It is true that man can accustom himself to nearly all kinds of odor, even to those that at first are very disagreeable. He indeed not unfrequently so vitiates the sense of smell as actually to prefer those scents which, to persons who have preserved the integrity of this sense, are regarded as exceedingly offensive, and even filthy. But why, let me ask, did the Creator give us the sense of smell? Was it to be thus perverted? No, indeed: it was, without doubt, that we might enjoy the refreshing fragrance of flowers and herbs, of food and drink; and also that we might distinguish between air that is pure and healthful, and that which is impure and infectious. As most articles of food which are agreeable to the smell are wholesome, and as those which are disagreeable are generally unwholesome, so, also, those states of the atmosphere which are grateful to this sense are salubrious, and those odors which are pleasant are healthful, while air which is ungrateful will generally be found injurious to health, as will also all those odors which are unpleasant to this sense when in a healthful state. He who has had occasion to enter a crowded court-room, lecture-room, church, or a.s.sembly-room of whatever kind, which has been occupied for a considerable time without adequate ventilation, can not fail to remember the unwelcome impression made upon his nasal organs when first he inhaled the vitiated atmosphere within, though by degrees he might have become accustomed to it, did he remain, so as ultimately to become well-nigh insensible to its noisome influence. But let such and all others be well a.s.sured that, however offensive such a fetid atmosphere may be to the smell, it is equally injurious to the health. And let those who, having returned from a morning walk or healthful exercise in a salubrious atmosphere, have had occasion to revisit the small and unventilated lodging-room in which they spent a restless night without refreshing sleep, perceive, in the sickening smell, a sufficient cause for all their pains and aches, and wonder how they survived such a gross violation of the organic laws.

All of the senses may be improved by education. The sense of smell const.i.tutes no exception to this rule. Let none be discouraged, then; for the more we accustom our lungs and nasal organs to pure air, the more will they require it, and the more readily will they detect the presence of the least impurity.

This sense becomes very acute in deaf persons, and even more so in the case of those that are blind. The reason is obvious; for, as they are led of necessity to rely upon it more than persons who have all the senses, it becomes thereby developed, and is enabled more accurately to judge of the properties of whatever is submitted to its scrutiny. Seeing persons rarely partake of any article of food, and especially of any thing new, without first smelling it, and blind persons never; for this is the only means by which they can judge of its wholesomeness or unwholesomeness without tasting it.

Whatever stupefies the brain, impairs the healthy action of the nerve of smell, or thickens the membrane that lines the nasal cavities, and thus diminishes the sensibility of the nerves ramified upon it, injures this sense. All these effects are produced by the habitual use of snuff, which, when introduced into the nose, diminishes the sensibility of the nerves, and thickens the lining membrane. By its use the air-pa.s.sages through the nostrils sometimes become completely obstructed. It is on this account that most habitual snuff-takers are compelled to open their mouths in order to breathe freely. It has been well said, that if Nature had intended that the nose should be used as a snuff-hole, she would doubtless have put it on the other end up.

THE SENSE OF HEARING.--The external ear, although curiously shaped, is not the most important part of the organ whose function it is to take cognizance of sounds. In the transmission of sound to the brain, the vibrations of the air produced by the sonorous body are collected by the external ear, and conducted through the auditory ca.n.a.l to the drum of the ear, which is so arranged that it may be relaxed or tightened like the head of an ordinary drum. That its motion may be free, the air contained within the drum has free communication with the external air by an open pa.s.sage, called the Eustachian tube, leading to the back of the mouth. This tube is sometimes obstructed by wax, when a degree of deafness ensues. But when the obstruction is removed in the effort of sneezing or otherwise, a crack or sudden noise is generally experienced, accompanied usually with an immediate return of acute hearing.

The ear-drum performs a two-fold office; for while it aids in the transmission of sound from without to the internal ear, it at the same time modifies the intensity of sound. This softening of the sound is effected by the relaxation of a muscle when sounds are so acute as to be painful; but when listening to low sounds, the drum is rendered tense by the contraction of this muscle, and the sounds become, by this means, more audible. The vibrations made on the drum are transmitted by the tympanum--an irregular bony cavity--to the internal ear, which is filled with a watery fluid. In this fluid the filaments of the auditory nerve terminate, which receive and transmit the sound to the brain.

The ear has the power of judging of the direction from which sound comes, as is strikingly exemplified in the fact that when horses or mules march in company at night, those in front direct their ears forward, and those in the rear turn them backward, while those in the center turn them laterally or across, the whole troop seeming to be actuated by a feeling to watch the common safety. This is also ill.u.s.trated by four or six horse teams, and is a fact with which coachmen are familiar. It is further ill.u.s.trated by the dog, and many other animals. The external ear of man is likewise furnished with muscles; and savages are said to have the power of moving or directing their ears at pleasure, like a horse, to catch sounds as they come from different directions; but few men in civilized life retain this power.

The acuteness of this sense in men and animals, 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 acc.u.mulation of wax upon its outer surface. In such cases chronic inflammation of the parts is not unfrequently the result of the injudicious practice of attempting its removal by introducing the heads of pins into the ear.

This wax, it should be known, is designed to subserve an important end; for the tube leading from the external ear, being, like the nose, constantly open, is liable to the entrance of foreign bodies, such as dust, insects, and the like. But, fortunately, it is not left without the means of defense; for on its inside there are numerous fine bristles, which, interlacing each other, interpose a barrier to the entrance of every thing but sound. Moreover, between the roots of these hairs there are numerous little glands, that secrete a nauseous, bitter wax, which, by its offensiveness, either deters insects from entering, or entangles them and prevents their advance in case they do enter. This wax, then, is very serviceable. But its usefulness does not stop here.

When the ear becomes dry from a deficiency of it, the hearing becomes imperfect, as also when it is thin and purulent. This wax not unfrequently becomes hard and obstructs the tube, causing less or more deafness. But this form of deafness may be easily cured, even though it has existed for years; for, having softened the acc.u.mulations of viscid wax by dropping animal oil into the ear, they may be removed by the injection of warm soap-suds, which is an effectual and safe remedy.

The sense of hearing is perhaps as susceptible of cultivation as any of the senses. The Indian in the forest, who is accustomed to listen to the approach of his enemies or of his prey, acquires such acuteness of hearing as to be able to detect sounds that would be inaudible to persons living amid the din of civilized life. The blind, also, who of necessity are led to rely more upon this sense than seeing persons, excel in the acuteness of their hearing. They recognize their acquaintances by the exercise of this sense as readily as persons usually do by that of sight, an attainment which very few seeing persons make, and yet one that is perhaps within the reach of ninety-nine persons in every hundred. The blind judge with great accuracy the distance of persons in conversation, of carriages in motion, and of all sonorous bodies whose vibrations reach their ears. They even estimate with remarkable correctness the distance and height of buildings by the reflection or interception of sound. It is in consequence of the acuteness of this sense, acquired by careful cultivation, that the blind, as a cla.s.s, have become so generally and justly distinguished for their pre-eminence in instrumental music. This enables them also to cultivate vocal music with more than ordinary success.

The due cultivation of the sense of hearing will contribute vastly to promote our intellectual and moral well-being. If it be true, as we are told it is by those who have been engaged in teaching both the deaf and the blind, that the absence of hearing is even a more formidable impediment to the communication of knowledge than that of sight, we must infer that all imperfections of the organ of hearing itself, or in the manner of using it, must correspondingly lessen the accuracy of the knowledge we receive through that organ. The meaning of language very often is conveyed not so much by the words themselves as in the tones of voice in which the words are uttered. If, therefore, the hearing be indistinct, or there be no habit formed of careful attention to the inflections of sound, the impressions received from what we hear must often be inaccurate. Our speech, too, will be far less agreeable, and be inefficient, even if it be not positively inarticulate. We owe it to others, no less than to ourselves, then, to cultivate the powers of the voice--the common instrument that G.o.d has given us for the interchange of thought, sentiment, and feeling, and which, though so common, is the most perfect of all instruments for the transmission of sound. Yet how deplorably is it neglected! how shamefully is it misused! It can be fully developed and made what it is capable of being only through the influence of the ear. If this organ be neglected, the voice must needs be imperfect. And the voices of many persons are through life imperfect and disagreeable, because they were not carefully trained in early life to articulate distinctly, much less to utter _musical_ sounds. The opinion is confidently expressed by those who are best qualified to decide the matter, that nearly all children might be taught to sing, if proper attention were paid early enough to the use they make of their ears and their organs of sound. The careful training of these should be considered an indispensable part of a school-teacher's as well as of a parent's duty.

The ear will find appropriate discipline in distinguishing, without aid from the eye, the causes of various sounds, as the opening of a door, the 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 cla.s.sifying 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 a groove in the front part of the sclerotic coat in the same manner that a watch-gla.s.s is received into its case.

But for this arrangement light could not gain admission to the eye.

The _choroid coat_, which const.i.tutes the second investing membrane of the eye, is of a dark brown color upon its outer surface, and of a deep black within. The internal surface of this membrane secretes a dark substance resembling black paint, upon which the retina is spread out, and which is of great importance in the function of vision, as it seems to absorb the rays of light immediately after they have struck upon the sensible surface of the retina.

The _retina_, which is the third and innermost membrane of the eye, is the expansion of the optic nerve, and const.i.tutes the immediate seat of vision. Such is the arrangement of the humors of the eye, and so perfectly are they adapted to the functions they are called upon to perform, that in the healthy state of this organ, the light entering the pupil is so refracted as to paint upon the retina an exact image of the objects from which it proceeds. The optic nerve, whose expansion forms the retina, receives this image and transmits it to the mind.

Arnott has well remarked, that "a whole printed sheet of a newspaper may be represented on the retina on less surface than that of a finger nail; and yet not only shall every word and letter be separately perceivable, but even any imperfection of a single letter. Or, more wonderful still, when at night an eye is turned up to the blue vault of heaven, there is portrayed on the little concave of the retina the boundless concave of the sky, with every object in its just proportions. There a moon in beautiful miniature may be sailing among her white-edged clouds, and surrounded by a thousand twinkling stars, so that to an animalcule supposed to be within and near the pupil, the retina might appear another starry firmament with all its glory."

Besides these three coats, and the cornea which const.i.tutes about one fifth of the anterior portion of the outer coat, it is necessary to notice the _iris_, so called from its variety of color in different persons, and upon which alone the color of the eye depends. The iris is a circular membrane situated just behind the cornea, and is attached to one of the coats at its circ.u.mference. In its center is a small round hole, called the _pupil_; and sometimes spoken of familiarly as the sight of the eye, as no light can enter the eye except through it. The iris possesses the power of dilating and contracting, so as to admit more or less light, as it may be needed. This change in the size of the pupil is effected by two sets of muscular fibers. The first set converge from the circ.u.mference of the iris to the circular margin of the pupil, and const.i.tute the _radiated muscle_. The outer ends of these fibers are attached to the sclerotic coat, which is unyielding; hence, when they contract, the pupil _enlarges_ to receive more light. The other set is composed of circular fibers, which go round in the iris from the border to the pupil, and const.i.tute the _orbicular muscle_, the contraction of which _diminishes_ the size of the pupil. When too much light enters the eye, the excited and sensitive retina immediately gives warning of the danger, and the nerves, which are plentifully distributed to the iris, stimulate the orbicular muscle to contract, and the radiated one to relax, by which the size of the pupil is lessened. But when the light which enters the pupil is insufficient to transmit a distinct image of objects to the brain, the orbicular muscle relaxes, and the radiated one contracts, so as to enlarge the pupil. The contraction of the pupil is readily seen when a person pa.s.ses from a darkened room into a bright sunlight, or when a light is first brought into a room in the twilight of evening. Any person may notice this contraction in his own eye by beholding himself in a gla.s.s immediately after pa.s.sing from a dark to a well-lighted room. So, also, when a person looks at an object near the eye, the pupil contracts, but when he looks at an object more remote, it dilates. The muscles of the iris are somewhat under the control of the will; for most persons can contract or dilate the pupil, in some degree, at pleasure. Some persons possess this faculty to a great extent.

The three _humors of the eye_ have been compared to the gla.s.ses of a telescope, and the coats to the tube, which keeps them in their places.

The _aqueous_ humor is situated in the fore part of the eye, and is divided by the iris into what are called the anterior and posterior chambers of the eye. The _crystalline_ humor, or lens, is situated immediately behind the aqueous humor, a short distance back of the pupil, and is a perfectly transparent double convex lens, closely resembling in shape the common burning gla.s.s. This resemblance does not stop here; for this lens, like the burning gla.s.s, possesses the property of converging the rays of light which fall upon it, and bringing them to a focus. When this lens becomes so opaque as to obstruct the pa.s.sage of light, either partially or entirely, a person is said to have a _cataract_. This can be cured only by a surgical operation. The _vitreous_ humor, situated back of the other two, forms the princ.i.p.al part of the globe of the eye. It differs from the aqueous in one important particular. When that is discharged in extracting the crystalline lens for cataract or otherwise, it will be restored again in a few hours, and the eye will continue to perform its function. But if this be discharged by accident, the eye is irrecoverably lost. This, however, does not often occur; for, as we shall presently see, the eye is admirably fortified.

The eye is a perfect optical instrument, infinitely surpa.s.sing all specimens of human skill. This is true, view it in what light we may. It not only possesses the power of so adjusting its parts as to adapt it to the examination of objects at different distances, and in light of different degrees of intensity, but we are enabled to direct it at will to objects above, beneath, or around us.

The various motions of the eye are produced by six little muscles. These are attached at one extremity to the immovable bones of the orbit, while at the other extremity they are inserted into the sclerotic coat, four of them near its junction with the cornea, by broad, thin tendons, which give to the white of the eye its pearly appearance. These muscles are so arranged by the matchless skill of the Architect as to enable the beholder to direct the eye to any object he chooses, and to hold it there for any length of time that is compatible with the laws by which muscular exercise should be regulated. By the slight or intense action of four of these, called the straight muscles, the eye is less or more compressed, and the relative positions of its humors are by this means so nicely adjusted as to enable us to view objects near by or at a distance. The other two are called oblique muscles, one of which, with its long tendon pa.s.sing through a cartilaginous loop, acts upon the principle of the fixed pulley, and turns the eye in a direction contrary to its own action. When the external muscle becomes too short, the eye turns out; but if the internal muscle is unduly contracted, the eye turns inward, toward the nose. One eye is sometimes turned up or down, but this is of less frequent occurrence.

It would be interesting to notice the protecting organs of the eye, consisting of the _orbit_, which is a deep bony socket, in which the eye securely rests; of the _eye-brows_, which are two projecting arches, covered with hair, and so arranged as to prevent the moisture that acc.u.mulates upon the forehead, in free perspiration, from flowing into the eye; of the _eye-lids_, which are two movable curtains for the protection of the eye, and which secrete a fluid that moistens and lubricates it; of the _lachrymal gland_, with its ducts, which keeps the eye constantly moist, and whose secretions go on while we wake and when we sleep, etc., etc.; but the preceding must suffice.

With this brief description of the apparatus of vision, we proceed to the consideration of the means of preserving and improving this sense, and of rendering it tributary to intellectual and moral culture.

The rule requiring that _action should alternate with rest_, which has been so often stated, and which applies to all the organs of both body and mind, should be especially observed in relation to the eye. This organ requires exercise, and light is its appropriate stimulus; but injury is the inevitable consequence of keeping it too constantly employed, or too intently fixed for a long time on any object. Whenever the eye is fixed for any length of time upon an object which it distinguishes with difficulty, it experiences a painful sensation, which is a sure indication that it has been overtaxed. The sight is also impaired when the eye is too little used, or when its natural stimulus is shut out, as is strikingly ill.u.s.trated in the case of persons confined in dungeons. A distinguished oculist has said that many men daily impair or destroy their eyes by immoderate use, and that not a few have done the same by too little use of them.

The exposure of the eyes to _sudden transitions from weak to strong light_ is very injurious. This may be regarded as one of the must prolific causes of weakness of sight. The injury is generally gradual, it is true, but it is none the less fatal on that account. The immediate sensation of pain, when a strong light is brought into a dark room, should be a sufficient warning to avoid such sudden extremes. The iris dilates and contracts, and thus enlarges or diminishes the size of the pupil as the light that fails upon the eye is faint or strong; but this dilation and contraction are not instantaneous. There are numerous instances on record in which total blindness has resulted from a sudden transition from darkness to the brilliancy of day. The habit of looking at a bright light of any kind, and especially of watching flashes of lightning, which is practiced by many, is exceedingly dangerous. The practice which many students and others indulge in, of resting their eyes as the twilight of evening advances, and allowing the pupil to dilate until it is quite dark, and then suddenly introducing a bright light, is a palpable violation of this rule, and one that is sure, sooner or later, sensibly to injure the eyes. The exposure of the eyes suddenly to a strong light upon waking from sleep, and all sudden changes of whatever kind from darkness to intense light, should be carefully avoided by persons who would preserve their sight unimpaired.

The strength of light used should be regulated _according to the powers of the eye_. This is a general, though a very important rule. Both the amount and the distribution of light should be such as to produce no unpleasant sensations. The eye possesses a certain degree of adaptation to light, according as it is intense or feeble. Some eyes require a stronger light than others, but all eyes are injured by being used in light that is too intense or too feeble. Reading by a strong sunlight, and by moon or star light, may be adduced as ill.u.s.trations which are alike painful and injurious.

Too little light is well-nigh as injurious as too much, as he can not fail to have noticed who has had occasion to travel a difficult road in a dark night. The injury, in such cases, is two-fold; for while, on the one hand, the radiated muscle of the iris is unduly contracted for a length of time, in order sufficiently to enlarge the pupil to render objects visible, the sensitive retina, on the other hand, is overtaxed to gain a knowledge of them in too feeble light. The pain which the strained eye thus experiences is only an indication and a warning to the individual of the permanent injury he is inflicting upon this delicate organ.

_Rooms should be well and evenly lighted._ The irregular and flickering light of common lamps and candles is very injurious, and should be avoided in the study, and in all mechanical pursuits where the eye is much taxed. The best oculists concur in the opinion that reflected and concentrated light are highly injurious. Several cases of actual blindness are recorded as having occurred within a few years from exposure to concentrated light, and weakness of sight that has unfitted the individual for usefulness through life has often been thus produced.

The rays of the sun are considered as peculiarly injurious when reflected from an opposite building or wall, or even when they pa.s.s through a window, and, descending to the floor, are thence reflected to the eyes. What, then, shall we say of the habit of constructing school-rooms in such a manner that perhaps a majority of the scholars are obliged to write and study at desks upon which the direct rays of the sun shine for a considerable portion of the day unbroken unless it be by a pa.s.sing cloud! And yet thousands of school-houses are situated in such a manner as to create this very necessity all over our country.

At a moderate estimate, the eyes of one hundred thousand children are taxed in this manner in the schools of the United States every pa.s.sing year. A vast amount of discomfort and unhappiness is produced in this way that might easily be avoided, would parents and teachers take the trouble. Any exposure of this kind should be immediately obviated, either by blinds, or by curtains of some soft color. A few newspapers are much better than nothing. The desks and furniture should be of such a color that the eye may repose upon them with agreeable sensations.

Nature is clothed with drapery whose color is refreshing to the eye; and it is false taste, as well as false philosophy, which attempts to dazzle in order to please it.

_The use of side lights is injurious._ The eye will accommodate itself to light of different degrees of intensity within a limited range, but both eyes should be exposed to an equal degree of light. The sympathy between the eyes is so great, that if the pupil of one eye is dilated by being kept in the shade, as must, of course, be the case where the light is on one side, the eye which is exposed can not contract itself sufficiently for protection, and is almost inevitably injured.

When viewing objects, we should avoid, as far as possible, _all oblique positions of the eye_. By neglecting this rule, an unnatural and permanent contraction of the muscle is liable to be produced, as is ill.u.s.trated in the numerous instances of strabismus, or cross-eye, which are every where too common.

_We should accustom the eye to viewing objects at different distances._ The muscles upon which the form of the eye and the size of the pupil depend are subject to the general laws of muscular action. Their strength and flexibility, which are increased by healthful exercise, are impaired by disuse. Hence students who have neglected this rule, and have accustomed themselves for a long time to view objects near by, lose the power of adjusting the eye so as to view things at a distance.

As a consequence, they become near-sighted, and put on gla.s.ses, when, by a proper use of the eye, their vision might have been preserved unimpaired many long years. I know some students upon whom this habit became so firmly fixed before they were twenty years of age, that they felt compelled to put on gla.s.ses, but who, unwilling to contract so pernicious a habit in early life, commenced a course of discipline in accordance with the suggestions here given. By perseverance, their eyes not only recovered their former healthful action, but became so improved that they now possess the sense of vision unimpaired not only, but in a very high state of cultivation.

_Persons become near or long sighted_ as the objects to which they are accustomed to direct the eye are near or remote. This is ill.u.s.trated in the case of students, watch-makers, and engravers, who are accustomed to examine minute objects near the eye, and, as a consequence, become near-sighted; and of surveyors, hunters, and sailors, who, being accustomed to view objects at a distance, become long-sighted. By a proper discipline of the eye, persons may attain and retain the power of viewing objects near by and at a distance, as is ill.u.s.trated in the case of those gunsmiths who are accustomed to manufacture guns, and to try them in shooting at a mark at a great distance. The preceding principles being borne in mind in their various applications. I need, perhaps, state but one more rule.

He who would secure clear and distinct vision, must observe all those rules which are necessary to keep the body in health. The sympathy of the eyes with all the other organs of the body is wonderful and intimate. There is no other organ whose strength depends so much on the general vigor of the system. Strict temperance in eating and drinking may be regarded as an indispensable requisite for the preservation of healthy eyes. To this may be attributed the clear heads of the ancient philosophers, who, unlike most students of the present day, exercised their bodies and limbs as well as their minds. Their works are not the production of congested brains, for these were not oppressed with blood belonging to other parts of the body. They studied and thought, and exercised both body and mind in the open air, and thus observed the laws of health. But among the mult.i.tudes of close students of the present day, who complain of weakness of the eyes, the misfortune is generally attributable to an almost total neglect of the first principles of health.

While we reproach and loathe the man whose eyes are red and weeping with the effects of intemperate drinking, we cordially pity purblind students, as in some sense martyrs to the cause of learning. Dr.

Reynolds, a distinguished American oculist, administers a rebuke to such which we fear is too often merited: "A closer examination of their history presents a very different result. Our sympathy may grow cool if we regard them with a physiologic eye. It is a love of the flesh, more than a love of the spirit, that too often clouds their vision. It is too much food, crowding with unnecessary blood the tender vessels of the retina. It is too little exercise, allowing these acc.u.mulated fluids to settle down into fatal congestion. It is positions wholly at variance with the freedom of the circulation, and various other imprudences, which are the results of carelessness or unjustifiable ignorance. 'The day laborer may eat what he will, provided it is wholesome, and his eyes will not suffer. But let the student, who is called upon to devote not only his eyes, but his brain, to severe labor, live upon highly nutritious food, and such as is difficult of digestion, and we shall soon see how his vision will be impaired, through the vehement and persevering determination of blood to the head, which such a course must inevitably occasion.' So speaks Beer, whose extensive opportunities of observation have perhaps never been exceeded. The daily practice of every observing oculist is filled with coincident experience."

Among the prevalent habits of students by which the eyes are injured, the same writer mentions the irritation produced by rubbing them on awaking in the morning, a practice which has in some cases occasioned permanent and incurable disease; reading while the body is in a rec.u.mbent position; using the eyes too early after the system has been affected with serious disease; exercising them too much in the examination of minute objects; the popular plan of _using green spectacles_, and _the use of tobacco_.

Light which is sufficient for distinct vision, and which falls over the shoulder in an oblique direction, from above, upon the book or study table, is generally regarded, and with great propriety, as best suited to the eyes. Some oculists prefer to have the light fall over the _left_ shoulder.

The acuteness of this sense and the extent of its cultivation are very much greater in some individuals and cla.s.ses of men than in others. This is a fact that has been remarked by observing persons. Its consequences should not be overlooked, for they are neither few nor unimportant.

Those persons who have been long accustomed, either by the necessity of their situation, the example of those about them, or the judicious care of parents and teachers, to observe attentively the relations of parts, the symmetry of forms, or the shades of color, have eyes that are perpetually soliciting their minds to notice some beautiful or grand perceptions. Wherever they turn, they espy some new, and, therefore, curious arrangement of the elements of shape, some striking combination of light and shade, or some delicious peculiarity of coloring. The multiplicity and variety of their perceptions must and do increase the number of their thoughts, or give to their thoughts greater compa.s.s and definiteness. Such persons are likely to become poets, or painters, or sculptors, or architects. At any rate, they will appreciate and enjoy the productions of others who have devoted themselves to these delightful arts. And will not such persons be most readily awakened to descry and adore the power, the skill, and the beneficence of the Great Architect who reared the stupendous fabric of the universe, who devised the infinite variety of forms which diversify creation, and whose pencil has so profusely decked every work with myriads of mingling dyes, resulting all from a few parent colors? To an unpracticed eye, the beauties and wonders of creation are all lost. The surface of the earth is a blank, or, at best, but a confused and misty page. Such an eye pa.s.ses over this scene of things, and makes no communication to the mind that will awaken thought, much less enkindle the spirit of devout adoration, and fill the soul with love to Him "whose universal love smiles every where."

Mr. May speaks no less sensibly than eloquently when he says, "I may be extravagant in my estimation of the importance of the culture of the eye and the ear, but so it is, that while I have been reading the writings of the Hebrew Prophets, and of those other gifted bards who communed so intently with nature and with nature's G.o.d, it has seemed to me impossible that any one could enter fully into all the tenderness, beauty, and sublimity of their language, or receive into his heart all its peculiarity of meaning, unless his own eye had been used to trace the skill of that hand which framed and fashioned every thing that is, and to descry the delicacy of that pencil which has painted all the flowers of the field, nor unless his own ear has learned to perceive the melody and harmony of sounds."

We can discipline the sight directly, and to a very great extent; and we can have the satisfaction of perceiving the progressive improvement of the faculty. For this purpose, every school should be furnished with appropriate apparatus. A set of measures is indispensable. I will ill.u.s.trate by an example. For the benefit of the primary department connected with a seminary of learning that was formerly for several years under my supervision, I constructed a set of rules for linear measurement. Their breadth and thickness were uniform, each being an inch wide and half an inch thick. The set consisted of nine rules, whose lengths were as follows: four were each one foot long; one, a foot and a half long; two, two feet; one, two and a half feet; and one, three feet.

Every rule had a small hole bored through each end. I had also a number of small pins turned just the right size to fit these holes. I have since submitted to several hundred teachers, in inst.i.tutes and elsewhere, my mode of combining and using these measures; and from the deep interest which a large number of intelligent parents and teachers in different localities have manifested in the subject, I venture to refer to it in this connection. I first tried the experiment ten years ago, with a cla.s.s of about twenty children from four to seven years of age. Several of these could not read, and some of them had not learned the alphabet. The children were first led to observe carefully the length of these several rules, until they could determine at sight the length of each. For several of the first lessons some of them would misjudge. They would, for instance, call a two foot rule one and a half or two and a half feet long. In such cases their judgments were immediately corrected by the application of two one foot rules. They were then led to observe with care, tables, desks, etc., and to estimate their length, and were afterward permitted to measure them, and discover the degree of accuracy in their decisions. After obtaining the opinions of the children in relation to the length or height of an object, I would measure it myself in the presence of the cla.s.s. When the cla.s.s became a little experienced, we examined the length, breadth, and height of rooms, of houses, and of churches; and then the distance of objects less or more remote, correcting or confirming their estimates by the application of the rule or measure, which gave a permanent interest to the exercise. By exercising the cla.s.s in this manner, not to exceed half an hour a day, they would, at the end of the first quarter, judge of each other's height, of the height of persons generally, of the length of various objects, of the size of buildings, and of the dimensions of yards, gardens, and fields, with greater accuracy than the average of adult persons, as was tested by actual measurement in some instances where there was a disagreement in opinion.

By holding these rules in different positions, the children readily became familiar with the meaning and practical application of the terms perpendicular, horizontal, and oblique. They would also tell which term is applicable to the different parts of the stove-pipe; to the different parts of the furniture of the school-room; to the floor, sides of the room, roof, etc.; and to all objects with which they were familiar.