Page images
PDF
EPUB

rity, in the form of colourless rock-crystal or crystals of 6 to 16: so that, supposing the acid to be a comof quartz. By heating these substances redhot, and pound of two equivalents of oxygen, the number for throwing them into water, they may be disintegrated boron will be 6, and that for the acid 22. Boracick and reduced to fine powder by pounding. Sufficient- acid may be obtained by dissolving a given weight ly pure silex may also be obtained by calcining com- of a salt called borax (which is imported from India mon flints at a low red heat. They may then be easily in a rough state under the name of tincal) in boiling reduced to powder. In this state they must be mix- water; and adding half its weight of sulphurick acid, ed with four times their weight of carbonate of pot-previously diluted with an equal quantity of water. ash, and fused in a crucible, by a strong red heat. Upon evaporation of the solution and cooling, shiA strong effervescence will take place; after which ning, scaly crystals will be precipitated, which is the heat must be urged till the materials enter into the substance in question. It is also found native in complete and quiet fusion. The compound may be the neighbourhood of volcanoes. dissolved, when cold, in water; and the alkaline solution, after filtration, dropped gradually into diluted sulphurick or muriatick acid. An abundant precipitate will subside, which, after pouring off the liquid which covers it, must be thoroughly washed till the water comes away perfectly tasteless: it must then be dried.

Silex thus obtained is a perfectly white and tasteless powder, which feels harsh between the fingers. Its specifick gravity is 2.6. It is insoluble in water, and is not acted upon by any acid except the fluorick, whose properties will be hereafter described. When first prepared, and minutely divided, it is taken up by solutions of pure potash or soda, but not by the volatile alkali ammonia.

Silex, in combination with the fixed alkalis, forms the basis of that inestimable product of art, glass. When one part of very pure sand is ignited with three of carbonate of potash, a compound is formed, which is very soluble, and deliquesces (attracts moisture) in the air. When these proportions are reversed, and three parts of sand and one of carbonate of potash are fused together, the product is insoluble in water and all the acids except the fluorick, and possesses the well-known properties of glass. Its purity depends upon the purity of the ingredients employed in its manufacture. Green bottle-glass is made of impure materials; such as sand, which contains a considerable proportion of iron, and the commonest kind of soda called kelp. Window-glass is made of pure alkali, and sand which is free from iron; and for plate-glass the utmost care is taken to provide both the materials in their purest forms.

BORON.

When equal parts of the metal potassium, and very pure boracick acid, are heated together in a copper tube, at a temperature of about 302° Fahrenheit, they suddenly become redhot: the metal disappears, and, when the product has been washed with warm water, a greenish-brown or olive-coloured substance is obtained, which is boron.

It is destitute of smell, and possesses very little taste. It is sparingly soluble in water, and the solution reddens vegetable blue colours; and what is very singular, it also reddens the yellow colour of turmerick in the manner of alkalis. It is soluble in alcohol, and communicates a beautiful green colour to its flame. It fuses when heated, and gives off its water of crystallization to the amount of about 44 parts in the hundred. It is therefore probable that the crystallized acid is composed of 1 equivalent acid 2 ditto of water

THE FIVE SENSES.

THE SENSE OF SIGHT.-No. V.
DEFENCES OF THE EYE.

22

18

40

The "loving kindness" of the Creator is beautifully exhibited in the provisions he has made for the preservation of life amidst the multifarious dangers which hourly threaten it with extinction. To notice only a few of the more obvious instances, as they float on the surface of his oceanick wisdom, we may hold to admiration the well-compacted strength, up the wind-like fleetness, and the ready sagacity, which combine to give the lion the supremacy, alike of forests, deserts, and cultivated plains. An impenetrable shell saves the torpid and slow-going tortoise from the crush of the elephant's foot; and, in the hour of need, an armature of spines, like threatening spears, couching in every direction, preserve by intimidation, the weak and unoffending hedgehog from a host of powerful assailants. Upon our heaths the furze-bush stands as a fortress to the gentle linnet against the pursuit of the rapacious hawk; and, in tropick lands, the pendant nests of the loxia and Baltimore birds swing from the end of graceful boughs, like the bunches of sour grapes in the fable, to set on edge the teeth of the wily serpent, who would fain destroy the tender broods, but dares not trust his weight to the fragile branches. In our retired streets, when a family of loquacious sparrows squat down to discuss their roadside morsels, a lonely fellow, chosen from the party, sits high up on the corner of some adjacent spout, as a sentinel, to warn them of a coming stone or an advancing cat; and when Boracick Acid. There is considerable discrepance the plenitude of summer flowers, and the insects in the results or experiments upon the quantity of oxy- which make each opening bud a nation, are exhaustgen which is absorbed by boron during its combustion; ed ;-when the harvest-fields cease to yield their inbut there is reason to think that 100 grains condense crease, and the gray mists of coming winter clothe 266.6 grains of that gas which is in the proportion the autumnal eves with sadness, then millions of the

It is insoluble in water, tasteless, and does not effect the colour of blue vegetables. It may be exposed to the strongest heat in close vessels without undergoing any change: but when heated to about 600° Fahrenheit in the open air, it burns vividly, absorbs oxygen, and is converted into boracick acid. It is a non-conductor of electricity.

BORON AND OXYGEN.

feathered tribes, borne on strong aerial wings, cross | effected by a curtain-like membrane, called the tuniseas and deserts to seek afar off a warmer sun and ca conjunctiva.

richer lands. Innumerable genera of beetles-" the creeping things of the earth,"-covered with thick plates of shelly armour, return hollow sounds, instead of sweet morsels, to the eager bills of hungry birds. One of these "armed knights," called the bombardier, puffs at his enemies a cloud of poisonous smoke, and walks quietly away in the very face of half-suffocated foes. But to make an end of examples which are infinite in number as they are infinite in wisdom, we shall only notice the cuttle-fish, which in the eyes of ignorance, would appear to be a very helpless creature, but is, in reality, as well defended as a king by loyal subjects. This inhabitant of the waters, the moment he is menaced by any danger, discharges a quantity of intensely black fluid, in the centre of which he rests, and by which he becomes suddenly invisible. This fluid forms the basis of Chinese, or, as it is more commonly called, Indian ink.

The conservative providences of God are, however, no less evidenced in the preservation of particular organs, and little and apparently insignificant parts of animals: thus, the heart is preserved from rupture by the great strength of its twisted fibres, and from external injury by the breast-bone and ribs; the bowels from corrosion by a soft covering of mucus; the teeth from too rapid wear, by their enamel; and the eye from a multitude of distressing evils, by various admirable contrivances,

which it will now be our business to describe.

[graphic]
[blocks in formation]

The first defence of the eye consists in its lodgement within the walls of a strong bony chamber, called the orbit. This cavity is composed wholly and in part of seven curvilinear bones, severally called os frontis, os sphenoidale, os ethmoides, os maxillare, os male, os unguis, and os palati.

The edge or rim of the cavity is formed by the os frontis, os maxillare, and os male; and the rest of the bones contribute to form the bottom and sides. The bottom is perforated by the foramen opticum, an angular hole, to give passage to the optick and other nerves, blood vessels, &c. The whole chamber is lined by a continuation of the dura mater, a membrane which protects the brain.

The two orbits, in their natural positions, might be compared to two funnels, placed horizontally, side by side, opening with their mouths outwards. In these fastnesses the eyeballs are most effectually preserved from external violence. Concussions are dispersed in the joinings of the bones, which, had the orbit been formed of a single piece, instead of seven, might have often suffered fracture from their influence. The situation of the orbits in contributing to the safety of the eyes is also most "express and admirable;" for, be it observed, they stand centrally between the projections of the nose, brow, and cheek bones, which, in cases of a fall or a blow,

receive the entire shock.

2. THE CURTAINS OF THE EYE.

It is necessary that the interiour of the socket of the eye should be guarded from the intrusion of dust or other extraneous matters. This is ingeniously

Section of the eye, showing its situation in the orbit. This membrane, which is also called the adnata, is an infected prolongation of the skin of the eyelids. Before, however, we proceed to describe it, the reader will please to examine closely the following diagram, by which he will acquire a clearer idea than words can convey of its form and situation, and, consequently, be better able to understand the remarks that follow. Let a represent the eyeball, and bb the upper and lower lids. Now it is plainly manifest

[subsumed][merged small][graphic][subsumed]

that some additional contrivance is wanting to prevent dust or other bodies working their way through passages at c c, between the ball and the lid, into the socket of the eye, where their presence would excite insufferable and incurable pains. To meet this exigency, we find that the common skin of the eyelids d d, after covering their respective edges, goes inwards a little way between the lid and the ball, and then turning backwards, is reflected over the surface of the cornea, where, to prevent the ohstruction of vision that would otherwise follow, it becomes perfectly transparent. We think that no part of our marvellous bodies exhibits a more pleasing instance of the economy, wisdom, and tenderness of the Creator. The economy of this arrangement is evidenced in the circumstance of no new organ having been created for the purpose-it is an adaption of the skin of the eyelids. Its wisdom is shown in the simplicity of its design, in the merring truth

with which its functions are performed, and in the singular circumstance that the difficulty of the case had to be overcome by one of greater magnitudethat of passing the skin of the eyebrows across the very pupil. But God, whose "understanding is infinite," with a majesty which is heightened rather than diminished by the littleness of the objects, steers the course between pain, on the one hand, and blindness on the other, by making the membrane, where it covers the pupil, "transparent." And the tenderness of his care is shown in the fact, that without this little but difficult contrivance, we could not long have used our eyes; but with it we can live our threescore years and ten without annoyance, even from the smoke and dust of the city.

3. THE EYELIDS.

These are composed of the common integuments, with a cartilaginous margin to give them shape, and muscular fibres to give them motion. The cartilage which forms the margin of the lids is called the tarsus, and, like all the parts of the eye, is an exquisite piece of mechanism. It lies like a hoop on their edges, and, from its stiffness, keeps them of a circular figure, so that they close neatly over the eye, and meet with the most perfect accuracy.

The upper eyelid only is moved for the admission of light to the eye; it is raised, or in common language," the eye is opened," by a muscle called the levator palpebra. In "shutting the eye," the closure of the lids is effected by a muscle called orbicularis palpebrarum, which acts with great power on both eyelids.

[merged small][graphic]

66

The eyelids separated, and viewed from behind; a, the lachrymal gland; 6, the ducts from ditto; c, the mouths of these ducts; d, the puncta lachrymalia: e, the meibomean glands, described in Section 3. 2. the contrivance by which particles of dust, &c. are kept from the inner chamber of the eye; but we have now to explain the use of tears in cleansing the surface of the eyeball, from similar impurities. When motes rest upon the eyeball, they are, by winking," immediately wiped off into the channel of the lower lid, when the exquisite sensibility of the membrane by which it is lined, excites the lachrymal gland to a copious discharge of tear water; the eye is suffused, and the offending atoms floated to the inner angle of the lids, and discharged. But here the remedy threatens to become a disease, and an apImmediately within the edges of the eyelids, be- paratus is wanted for draining off the superfluous neath the surface, a number of beautiful little glands water, which, if it were left, would dazzle the sight, are embedded, called the meibomean glands, and from inflame the lids, and cause the lashes to rot at their these, about twenty or thirty ducts, or pipes, open roots, and fall. This would at once have made upon the edge of each eyelid. In the glands a white man a miserable creature, and therefore God, who, greasy matter is secreted from the blood, and slow-as Paley remarks, has made no organ to irritate or ly poured by the ducts upon the edge of the lids, give pain, but all for pleasure and convenience, has, which they defend from being inflamed by the tears, in this instance, made a beautiful provision for the and assist also in striking them together during defence of the eye in the creation of

sleep. It is this matter in a dried state which we 6. THE PUNCTA LACHRYMALIA, AND THE LACHRYMAL pick from the inner corners of the eyes, on arising

in the morning.

Upon the outer edge of the eyelids, fringes of hairs called the lashes, defend the eye from insects, and are of constant use in mitigating the "too fierce impression" of the sun's light.

4. THE SECRETION AND DISTRIBUTION OF TEARS.

Tears, which equally express our joys, sorrows, pity, and affections, flow more constantly than we are accustomed to consider. Like spoiled children we may literally be said to be "always crying;" for, whether asleep or awake, the brilliant tears pursue their crystal course in a perpetual stream over the eyeball, moistening its surface, and washing away its impurities. This, as a defensive provision, is that which we have now chiefly to consider.

5. THE LACHRYMAL GLAND.

SACK AND DUCT.

[graphic]

The eyelids viewed from before; a, the canalicula lachrymates, b the lachrymal sack.

The puncta lachrymalia are two small holes, placed at the inner angle of the eyelids, forming the mouths of a double canal (canalicula lachrymates) or duct for draining off the tears from the eye into the nose.

The lachrymal gland is a small spongy body, of a flattened form, seated in the hollow of the bone in the upper and outer part of the orbit, just beneath the outer end of the brow. Its office is to secrete the fluid of the tears from the blood, and to discharge The lachrymal sack is a bag of an oval shape, fixed it over the surface of the eyeball. This it performs by to the end of the double canal, and lies in a depresVOL III.-42

sion of the nose bones. It terminates in a tube, called the duct, which passes through a hole made for it in the nose-bones, and opens into the nostril. The manner in which this apparatus acts, is as follows-Tear-water, on its discharge from the lachrymal gland, at the upper and outer part of the front of the eyeball, descends by gravity, and is continually spread in greater or less quantities over its face, washing away impurities, and preserving its brilliancy; it is then collected in the inner angle of the eye, and absorbed by capillary attraction into the puncta lachrymalia, the tube from which immediately discharge it into the lachrymal bag and duct, which, together, act like a syphon, and empty it into the nostril, where the constant passage of warm air causes its speedy evaporation.

We have only now to notice, in connexion with the tears, a contrivance of great beauty for ensuring their discharge during sleep, when the lids closely embrace the eyeball. In our description of the structure of the lids, we mentioned that their edges were kept of their proper circular form by a cartilaginous hoop, called the tarsus. Now it is found, on a closure of the lids, that the edges of the tarsus incline inwards, so that the lids touch each other only on the front edges, and leave behind them a triangular gutter thus:-in which the tears run as smoothly as water in a conduit-pipe, to the puncta lachramalia. Without this assistance," nature's sweet restorer, balmy sleep," could only have been enjoyed with the daily penalty of sore eyes. Can anything speak more strongly of HIM who has said, "that his goodness is over all his creatures ?"

7. THE EYERROWS.

The last defence which we shall notice is the brow. Man, the child of disobedience, daily suffers urder a judgment in which, however, much of mercy mingles. He is the victim of fatigue, and in the sweat of his brow he eats his bread. When labour exhausts and inflames the system, the forehead and temples usually perspire in great quantities, and on such occasions the eyes would have been in danger of irritation from the entrance of the "briny drops," had not the brows stood, as they do, immediately over them. The perspiration is caught in its descent, and held among the hairs of the brows, till it either evaporates, or is wiped away. Persons used to a town residence, or a temperate climate, can hardly conceive how useful the brows are in this respect, to the husbandman and the slave.

ash leaves, for the purpose of securing themselves against the bite of the rattlesnake; and it is said that no person was ever bitten who had resorted to this precaution.

The accounts given by Judge Woodruff mention that he was one of a small party who went to the Mahoning river for the purpose of hunting deer. The party took their station on an elevated spot fifteen or twenty yards from the water's edge. Here the men watched for their wished-for game about an hour; but instead of a harmless and beautiful deer, they saw a large rattlesnake which had crawled out from among the rocks beneath them, and was slowly making his way across a narrow smooth sand beach towards the river. Upon hearing the voices of the men, the snake halted and lay stretched out with his head near the water. It was now determined to try the white-ash leaves. Accordingly search was made, and a small white-ash sappling, eight or ten feet long, was procured, and with a view to make the experiment more satisfactory, another sappling of sugar-maple was cut. In order to prevent the snake's retreat to his den, the judge approached him in the rear, and when he had advanced within almost eight feet of him, the snake coiled up his body, elevated his head several inches, brandishing his tongue, and thus signified his readiness for battle.

The judge then presented his white-ash wand, placing the leaves upon the body of the snake. The snake instantly dropped his head upon the ground, unfolded his coil, rolled over on his back, twitched and twisted his whole body in every form but that of a coil, and gave signs of being in great agony. The white-ash was then laid by, upon which the snake immediately placed himself in a coil, and assumed the attitude of defence as before. The sugar maple stick was next used. The snake darted forward in a twinkling, thrust his head into the leaves "with all the malice of the under fiends," and the next moment coiled and lanced again, darting his whole length with the swiftness of an arrow. "After repeating this several times," says the judge, "I changed his fare, and presented him with the white-ash. immediately doused his peak, stretched himself on his back, and writhed his body in the same manner as on the first application. It was then proposed to try what effect might be produced upon his temper and courage by a little flogging with the whiteash. This was administered; but instead of rousing him to resentment, proved only to increase his troubles. As the flogging grew more severe, the snake frequently stuck his head into the sand as far as he could thrust it, seemed desirous to bore his way into the earth, and rid himself of his unwelcome

ANTIPATHY OF THE RATTLESNAKE TO WHITE-ASH. visiters. Being now convinced that the experiment

A writer in Silliman's Scientifick Journal gives an account of an interesting experiment made upon the body of a large rattlesnake, a few years since, in the northern part of the state of Ohio. The experiment which we are about to relate was made about thirty years ago by Judge Woodruff, in order to test the accuracy of a prevailing notion among the people, that the leaves of the white-ash were highly offensive to the rattlesnake, and that this horrible reptile was never found on land where the white-ash grows. It is the uniform practice among the hunters who traverse forests in the summer, to stuff their boots and shoes and pockets with white

was a satisfactory one, and fairly conducted on both sides, we deemed it ungenerous to take his life after he had contributed so much to gratify our curiosity, and so took our leave of the rattlesnake, with feelings at least as friendly as those with which was commenced our acquaintance with him, and left him to return at leisure to his den.”

Evils in the journey of life, are like the hills which alarm travellers upon their road; they both appear great at a distance, but when we approach them we find that they are far less insurmountable than we had conceived.

[merged small][graphic][merged small]

a quantity of air; but being let out, they shrink, become flaccid, and the animal again appears lean and cadaverous. The head is immoveable, except as it turns with the body; but to recompense for that defect, it possesses fine eyes, about the size of a pea, which it can move in a peculiar manner, with different motions, the one backwards, the other forwards one upwards, the other downwards; or fix one of them on any object, while the other moves in pursuit of some other so that its eyes are quite independent of each other, and capable of all the evolutions that can be imagined. The eye is formed with concentrick circles, one within another, the innermost having an aperture about as large as the head of a pin, through which the light enters, and effects the power of vision. The animal does not appear to have any ears, but it has two small openings in the head, which serve for nostrils.

The chameleon is an animal of the lizard species, | small veins, and therefore capable of expansion by about which so many stories have been told, and so much curiosity excited, that no apology need to be offered for the description here given. It is a native of various countries, particularly in the warm climates; and many of them are found about Smyrna, and other parts of Turkey. Its head is larger than the common lizard; and its back is shaped very similar to that of a pig. It has four feet, which are divided into claws resembling those of a parrot; and it has a long flattish tail, of which it makes great use in climbing, for thereby it will hang to the branches of a tree, as well as by its feet, and draw up its body to a resting place. Its tongue is three or four inches long, of a whitish grisly substance, round as far as the tip, which is hollow, and shaped like the end of a pestle, somewhat like the proboscis of an elephant. The tongue is contained in a sort of sheath, joined to the throat, from which the animal can dart it with extraordinary quickness upon flies that come in its way, or other small insects, on which it undoubtedly feeds, and not on the air, as some fictitious romances have stated. In order to retain those flies, the tongue of the chameleon is supplied from its throat with a viscous or glutinous matter, which exudes from the tip, and secures the victim, which it then draws into its mouth. However, these animals can live a long time without taking any visible sustenance, and from this circumstance has probably risen the errour of supposing that they live on the air alone: the fact is, that the lungs of the chameleon, reaching almost the whole length of its body, are so formed that it can draw in so much air as from a thin and lank appearance to seem full and gross. Its lungs are divided into two lobes, placed on each side of its body: they are of a thin membraneous substance, full of

The most astonishing quality of the chameleon is the faculty of changing its colour, and assuming those of the objects near which it is placed. The usual colour of those observed about Smyrna is green, darker on the back, and lighter beneath, inclining to yellow, with spots sometimes reddish, sometimes whitish. There are many of them to be seen among stones, and on the earth, of a grayish colour, like the stones and moss among which they breed; but on being handled, or removed to other places, they have not always appeared to take the colour of that upon which they have been placed; and naturalists differ in their opinions, as to the reason or manner of the chameleon's changing its colours. Some maintain it is done by suffusion, others by reflection; and some think it is by the different disposition of the skin, which gives a modification to the rays of light.

« PreviousContinue »