Gambar halaman
PDF
ePub

Account of the Great Speckled Diver or Loon. From White's Natural ist's Calendar.

AS one of my neighbours was traversing Wolmer forest from Bramshot across the moors, he found

and the heat communicated is in every case proportional to the quantity of absorption. It appears, from some ingenious experiments of Mr. Bouguer, that we receive only four-fifths of the rays of a vertical sun; and when that luminary ap proaches the horizon, the portion of this light, which reaches the surface of the earth, is much smaller. Thus, at an elevation of 20 degrees, it is one-half; at that of 10 degrees, one-third; and at that of five degrees, one-eighth. Hence, the sun-beams are most powerful on the summits of lofty mountains, for they suf、 fer the greatest diminution in passing through the dense air of the lower regions. If the air derived its heat from the surface of the earth, those countries would be warmest which enjoyed the greatest quantity of sun-shine. The Eritish islands are shrouded in clouds nine months of the year; yet our climate is milder than that of the same parallel on the continent, where the sky is generally serene. The elevated town of Quito, exposed to a brilliant sun, enjoys a temperate air; while the Peruvian plains, shaded with fleecy clouds, are parched with heat. Were the reasoning in the text to be admitted, we would conclude, that the tops of mountains are warmer than their basis. To say that air, much rarified, is not suscep-. tible of heat, is a very extraordinary assertion, since we are acquainted with no substance whatever that may not be heated. Besides, a more intense cold may be artificially produced than what prevails in the lofty regions of the atmosphere. We must recur to other principles for the true solution of the fact. It is indifferent what portion of the air first receives the heat; the effect depends entirely on the nature of its distribution. If the atmosphere were of an uniform density throughout, the heat would, at all heights, be likewise the same. But as the den sity varies according to the altitude, the distribution of heat is affected by that circumstance, and follows a certain corresponding law. I would gladly develope the principles from which this theory is deduced, but the popular nature of the present treat se forbids all abstract discussion. I shall, therefore, content myself with giving a table of the diminution of heat at different altitudes.

[subsumed][subsumed][merged small][subsumed][ocr errors][subsumed][subsumed]

The diminution of heat, on the ascent, is not quite so great in extensive continents: for the intercourse between the rare and the dense portions of the atmosphere is, ia this case, necessarily slow, and the heat, which is principally formed at the surface, will only be partially dispersed.

It is a common mistake to suppose, that the same heat obtains, at a certain depth, in every part of the globe. The fact is, that heat, originally derived from the sun, is communicated very slowly to the matter below the surface, which, therefore, does not feel the vicissitude of seasons, but retains the average tempera ture of the climate for many ages. Hence the utility of examining the heat of springs which is the same with that of the substances through which they flow.

The

und a large uncommon bird flut ering in the heath, but not woundd, which he brought home alive. On examination it proved to be Colymbus glacialis, Linn.: the great speckled diver or loon, which S most excellently described in Willoughby's ornithology.

Every part and proportion of this bird is so incomparably adapted to its mode of life, that in no instance do we see the wisdom of God in the creation to more advantage. The head is sharp, and smaller than the part of the neck adjoining, in order that it may pierce the water; the wings are placed forward, and out of the centre of gravity, for a purpose which shall be noticed hereafter; the thighs quite at the podex, in order to facilitate diving; and the legs are fat, and as sharp backwards al. most as the edge of a knife, that in striking they may easily cut the water; while the feet are palmat. ed, and broad for swimming, yet so folded up when advanced for. ward to take a fresh stroke, as to be full as narrow as the shank. The two exterior toes of the feet are longest; the nails flat and broad resembling the human, which

give strength and increase the power of swimming. The foot, when expanded, is not at right angles to the leg or body of the bird: but the exterior part inclining towards the head forms an a cute angle with the body; the in tention being not to give motion in the line of the legs themselves, but by the combined impulse of both in an intermediate line, the line of the body.

Most people know, that have observed at all, that the swimming of birds is nothing more than a walking in the water, where one foot succeeds the other as on the land; yet no one, as far as I am aware, has remarked that diving fowls, while under water, impel and row themselves forward by a motion of their wings, as well as by the impulse of their feet: but such is really the case, as any person may easily be convinced, who will observe ducks when hunted by dogs in a clar pond. Nor do I know that any one has given á reason why the wings of diving fowls are placed so forward: doubt. less, not for the purpose of promoting their speed in flying, since that position certainly impedes it;

The following table exhibits the average heat of places on the level of the sea, computed by the celebrated astronomer, professor Meyer, for every five degrees of Jatitude.

[merged small][merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

Average Temperature. ༡༣-༠

49

45

414

36

35

334

324

32

By comparing this table with the preceding, it is easy to discover, for any ∙12titude, the altitude of the curve of congelation, or where the average tempetature is 32°.-E. E.

but

[ocr errors][ocr errors]

but probably for the increase of their motion under water, by the use of four oars, instead of two ; yet were the wings and feet nearer together, as in land birds, they would, when in action, rather hinder than assist one another.

This Coly mbus was of conside. rable bulk, weighing only three drachms short of three rounds a. voirdupoise. It measured in length from the bill to the tail which was very short), two feet; and to the extremities of the toes fout inches more; and the breadth of the wings expanded was 42 inches. A person attempted to eat the body, but found it very strong and rancid, as is the flesh of all birds living or fish. Divers or loons, though bred in the most rortherly parts of Europe, yet are seen with us in very severe winters; and on the Thames are called sprat loons, because they prey much on that sort of fish.

The legs of the Colymbi and Mergi are placed so very backward, and so our of all centre of gravity, that these birds cannot walk at all. They are called by Lin. næus compedes, because they move on the ground as if shackled, or fettered.

word flambant (flaming), because it appears, at a distance, like a flame of fire. He generally inha. bits in swampy grounds, and salt marshes, in the waters of which he constructs his hest, by raising out of the moisture, of a foot deep, a little hillock of mud, a foot and a half high. He makes a hole in the summit of this litle hillock; in this the hen deposits two eggs and hatches them, with her feet sunk in the water, by means of the extreme length of her legs. When several of these birds are sitting at the same time on their eggs, in the midst of a swamp, you would take them, at a distance, for the flames of a configration, bursting from the bosom of the waters.

Other fowls present contrasts of a different kind on the same shores. The pelican, or wide throst, is a bird white and brown, provided with a large bag under its beak, which is of exce sive length. Out he gres every morning to store his bag with fish: a d. the supply of the dy having been accomplished, he perches on some pointed rocks on a level with the water, where he stands immoveable till the evening, says father Du Tertre*, "as in a state of profound sorrow, with -the head drooping, from the weight of his long bill, and eyes fixed on the agitated ocean, as motionless as a statue, of marble.". On the dusky strand of those seas may fre. quently be distinguished herons THERE is seen, on the shores white as snow, and in the azure of India, a large and beautiful plains of the sky, the paillencu of a bird, white, and fire-coloured, call very white, skimming through it ed the flaminge, not that it is of almost out of sight: he is someFlemish extraction, but the mamet times glazed over with a bright is derived from the old French red, having likewise the two long

Contr sts and Conor ties between
Animals and the Earth. From Dr.
Hunter's Translation of St. Pierre's
Studits of Nature.

[ocr errors]
[blocks in formation]

feathers of his tail the colour of fire, as that of the South.seas.

In many cases, the deeper that the ground is, the more brilliant are the colours in which the, ani mal, destined to live upon it, is arrayed. We have not, perhaps, in Europe, any insect with richer and gayer clothing than the ster coraceous scarab, and the fly, which bears the same epithet. This last is brighter than burnished gold and steel; the other, of a hearispherical form, is of a fine blue, incin. ing to purple; and in order to render the contrast complete, he exhales a strong and agreeable odour of musk.

Nature has bestowed at once, in the colours of ionoxious animals, contrasts with the ground on which they live, and consonances with that which is adjacent, and has su peradded the instinct of employing these alternately, according as good or bad fortune prompts. These wonderful accommodations may be remarked in most of our small birds, whose flight is feeble, and of short duration. The grey lark finds her subsistence among the grass of the plains? Does any thing terrify her, she glides away, and takes her station between two little clods of earth, where she becomes invisible. On this post she remains in such perfect tranquillity, as hardly to quit it, when the foot, of the fowler is ready to crush her.

The same thing is true of the par. tridge. I have no doubt that these defenceless birds have a sense of those contrasts and corresponden. cies of colour; for I have remark. ed it even in insects. In the month

of March last, I observed, by the :
brink of the rivulet which washes
the Gobelins *, a butterfly of the
colour of brick, reposing with ex
panded wings on a tuft of grass.
On my approaching him, he flew
off. He alighted, at some paces dis
tance, on the ground, which, at
that place, was of the same colour
with himself. I approached him
a second time; he took a second
fight, and perched again on a
similar stripe of earth. in a word,
I found it was not in my power
to oblige him to alight on the
grass, though I made frequent at.
tempts to that affect, and though
the spaces of earth which separated
the turfy soil were narrow, and few
in number.

This wonderful instinct is like-
wise conspicuously evident in the
cameleon. This species of lizard,
whose motion is extremely slow,
is indemnified for this, by the in
comprehensible faculty of assum-
ing, at pleasure, the colour of the
ground over which he moves.
With this advantage, he is ena-
bled to elude the eye of his pur
suer, whose speed would soon have
overtaken him. This faculty is in
bis will, for his skin is by no means
a mirror. It reflects only the
colour of objects, and not their
form. What is farther singularly
remarkable in this, and perfectly
ascertained by naturalists, though
they assign no reason for it, he can
assume all colours, as brown, grey,
yellow, and especially green, which
is his favourite colour, but never ·
red. The cameleon has been plac-
ed, for weeks together, amidst
scarlet stuffs; without acquiring the .

[ocr errors]

A small village in the suburbs of Paris, noted for ion, pestry and superb mirrors.

res in fine ta

slightest

slightest shade of that colour. Na. ture seems to have withheld from the creature this shining hue; be cause it could serve only to render him perceptible as a greater distance; and farther, because this colour is that of the ground of no species of earth, or of vegetable, on which he is designed to pass his life.

But, in the age of weakness and inexperience, nature confounds the colour of the harmless animals, with that of the ground on which they inhabit, without committing to them the power of choice. The young of pigeons, and of most granivorous fowls, are clothed with a greenish shaggy coat, resembling the mosses of the nests. Cater. pillars are blind, and have the complexion of the foliage, and of the barks, which they devour. Nay, the young fruits, before they come to be armed with prickles, or inclosed in cases, in bitter pulps, in hard shells, to protect their seeds are, during the season of their expansion, green as the leaves which surround them. Some embryons, it is true, such as those of certain pears, are ruddy or brown; but they are then of the colour of the bark of the tree to which they belong. When those fruits have inclosed their seeds in kernels, or nuts, so as to be in no farther danger, they then change colour. They become yellow, blue, gold-coloured, red, black, and give to their respective ices their natural contrasts. It is strikingly remarkable, that every fruit which has changed colour has seed in a state of maturity.

It is in the countries of the North, and on the summit of cold mountains, that the pine grows, and the fir, and the cedar, and most

part of resinous trees, which shelter man from the snows by the closeness of their foliage, and which furnish him, during the winter season, with torches, and fuel for his fire-side. It is very remark. able, that the leaves of those evergreen trees are filiform, and are extremely adapted, by this confi. guration, which possesses the farther advantage of reverberating the heat, like the hair of animals, for resistance to the impetuosity of the winds, that beat with peculiar vio lence on elevated situations. The Swedish naturalists have observed, that the fattest pines are to be found on the dryest and most sanly regions of Norway. The larch, which takes equal pleasure in the cold mountains, has a very resi. nous trunk.

Mathiola, in his useful commentary on Dioscorides, informs us, that there is no substance more proper than the charcoal of these trees, for promptly melting the iron mi. nerals, in the vicinity of which they peculiarly thrive. They are, besides, loaded with mosses, some species of which catch fire from the slightest spark. He relates, that being obliged, on a certain occasion, to pass the night in the lofty mountains of the strait of Trento, where he was botanizing, he found there a great quantity of larches (larix) bearded all over, to use his own expression, and com, pletely whitened with moss. The shepherds of the place, willing to amuse him, set fire to the mosses of some of these trees, which was immediately communicated with the rapidity of gunpowder touched with a match. Amidst the ob. scurity of the night, the flame and the sparks seem to ascend up to

the

« SebelumnyaLanjutkan »