location. Those persons who are remarkable for their observation of things, and have an aptitude for acquiring a knowledge of details and of individuals, have usually great breadth between the eyebrows, or a prominence immediately above the top of the nose. When large, the forehead seems to point down between the eye-brows. It was large in Dr. Spurzheim,