THE VISCACHA, OR PRAIRIE-DOG, OF THE PAMPAS.

(Lagostomus trichodactylus. Brookes. Callomys viscaccia. Isid. Geoff. Marmot Diana. Griff. Trans. Cuvier.)

devour both European wheat and Indian | corn, with great avidity, despising grass when either can be obtained. Hence the biscacha stations are seldom to be met with in the desert plains, but with certainty indicate the proximity of Spanish settlements; and it is a matter of surprise, that I have never seen the biscacha in the territories, (although well supplied with crops of all kinds,) either of the Abipones, or of Guaranis. They daily heap up, at the entrances of their burrow, dry bones, chips of wood, and whatever odds and ends they may meet with; but for what purpose they collect such things, it is impossible to conjecture.

"The Spanish settlers occasionally spend an idle hour in hunting them; pouring buckets of water into their subterranean retreats, when the creatures, to avoid drowning, issue out into the plain, and no refuge presenting, are killed with sticks. Unless very old, their flesh is not considered despicable even by the Spaniards."

holes of these animals are also inhabited by vast numbers of small owls, which sit during the day, gazing on the passing travellers, and making a very ludicrous appearance. The parts of the road most frequented by the biscacha, are generally overrun by a species of wild melon, bitter to the taste. Whether it thrives particularly in the manure of this animal, or whether the biscacha chooses his hole near this running plant, does not seem to have been ascertained."

The viscacha is an animal of the rodent order, (rodentia,) which comprises also the rabbit, marmot, porcupine, and all animals distinguished by two large incisores, or cutting teeth, in each jaw, separated, by a space void of teeth, from the grinders, which have a perpendicularly laminated structure.

In size, this animal, when fully grown, is nearly as large as our common badger. Above, it is of a blackish grey; beneath, white. The head is large and obtuse, and The abbe Jolis, a Spaniard, who dwelt a whitish band, beginning on the nose, for many years in South America, also de- passes across the face, beneath each eye, scribed the visacha, or biscacha, (for the to the root of the ear, producing a sort of word is differently spelled,) in a work pub-crescent-shaped mask, when the face is lished in 1789, and afterwards in 1801. D'Azzora gave, in his work on the Quadrupeds of Paraguay, a more detailed sketch, from which succeeding naturalists have generally taken their accounts, and which rendered it evident that the animal could no longer be retained among the hares, (lepus,) where it had been placed.

Among recent travellers who have noticed the viscacha, we may mention Proctor, who, in his narrative of a journey across the Cordillera of the Andes, ob

serves:

"The whole country, from Buenos Ayres to San Luis de la Panta, is more or less burrowed by an animal between a rabbit and a badger, called the biscacha, which renders travelling dangerous, particularly by night, their holes being so large and deep, that a horse is almost sure to fall if he steps into one of them. The biscacha never ventures far from its retreat, and is seldom seen till the evening, when it comes out to feed; and hundreds may be observed sporting around their holes, and making a noise very similar to the grunting of pigs. Their flesh is much liked by the people, and they are remarkably fat, and on that account, when caught at any distance from their holes, are easily run down; they will, however, defend themselves from a dog for a considerable time. The

seen in front. The sides of the lips are furnished with a tuft of thickly-set whiskers, composed of long black bristles; and from the angles of the mouth, across the cheeks, below the band, extends a brush of black bristles, stouter than the whiskers, but shorter, the lowermost being sharply pointed. This brush reaches the angle of the jaw, and forms a true beard; it does not, however, end quite abruptly, but may be traced by bristly hairs intermingled with the fur, across the shoulder, as far as the middle of the back. The ears are moderate, the fore-legs are rather slender and short, the toes are four, and the whole of the palm is bare, the hind legs long, and something resembling those of a kangaroo, though not so disproportionately large. They are, however, formed so as to enable the animal to sit up; the metatarsal bones being long, and the heel furnished with a naked callous sole, before which is a part covered with hair. The toes are three, of which, as in the kangaroo, the middle one is much elongated; all are furnished with strong nails and naked pads. At the end is a sketch, which shows the resemblance to the same part of the kangaroo. The tail is of moderate length, covered with greyish brown hairs, of which the longest form a fringe on the upper surface; it is generally kept like squirrel's,

M.

retroverted on the back. The incisor teeth | several beautiful specimens in the Musee are remarkably large and strong. Our drawing was taken from one of the

du roi, at Paris.

(Sketch of Under-surface of Hind Foot.)

ATMOSPHERIC PRESSURE.

mass of air to the surface, and an oppressive density would be produced; if the latter was the only force, the atmosphere would be so rarified, that neither animal nor vegetable substances could exist. But the Creator has so arranged and balanced these two opposing forces, that the atmosphere around the earth is in the best possible state to sustain the creatures with whom he has peopled the world.

SOLAR light, when uninfluenced by an interfering body, moves in right lines, but in passing through a fluid, a vapour, or a gas, it is bent or refracted from its direction. An upright stick, plunged to some depth in water, appears broken, and the eye does not give us an accurate idea of its real situation and position, nor do we see any of the celestial bodies in their real places, because their light is bent out of its But as we ascend from the surface of straight course, in passing through our at- the earth, the attraction of gravitation demosphere. A knowledge of this fact ena- creases, and the expansive power being less bles us to approximate to a determination and less under control, the atmosphere is of the extent of our atmosphere; for, it in a greater state of rarification. It would has been discovered that, at a height of be possible to ascend so high above the forty-five miles, it has the power of refract-level of the sea, that the air would be in too ing or bending the solar rays. How far it extends beyond this, we cannot very readily determine, but from the production of sound at much greater heights, we may at least deduce that this is not its limit.

It will readily be perceived that the density of the atmosphere must become less and less as we ascend from the surface of the earth, for all gases and vapours are not only elastic, but are capable of compression into a smaller bulk than they would occupy if uninfluenced. So great is the expansibility of atmospheric air, that if it were perfectly free from the control of all attractive forces, it would expand itself indefinitely. But the force of gravity, or, in other words, the attraction of gravitation, which causes bodies to fall to the earth, has a power over the atmosphere, and keeps it around the world in which we live. There are, therefore, two forces acting in different directions, and both are necessary to keep the atmosphere in its present state; there is the attraction of the earth, which draws it to the surface, and the expansibility of the air, which gives it a tendency to throw itself off. If the former acted alone, it would bring the whole

attenuated a state to support animal life. The atmosphere may, therefore, be considered as composed of layers, or strata, the lowest being the most dense.

As the air is material, it must have weight, and consequently exert a pressure upon all the bodies which it surrounds. The pressure exerted upon bodies at the surface of the earth is equal to about 15lbs. on every square inch. The body of an average-size man presents a surface of about 2000 square inches, and consequently such a man must sustain a pressure equal to 30,000 pounds. This statement, however, is often misunderstood, and it is imagined that this weight is pressing down the human body, or that a man has to carry it upon his shoulders; but this is an erroneous conception of the manner in which the atmospheric pressure is exerted. The body is surrounded by air, and the pressure is equal in every direction, so that the exterior force upon the body supports rather than oppresses, while the air which is contained within, prevents the external force from producing any injurious effect.

It will require no arguiment to prove

that the air exerts a downward pressure, | and the reader may soon convince himself that it also has an upward pressure. If we take a tumbler, and, filling it with water, place a piece of pasteboard or card at the top, the glass may be inverted without spilling the water, for the card is kept firmly in its place by the upward pressure of the atmosphere, although it has to support the weight of the water.

The Magdenburgh hemispheres are generally employed to prove that the atmosphere exerts a pressure in every direction. Two hollow brass hemispheres are so formed that their lips may fit closely together, and be air-tight. Into one of these hemispherical cups an open tube is fitted, which is furnished with a stop-cock, and a handle that may be unscrewed at pleasure. When the instrument is to be used, remove the handle, and screw the hemisphere to the plate of an air-pump, and placing the other hemisphere upon it, exhaust the air they contain; turn the stop-cock, and remove them from the pump. The handle may now be replaced, and two strong persons will be unable to separate the cups, for the interior air being removed, there is no force to counteract the pressure upon the exterior surface. This experiment admirably illustrates the principle, that the pressure is the same in every di

rection.

In the study of this remarkable property of the atmosphere we are led to admire its exceedingly beautiful adaptation to the constitution of animal and vegetable bodies. When God placed man upon the earth to pass his state of probation, he had prepared a world for his residence, that was exactly adapted to sustain his life, and to increase all his rational pleasures. And even after his fall, when he was put under a new state of probation, by the mercy of God, these adaptations were not withdrawn, but all the sources of enjoyment that were before derived from the material creation, were still oper to him.

The atmosphere by which the earth is surrounded is necessary for the support of animal and vegetable life in its application to the respiratory structure. But this is not its only use, for if it exerted no pressure upon bodies, the vessels of the animal and vegetable systems would be unable to sustain the expansion of the fluids they contain. Now, if it had pleased God to place man in a state of misery, the removal of a part of the pressure which rests upon his animal frame would have

accomplished the purpose. A sufficient power might have been left to prevent the destruction of life, and yet so much migh have been taken away, as to render that life miserable. We may therefore, even in the study of the material creation, gather from the mercies of God, incitements to love him, when the heart has been once reconciled by a confiding trust in the greater work of redemption through Christ. (To be continued.)

UTILITY OF WATER.

If we would have a familiar illustration of the importance of the use of water, in the daily and hourly occurrences of life, let us in imagination accompany an individual of moderate rank and condition in society, from the time of his rising in the morning till the hour of sleep at night, in order to observe the utility of water in administering either directly or indirectly to his various wants and habits. How great is the comfort, to say nothing of the salubrity of the practice, which results to him from the application of water to the surface of the body, by means either of the bath or any simpler process! and, again, the change of the linen, in which he is partially clothed, is rendered equally comfortable and salutary, in consequence of its having been previously submitted to the process of washing. The infusion of coffee, or of tea, which is probably an essential part of his earliest meal, could not have been prepared without water; neither could the flour, of which his bread consists, have been kneaded; nor the food of his subsequent meal, the broths and most of the vegetables at least, have been rendered digestible; and, with respect to his common beverage, whether milk, or any form of fermented liquor, water still constitutes the main bulk of that beverage.

So far the use of water is directly and immediately necessary to his comfort and subsistence; but its indirect and remote necessity is equally observable in all that surrounds him. There is scarcely an article of his apparel, in some part of the preparation of which water has not been necessarily employed; in the tanning of the leather of his shoes; in the dressing of the flax of which his linen is made; in the dyeing of the wool of his coat, or of the materials of his hat. Without water the china or earthen cups, out of which he drinks, could not have been turned on the lathe; nor the bricks, of which his house is constructed, nor the mortar by which