Reason Why — Chapter 67

CHAPTER LXVII.

1306. _Whence does the snail obtain its shell?

_ Young snails come from the egg _with a shell upon their backs_.

1307. _How does the shell grow with the increase of size of the animal?

_ The soft slime which is yielded by the body of the animal, _hardens upon the orifice of the shell_, and thus increases its size.

[Illustration: Fig. 80. --COMMON GARDEN SNAIL.

] 1308. _Why is the shell spiral?

_ Partly because of its original formation; but also because, _as the shell grows_, the opening is elongated; and thrown up, causing the spiral body of the shell to turn, and so to wind its growth around the centre.

[Verse: "Notwithstanding they hearkened not unto Moses; but some of them left it until the morning, and it bred worms, and stank: and Moses was wrath with them."

--EXODUS XVI.

] 1309. _Why has the snail four tentacula attached to its head?

_ Because the insect, having no other limbs, is provided with those projecting members, the lower two serving as _feelers_ and the upper two also as _feelers_ and _eyes_.

These, projecting in the front of the animal, impart to it a consciousness of surrounding objects, and especially of those which lie in its path.

1310. _Why is the snail able to move, without feet?

_ Because it has attached to its body a fringe of muscular skin, which is capable of considerable contraction and expansion, and by alternately stretching and shortening this, the snail is able to draw himself along.

1311. _Why do we see no snails in the winter time?

_ Because they bury themselves in the ground, or in holes, where they remain _in a torpid state_ for several months.

Before they enter into the torpid state, they form with their slimy secretion, and with some earthy matters which they collect, a strong cement with which they seal up the opening to their shells.

1312. _Why can snails live in shells thus sealed?

_ Because they leave, in the thin wall by which they close themselves in, _a small hole_, too small to admit water, but large enough to let in sufficient air to carry on their feeble respiration during their winter sleep.

1313. _Why do insects abound in putrid waters, and in decaying substances?

_ Because they have been endowed with appetites and with constitutions that enable them to live upon and to enjoy corrupt matter.

In this point of view the maggots of flies are exceedingly useful; a dead carcass is speedily threaded by them in every direction; thus that corrupt matter which, in a large mass, would poison the air, is taken up in small portions by millions of living bodies, and by them _dispersed_, and becomes innoxious.

[Verse: "For he maketh small the drops of water: they pour down rain according to the vapour thereof."

--JOB XXXV.

] 1314. _Why do we see, in tanks of rain water, insects rising to the surface?

_ Because numerous insects pass through their first stages of existence in _water_, and among them the common gnat.

The gnats of the previous season having deposited their eggs on the sides of the water-butt, the warm water developes them, and the larvæ of the gnats appear (Fig. 81;

_c_ natural size of larva; _b_ larva magnified).

[Illustration: Fig. 81. --LARVA AND PUPA OF GNAT.

(_Greatly magnified.

_)] 1315. _Why do they continually rise to the surface of the water?

_ Because they require to breathe air, and therefore they come up to the surface, where, elevating the tube (_b_) above the surface of the water, they are enabled to breathe.

1316. _Why do some appear to have larger heads than others?

_ Those that have apparently larger heads, and that breathe through tubes attached to their heads (_d_) are in the _pupa_, or second stage of development, and underneath the large shield by which their heads are marked, their wings, feet, &c. , are being formed.

[Verse: "Because thy loving kindness is better than life, my lips shall praise thee."

--PSALM LXIII.

] 1317. _Why, when the water is disturbed, do the larvæ descend more rapidly than the pupæ?

_ Because the pupæ are in a torpid condition, awaiting the formation of their perfect organs.

1318. _Why are the flies able to escape from the water?

_ Because, as their formation becomes perfected, and the fluids of the body of the pupa become absorbed in the production of the light texture of the wings, &c. , _the body and its case become lighter than the water_, and rise and float upon the surface.

The pupa-case then forms a natural boat, from which the fly emerges, and spreading its wings, enters upon the final state of its existence.

[Illustration: Fig. 82. --THE PERFECT GNAT.

ESCAPING FROM THE PUPA-CASE.

_(Greatly magnified.

)_] This interesting metamorphosis may be seen going on in the summer time, in every pond, brook, and reservoir.

A fine sunny morning calls up millions of these little boats from beneath the surface, and the diver within that wonderful little bell breaks its sealed doors, and flies away to enjoy the bright sunshine.

1319. _Why are beetles denominated "coleoptera?"

_ Because they have wings protected by horny sheaths; the term _coleoptera_ signifies _wings in a sheath_.

[Verse: "They shall lie down in the dust; and the worms shall cover them."

--JOB XXI.

] 1320. _Why have beetles hard horny wing-cases?

_ Because they live underground, or in holes excavated in wood, &c. If, therefore, their wings were not protected by a hard and firm covering, they would be constantly _liable to destruction_ from the movement of the insect within hard and rough bodies.

[Illustration: Fig. 83. --STAG-BEETLE, SHOWING ITS WINGS UNFOLDED, AND

THE WING-CASES OPEN.

] The _elytra_, or scaly wings of the genus of scarabæus, or beetle, furnish an example of this kind.

The true wing of the animal is a light, transparent membrane, finer than the finest gauze, and not unlike it.

It is also, when expanded, in proportion to the size of the animal, very large.

In order to protect this delicate structure, and, perhaps, also to preserve it in a due state of suppleness and humidity, a strong, hard case is given to it, in the shape of the horny wing which we call the elytron.

When the animal is at rest, the gauze wings lie folded up under this impenetrable shield.

When the beetle prepares for flying, he raises the integument, and spreads out his thin membrane to the air.

And it cannot be observed without admiration, what a tissue of cordage, _i.

e. _ of muscular tendons, must run in various and complicated, but determinate directions, along this fine surface, in order to enable the animal, either to gather it up into a certain precise form, whenever it desires to place its wings under the shelter which nature hath given to them, or to expand again their folds when wanted for action.

[Verse: "The Lord is good; his mercy is everlasting; and his truth endureth to all generations."

--PSALM C.

] In some insects, the elytra cover the whole body; in others, half;

in others only a small part of it; but in all, they completely hide and cover the true wings.

Also, Many, or most of the beetle species lodge in holes in the earth, environed by hard, rough substances, and have frequently to squeeze their way through narrow passages; in which situation, wings so tender, and so large, could scarcely have escaped injury, without both a firm covering to defend them, and the capacity of folding themselves up under its protection.

1321. _Why have many of the beetle tribe large strong horns?

_ Because, as they live in holes in the earth, or in excavations in wood, they use their horns to _dig out their places of retreat_.

1322. _Why has the giraffe a small head?

_ Because, being set upon the end of a very long neck, the animal would be _unable to raise it_ if it were heavy.

1323. _Why has the giraffe a long neck?

_ Because it _feeds upon the branches of tall trees_.

1324. _Why has the giraffe a long and flexible tongue?

_ Because it is thereby enabled to lay hold of the tender twigs and branches, _and draw them into its mouth_, avoiding the coarser parts of the branches.

1325. _Why are the nostrils of the giraffe small and narrow, and studded with hairs?

_ Because the hairs and the peculiar shape of the nasal passages are designed as a protection against the insects which inhabit the boughs of the trees upon which the giraffe feeds; and also against the sands of the desert, which storms raise into almost suffocating clouds.

* * * * * [Illustration: Fig. 84. --GIRAFFE FEEDING.

] [Verse: "Bless the Lord, all his works, in all places of his dominion: bless the Lord, O my soul."

--PSALM CIII.

] 1326. The distribution of animals, or _Zoological Geography_, is of great interest, and should be carefully studied in connection with _Botanical Geography_ (_see_ 1208).

The highest department of the animal kingdom (writes the Rev. W.

Milner) commences with the class of _Birds_, which may be naturally divided into the three great orders of ærial, terrestrial, and aquatic.

Aggregation into immense flocks is a distinguishing feature of several species, especially of the aquatic order, which form separate colonies, building their nests in the same state, though other spots equally adapted are at no great distance.

Hence the Vogel-bergs, or bird rocks of the northern seas, one of which at Westmannsharn in the Faroe group of islands, seldom intruded upon by man, presents a most extraordinary spectacle to the visitor.

The Vogel-berg lies in a frightful chasm in the precipitous shores of the island, which rise to the height of a thousand feet, only accessible from the sea by a narrow passage.

Here congregate a host of birds.

Thousands of guillemots and auks swim in groups around the boat which conveys man to their domain, look curiously at him, and vanish beneath the water to rise in his immediate neighbourhood.

The black guillemot comes close to the very oars.

The seal stretches his head above the waves, not comprehending what has disturbed the repose of his asylum, while the rapacious skua pursues the puffin and gull.

High in the air the birds seem like bees clustering about the rocks, whilst lower they fly past so close that they might be knocked down with a stick.

But not less strange is the domicile of this colony.

On some low rocks scarcely projecting above the water sit the glossy cormorants, turning their long necks on every side.

Next are the skua gulls, regarded with an anxious eye by the kittiwakes above.

Nest follows nest in crowded rows along the whole breadth of the rock, and nothing is visible but the heads of the mothers and the white rocks between.

A little higher on the narrow shelves sit the guillemots and auks, arranged as on parade, with their white breasts to the sea, and so close that a hailstone could not pass between them.

The puffins take the highest station, and, though scarcely visible, betray themselves by their flying backwards and forwards.

The noise of such a multitude of birds is confounding, and in vain a person asks a question of his nearest neighbour.

The harsh tones of the kittiwakes are heard above the whole, the intervals being filled with the monotonous note of the auk, and the softer voice of the guillemot.

When Graba, from whose travels this description is principally drawn, visited the Vogel-berg, he was tempted by the sight of a crested cormorant to fire a gun, but what became of it, he remarks, it was impossible to ascertain.

The air was darkened by the birds roused from their repose.

Thousands hastened out of the chasm with a frightful noise, and spread themselves over the ocean.

The puffins came wandering from their holes, and regarded the universal confusion with comic gestures.

The kittiwakes remained composedly in their nests, whilst the cormorants tumbled headlong into the sea.

Similar great congregations of the feathered race appear where the shores are rocky high, and precipitous, but this is strikingly the case, where ----"The northern ocean, in vast whirls, Boils round the naked melancholy isles Of farthest Thule; and the Atlantic surge Pours in among the stormy Hebrides.

Who can recount what transmigrations there Are annual made?

what nations come and go?

And how the living clouds on clouds arise?

Infinite wings!

till all the plume-dark air And rude resounding shore are one wild cry."

[Verse: "He rained flesh upon them as dust, and feathered fowls like as the sand of the sea."

--PSALM LXXVIII.

] 1327. Most terrestrial birds, unacquainted with man, exhibit a remarkable tameness, and are slow in acquiring a dread of him, even after repeated lessons that danger is to be apprehended from his neighbourhood.

Mr. Darwin speaks of a gun as almost superfluous in the unfrequented districts of South America, for with its muzzle he pushed a hawk off the branch of a tree.

Once, while lying down, a mocking thrush alighted on the edge of a pitcher, made of the shell of a tortoise, which he was holding in his hand, and began very leisurely to sip the water, even allowing him to handle it while seated on the vessel.

In Charles Island, which had been colonised about six years, he saw a boy sitting by a well with a switch in his hand, with which he killed the doves and finches as they came to drink; and for some time had been constantly in the habit of waiting by the well for the same purpose, to provide himself with his dinners.

In the Falkland Islands, at Bourbon, and at Tristan d'Acunha, the same tameness was noticed by the early visitors.

On the other hand, the small birds in the arctic regions of America, which have never been persecuted, exhibit the anomalous fact of great wildness.

From a review of various facts, Mr. Darwin concludes, "first, that the wildness of birds with regard to man is a particular instinct directed against him, and not dependent on any general degree of caution arising from other sources of danger;

secondly, that it is not acquired by individual birds in a short time, even when much persecuted; but that in the course of successive generations it becomes hereditary.

Comparatively few young birds in any one year have been injured by man in England, yet almost all, even nestlings, are afraid of him; many individuals, however, both at the Galapagos and at the Falklands, have been pursued and injured by man, but yet have not learned a salutary dread of him."

[Verse: "As a bird that wandereth from her nest; so is a man that wandereth from his place."

--PSALM XXVII.

] 1328. Numerous species of birds may be regarded as the favourites of nature on account of the gracefulness given to their shape, and the richly-coloured plumage with which they are adorned, as evidenced in the gaudy liveries of many of the parrot tribe, and the forms and hues of the birds of paradise.

But they are especially interesting to man for the faculty of song with which they are endowed; in some, "most musical, most melancholy," in others, sprightly and animating, inspiriting the sons of toil under the burdens peculiar to their station.

It deserves to be remarked, as an instance of compensation and adjustment, that whilst the birds of the temperate zone are far inferior to those of tropical climes in point of beauty, they have far more melodious notes in connection with their less attractive appearance.

1329. From the powerful means of locomotion possessed by several of the bird tribe, and their great specific levity, air being admitted to the whole organisation as water to a sponge, it might be inferred, that the entire atmosphere was intended to be their domain, so that no species would be limited to a particular region.

The common crow flies at the rate of twenty-five miles an hour; the rapidity of the eider-duck, _Anas mollissima_, is equal to ninety miles an hour; while the swifts and hawks travel at the astonishing speed of a hundred and fifty miles in the same time.

It is true that some species have a very extensive range, as the nightingale, the common wild goose, and several of the vulture tribe.

The same kind of osprey or fishing-eagle that wanders along the Scottish shores appears upon those of the south of Europe, and of New Holland.

The lammergeyer haunts the heights of the Pyrenees, the mountains of Abyssinia, and the Mongolian steppes; and the penguin falcon occurs in Greenland, Europe, America, and Australia.

In general, however, like plants and terrestrial quadrupeds, the birds are subject to geographical laws, definite limits circumscribing particular groups.

The common grouse of our own country affords a striking exemplification of this arrangement, as it is nowhere met with out of Great Britain;

and other examples occur of a very scanty area containing a species not to be found in any other region.

The celebrated birds of paradise we exclusively confined to a small part of the torrid zone, embracing New Guinea and the contiguous islands; and the beautiful Lories are inhabitants of the same districts, being quite unknown to the New World.

Parroquets are chiefly occupants of a zone extending a few degrees beyond each tropic, but the American group is quite distinct from the African, and neither of these have one in common with the parrots of India.

The great eagle is limited to the highest summits of the Alps; and the condor, which soars above the peak of the loftiest of the Andes, never quits that chain.

Humming-birds are entirely limited to the western hemisphere, where a particular species is sometimes bounded by the range of an island, while others are more extensively spread, the _Trochilus flammifrons_, common to Lima, being observed by Captain King upon the coast of the Straits of Magellan, in the depth of winter, sucking the flowers of a large fuchsia, then in bloom in the midst of a shower of snow.

Among the birds incapable of flight, which rival the quadrupeds in their size, the intertropical countries of the globe have their distinct species, presenting similar general features of organisation, as the ostrich of Africa and Arabia, the cassowary of Java and Australia, and the touyou of Brazil.

In the arctic regions, we meet with species peculiar to them, the _Strix laeponicus_ or Lapland owl, and the eider-duck, an inhabitant of the shores, from whose nests the eider-down is obtained.

Several families of maritime birds are likewise limited to particular oceanic localities.

Approaching the fortieth parallel of latitude, the albatross is seen flitting along the surface of the waves, and soon afterwards the frigate and other tropical birds appear, which never wander far beyond the torrid zone.

It thus appears, that, notwithstanding the great locomotive powers of birds, particular groups have had certain regions assigned to them as their sphere of existence, which they are adapted to occupy, and to which they adhere in the main, though it is easy to conceive of natural causes occasionally constraining to a migration into new and even distant territories.

Captain Smyth informed Mr. Lyell, that when engaged in his survey of the Mediterranean, he encountered a gale in the Gulf of Lyons, at the distance of between twenty and thirty leagues from the coast of France, which bore along many land-birds of various species, some of which alighted on the ship, while others were thrown with violence against the sails.

In this manner, many an islet in the deep, after ages of solitude and silence, uninterrupted except by the wave's wild dash, and the wind's fierce howl, may have received the song of birds, forced by the tempest from their home, and compelled to seek a new one under its direction.

[Verse: "There is a path which no fowl knoweth, and which the vulture's eye hath not seen."

--JOB XVIII.

] 1330. There is no feature more remarkable in the economy of birds than the periodical migrations, so systematically conducted, in which five-sixths of the whole feathered population engage.

In the case of North America, according to an estimate by Dr. Richardson, the passenger-pigeons form themselves into vast flocks for the journey, one of which has been calculated to include 2,230,000,000 individuals.

We are familiar with the cuckoo as our visitor in spring, and with the house-swallow as our guest through the summer, the latter usually departing in October to the warmer regions of the south, wintering in Africa, returning again when a more genial season revives its insect food.

By cutting off two claws from the feet of a certain number of swallows, Dr. Jenner ascertained the fact of the same individuals re-appearing in their old haunts in the following year, and one was met with even after the lapse of seven years.

The arctic birds migrate farther south, when the seas, lakes, and rivers become covered with unbroken sheets of ice; the swans, geese, ducks, divers, and coots flying off in regular phalanxes to regions where a less rigorous winter allows of access to the means of life.

Hence, soon after, we lose the swallows, we gain the snipes and other waders, which have fled from the hard frozen north to our partially frozen morasses, where their ordinary nutriment may still be obtained.

The equinoctial zone, where the seasonal change is that of humidity and drought furnishes an example of the same phenomenon.

As soon as the Orinoco is swollen by the rains, overflows its banks, and inundates the country on either side, an innumerable quantity of aquatics leave its course for the West India islands on the north, and the valley of the Amazon on the south, the increased depth of the river, and the flooded state of the shores, depriving them of the usual supply of fish and insects.

Upon the stream decreasing, and retiring within its bed, the birds return.

[Verse: "The Lord is my light and my salvation; whom shall I fear?

the Lord is the strength of my life; of whom shall I be afraid?"

--PSALM

XXVII.

] 1331. A comparison between the quadrupeds of the Old and New Worlds is in every point strikingly in favour of the former.

Not only has the western continent no animals of such giant bulk as those of the eastern, but no examples of such high organisation, such power and courage, as the African lion and the Asiatic tiger display.

Buffon's remark must indeed be considerably modified, respecting the cowardice of the American feline race; for the jaguar of the woods about the Amazon, when attacked by man, will not hesitate to accept his challenge, will even become the assailant, nor shrink from an encounter against the greatest odds.

The following passages from the writings of Humboldt show that this transatlantic animal is not to be despised:-- "The night was gloomy; the Devil's Wall and its denticulated rocks appeared from time to time at a distance, illuminated by the burning of the savannahs, or wrapped in ruddy smoke.

At the spot where the bushes were the thickest, our horses were frightened by the yell of an animal that seemed to follow us closely.

It was a large jaguar, that had roamed for three years among these mountains.

He had constantly escaped the pursuit of the boldest hunters, and had carried off horses and mules from the midst of enclosures; but, having no want of food, had _not yet_ attacked men.

The negro who conducted us uttered wild cries.

He thought he should frighten the jaguar; but these means were of course without effect.

The jaguar, like the wolf of Europe, follows travellers even when he will not attack them; the wolf in the open fields and in unsheltered places, the jaguar skirting the road, and appearing only at intervals between the bushes."

The same illustrious observer also remarks,-- "Near the Joval, nature assumes an awful and savage aspect.

We there saw the largest jaguar we had ever met with.

The natives themselves were astonished at its prodigious length, which surpassed that of all the tigers of India I had seen in the collections of Europe."

Still these were extraordinary specimens of the race, and leave the fact undoubted, that the most formidable of the western _Feræ_ has no pretensions to an equality with his congener, the tyrant of the jungles of Bengal.

1332. In vain also we look among the tribes of America for a rival in outward appearance to the giraffe, so remarkable for its height, its swan-like neck, gentle habits, and soft expressive eye; while of the animals most serviceable to mankind--the horse, the ox, the ass, the goat, and the hog--not a living example of either was known there before its occupancy by the Europeans.

But, however inferior the animal race of the New may be as compared to those of the Old world, the balance between the two appears to have been pretty equal in remote ages; geological discovery has disproved the assertion of Buffon, that the creative force in America in relation to quadrupeds never possessed great vigour, and has established the fact, that it is only the more recent specimens of its energy that are upon an inferior scale.

The relics of the unwieldly magatherium, of the gigantic sloth, and armadillo-like animals, discovered in great abundance imbedded in its soil, prove that at a former period it swarmed with monsters of equal bulk with those that now roam in the midst of Africa and Asia.

The estuary deposit that forms the plains westward of Buenos Ayres, and covers the gigantic rocks of the Bando Oriental, appears to be the grave of extinct gigantic quadrupeds.

[Verse: "But wild beasts of the desert shall lie there; and their houses shall be full of doleful creatures; and owls shall dwell there, and satyrs shall dance there."

--ISAIAH XIV.

] 1333. There are various animals which are very widely dispersed, enduring the extremes of tropical heat and of polar cold, which are either in a wild condition or in a state of domestication.

Wild races, considered to be varieties of the domestic dog, occur in India, Sumatra, Australia, Beloochistan, Natolia, Nubia, various parts of Africa, and both the Americas; while in subjection to man, the dog is his faithful companion, and has followed his steps into every diversity of climate and of situation to which he has wandered.

The north temperate zone of the Old Continent appears to be the native region of the ox, which passes in Lapland within the arctic circle, and has been spread over South America since its first introduction by the Spaniards.

The horse, originally an inhabitant of the temperate parts of the Old World, has shared in a similar dispersion, and now exists in the high latitude of Iceland, in the desolate regions of Patagonia, and roams wild in immense herds over the Llanos of the Orinoco, leading a painful and restless life in the burning climate of the tropics.

Humboldt draws a striking picture of the sufferings of these gifts of the Old World to the New, returned to a savage state in their western location.

"In the rainy season, the horses that wander in the savannah, and have not time to reach the rising grounds of the Llanos, perish by hundreds amidst the overflowings of the rivers.

The mares are seen, followed by their colts, swimming, during a part of the day, to feed upon grass, the tops of which alone wave above the waters.

In this state they are pursued by the crocodiles; and it is by no means uncommon to find the prints of the teeth of these carnivorous reptiles on their thighs.

Pressed alternately by excess of drought and of humidity, they sometimes seek a pool, in the midst of a bare and dusty soil, to quench their thirst; and at other times flee from water and the overflowing rivers, as menaced by an enemy that encounters them in every direction.

Harassed during the day by gad-flies and mosquitoes, the horses, mules, and cows find themselves attacked at night by enormous bats, that fasten on their backs, and cause wounds which become dangerous, because they are filled with acaridæ and other hurtful insects.

In the time of great drought, the mules gnaw even the thorny melocactus (melon-thistle), in order to drink its cooling juice, and draw it forth as from a vegetable fountain.

During the great inundations, these same animals lead an amphibious life, surrounded by crocodiles water-serpents, and manatees.

Yet, such are the immutable laws of nature, their races are preserved in the struggle with the elements, and amid so many sufferings and dangers.

When the waters retire, and the rivers return into their beds, the Savannah is spread over with a fine odoriferous grass; and the animals of old Europe and Upper Asia seem to enjoy, as in their native climates the renewed vegetation of spring."

1334. The first colonists of La Plata landed with seventy-two horses, in the year 1535, when, owing to a temporary desertion of the colony, the animals ran wild; and in 1580, only forty-five years afterwards, it had reached the Straits of Magellan.

The ass has a more restricted range than the horse, not being capable of enduring so great a degree of cold, though usually far from being considered a delicate animal.

To the warmer parts of the temperate zone, between the 20th and the 40th parallels of latitude, the ass seems best adapted, not propagating much beyond the 60th, and only occurring in a state of degeneration beyond the 52nd.

The sheep and goat tribe are widely spread, equally supporting the extremes of temperature.

According to Zimmerman, the _Argali_ or _Mouflon_, the original race of sheep, still exists on all the great mountains of the two continents; and the _Capricorn_ and _Ibex_, the ancestors of the common goat inhabit the high European elevations.

From the 64th degree of north latitude the hog is met with all over the old continent, and also in the islands of the Indian Ocean, peopled by the Malay race; and since its introduction into the New World, it has diffused itself over it, from the 50th parallel north as far as Patagonia.

Originally the cat was not known in America, nor in any part of Oceanica; but it has now spread into almost every country of the globe.

Among animals entirely wild, the most extensively diffused, are the fox, hare, squirrel, and ermine; but the species are different in every region of the world; nor is there perhaps one example to be found of a species perfectly identical naturally existing in distant localities of the earth.

[Verse: "His going forth is from the end of the heaven, and his circuit unto the ends of it; and there is nothing hid from the heat thereof."

--PSALM XIX.

] Respecting the _internal constitution and heat of the earth_, differences of opinion, and some very wild speculation have existed.

We find in Humboldt's "Cosmos" the following remarks:-- 1335. "It has been computed at what depths liquid and even gaseous substances, from the pressure of their own superimposed strata, would attain a density exceeding that of platinum, or of iridium; and in order to bring the actual degree of ellipticity, which was known within very narrow limits, into harmony with the hypothesis of the infinite compressibility of matter, Leslie conceived the interior of the Earth to be a hollow sphere, filled with "an imponderable fluid of enormous expansive force."

Such rash and arbitrary conjectures have given rise, in wholly unscientific circles, to still more fantastic notions.

The hollow sphere has been peopled with plants and animals, on which two small subterranean revolving planets, Pluto and Proserpine, were supposed to shed a mild light.

A constantly uniform temperature is supposed to prevail in these inner regions, and the air being rendered self-luminous by compression, might well render the planets of this lower world unnecessary.

Near the north pole, in 82 deg.

of latitude, an enormous opening is imagined, from which the polar light visible in Aurora streams forth, and by which a descent into the hollow sphere may be made.

Sir Humphry Davy and myself were repeatedly and publicly invited by Captain Symmes to undertake this subterranean expedition; so powerful is the morbid inclination of men to fill unseen spaces with shapes of wonder, regardless of the counter-evidence of well-established facts, or universally recognised natural laws.

Even the celebrated Halley, at the end of the 17th century, hollowed out the earth in his magnetic speculations; a freely rotating subterranean nucleus was supposed to occasion, by its varying positions, the diurnal and annual changes of the magnetic declination.

It has been attempted in our own day, in tedious earnest, to invest with a scientific garb that which, in the pages of the ingenious Holberg, was an amusing fiction."

The following are among the speculations which Humboldt thus severely but justly condemns:-- "The increase of temperature observed is about 1 deg.

Fahr.

for every fifteen yards of descent.

In all probability, however, the increase will be found to be in a geometrical progression as investigation is extended; in which case the present crust will be found to be much thinner than we have calculated it to be.

And should this be found to be correct, the igneous theory will become a subject of much more importance, in a geological point of view, than we are at present disposed to consider it.

Taking, then, as correct, the present observed rate of increase, the temperature would be as follows: Water will boil at the depth of 2,430 yards.

Lead melts at the depth of 8,400 yards.

There is red heat at the depth of 7 miles.

Gold melts at 21 miles.

Cast iron at 74 miles.

Soft iron at 97 miles.

And at the depth of 100 miles there is a temperature equal to the greatest artificial heat yet observed; a temperature capable of fusing platina, porcelain, and indeed every refractory substance we are acquainted with.

These temperatures are calculated from Guyton Morveau's corrected scale of Wedgwood's pyrometer; and if we adopt them, we find that the earth is fluid at the depth of 100 miles from the surface, and that even in its present state very little more than the soil on which we tread is fit for the habitation of organised beings."

The above is to be found in Mr. Timbs's "Things not Generally Known," a little book which professes to set people right upon points on which they are in error!

[Verse: "He hath filled the hungry with good things; and the rich he hath sent empty away."

--LUKE I.

] Upon this subject Mr. Hunt, in his "Poetry of Science," says:-- 1336. "A question of great interest, in a scientific point of view, is the temperature of the centre of the earth.

We are, of course, without the means of solving this problem; but we advance a little way onwards in the inquiry by a careful examination of subterranean temperature at such depths as the enterprise of man enables us to reach.

These researches show us, that where the mean temperature of the climate is 50 deg.

, the temperature of the rock at 59 fathoms from the surface is 60 deg.

; at 132 fathoms it is 70 deg; at 239 fathoms it is 80 deg.

;

being an increase of 10 deg.

at 59 fathoms deep, or 1 deg.

in 35. 4 feet; of 10 deg.

more at 73 fathoms deeper, or 1 deg.

in 43. 8 feet; and of 10 deg.

more at 114 fathoms still deeper, or 1 deg.

in 64. 2 feet.

Although this would indicate an increase to a certain depth of about one degree in every fifty feet, yet it would appear that the rate of increase diminishes with the depth.

It appears therefore probable, that the heat of the earth, so far as man can examine it, is due to the absorption of the solar rays by the surface.

The evidences of intense igneous action at a great depth cannot be denied, but the doctrine of a cooling mass, and of the existence of an incandescent mass, at the earth's centre, remains but one of those guesses which active minds delight in."

Upon the subject of _hunger_ and _thirst_, by which living creatures are prompted to feast upon the bounties of nature, Sir Charles Bell says, in "Appendix to Paley's Natural Theology:"-- 1337. "Hunger is defined to be a peculiar sensation experienced in the stomach from a deficiency of food.

Such a definition does not greatly differ from the notions of those who referred the sense of hunger to the mechanical action of the surfaces of the stomach upon each other, or to a threatening of chemical action of the gastric juice on the stomach itself.

But an empty stomach does not cause hunger.

On the contrary, the time when the meal has passed the stomach is the best suited for exercise, and when there is the greatest alacrity of spirits.

The beast of prey feeds at long intervals; the snake and other cold-blooded animals take food after intervals of days or weeks.

A horse, on the contrary, is always feeding.

His stomach, at most, contains about four gallons, yet throw before him a truss of tares or lucerne, and he will eat continually.

The emptying of the stomach cannot, therefore, be the cause of hunger.

"The natural appetite is a sensation related to the general condition of the system, and not simply referable to the state of the stomach;

neither to its action, nor its emptiness, nor the acidity of its contents; nor in a starved creature will a full stomach satisfy the desire of food.

Under the same impulse which makes us swallow, the ruminating animal draws the morsel from its own stomach.

1338. "Hunger is well illustrated by thirst.

Suppose we take the definition of thirst--that it is a sense of dryness and constriction in the back part of the mouth and fauces; the moistening of these parts will not allay thirst after much fatigue or during fever.

In making a long speech, if a man's mouth is parched, and the dryness is merely from speaking, it will be relieved by moistening, but if it comes from the feverish anxiety and excitement attending a public exhibition, his thirst will not be so removed.

The question, as it regards thirst, was brought to a demonstration by the following circumstance.

A man having a wound low down in his throat, was tortured with thirst; but no quantity of fluid passing through his mouth and gullet, and escaping by the wound, was found in any degree to quench his thirst.

"Thirst, then, like hunger, has relation to the general condition of the animal system--to the necessity for fluid in the circulation.

For this reason, a man dying from loss of blood suffers under intolerable thirst.

In both thirst and hunger, the supply is obtained through the gratification of an appetite; and as to these appetites, it will be acknowledged that the pleasures resulting from them far exceed the pains.

They gently solicit for the wants of the body; they are the perpetual motive and spring to action."

[Verse: "Let us hear the conclusion of the whole matter; Fear God, and keep his commandments: for this is the whole duty of man."

--ECCLESIASTES XII.

]