must have eaten the reptiles from liking them, and just quoted, informs us it was reported in his time, not from antipathy to them. Besides, there are not that only two enclosures of small extent were known in those places of the country to which chiefly the to produce this tree, which were in some part of ibis resorts, very many serpents for the birds to eat, Syria. Bruce describes it, however, as growing in either from liking or disliking. Water-serpents are Azab, and all along the coast of Babelmandel. The not, we believe, very numerous in the Nile; and the balsam of Gilead is about fourteen feet high, with land-serpents of Egypt are chiefly, if not exclusive- diverging branches that bear leaves at their extremly, found in the dry and sandy places in which the ities. These leaves are pennate or winged, like ibis seldom if ever seeks its food; besides, the bill those of the terebinth, and evergreen in their duof the ibis is not of a very serpent-killing character; ration. The fruit is a berry, or rather a drupe, of an for though it is stouter and harder than the bills of egg shape, marked with four seams, and with two the true snipes, and even than that of the curlews, cells. The kataf of the Arabians is afforded by a it is still a bill of the same class. Birds with the species of this genus, as is also the kafal. They more characteristick bill of this form feed chiefly are both of them odoriferous resins, very famous in upon small mollusca, and other little animals which the East." find inny sound any they find on the moist surface of the ground, or in #44 olivendo tirult coleg the sludge; and so far as has been observed in mod-out to tear outing todas ma coiled anqu ern times, the ibis seeks its food in similar places, sate toliau te ho and hence we may conclude, that it feeds on substances of a similar kind. Birds which do feed on serpents are always very long in the tarsi, which is not the case with the ibis, and they also have pow erful bills. Cultrirostral birds, such as cranes and storks, and the other birds of that family, are more likely to perform this office than such a bird as the ibis. It may be true, however, that the American species of Tantalus, which is a hard-billed bird, and jed does eat reptiles, may have been confounded with the ibis in ancient times, as it has sometimes been by modern naturalists."

"BALM,' is the famous resin obtained from the Baisamodendron Gileadense, or balm of Gilead tree, which was a native of, and almost peculiar to, the land of Judea. It is related to the terebinth and other trees, which are noted for the fragrant gums' which they yield. A small piece of this resin is said by Theophrastus to be so odoriferous, that it filled a large space with its perfume. The author VOL. 5.--37

"I resolve," says Bishop Beveridge, "never to speak of a man's virtues before his face, nor of his faults behind his back."

NATURAL PHILOSOPHY.

At the request of many of our subscribers, we shall give a course of articles on Natural Philosophy, for the use of schools and families. The articles will be compiled from the best authorities, and include the usual number of branches taught under that head in our schools, commencing with

MECHANICKS.

THE science which treats of forces and of motion is called Mechanicks. It had, probably, its origin in the construction of machines, and an important branch of it, practical mechanicks, investigates their construction and effects. Forces acting upon bodies may either produce rest or motion. In the former case they are treated of under staticks, in the latter under dynamicks.

Hydrostaticks and hydraulicks respectively treat of fluids, at rest or in motion. When a body is acted on by two or more forces which counteract each other, so that no motion is produced, the body and the forces are said to be in a state of equilibrium. The conditions of equilibrium form the subject of staticks.

1. A body acted upon by two equal and opposite forces will remain at rest. In this case either of the two opposite forces may be made up of several parallel forces. It is then said to be the resultant of those forces.

This is called the law of inertia, and cxpresses the entire indifference of matter to motion or rest. The proposition that a body will never begin to move of itself needs no proof: it is the conclusion of universal observation. Wherever we observe motion we conclude that there is a power in action to produce it. The other part of the law, that motion is, in its nature, as permanent as rest, and that it is in a right line, is far from being a self-evident, or even an obvious truth. Limited observation would lead to the conclusion that all matter has a tendency to rest, and such has long been, and still ís, a common errour.. The same limited observation led some of the ancient astronomers to imagine that all bodies when forced into a state of motion naturally moved in curved lines. There is, however, abundant proof of the permanence of motion; and if friction and the resistance of the air, the two most universal obstacles to the motion of bodies near the surface of

the earth, could be entirely removed, instances of permanent motion would be still more numerous. In proportion as they are removed, or as bodies are beyond their influence, we observe a tendency in the motions of those bodies to become more and more permanent. A marble, rolled on the grass, soon stops; on a carpet, it moves longer; on a floor, still longer; and on smooth level ice, where the wind is not unfavourable, it continues very long in motion. In a vacuum, where the resistance of air is not felt, two windmills, whose pivots have equal friction, and which are set in motion by equal forces, continue to 2. If two forces act with reference to each other move equally long whatever be the position of their obliquely upon a body, they may be counteracted by vanes. In the air, the one whose vanes cut the air, a third (called also their resultant). If the two will move much longer than the one whose vanes forces be represented in direction and intensity by are opposed to it. A pendulum in a vacuum, having two contiguous sides of a parallelogram, their result only the stiffness of the riband by which it is suswill be represented in direction and intensity by pended to overcome, will vibrate for a whole day. its diagonal. This is called the parallelogram of A spinning-top in the same situation, retarded only forces. by the friction of its point, is said to continue spin

3. If several forces, acting at once upon a poly-ning for hours. In all these cases the continuance gon, they may be counteracted by a single force, acting in a direction and with an intensity represented by the side which would be necessary to complete the polygon.

of the motion is proportioned to the diminution of friction and resistance. We can hardly avoid the conclusion that a body once put in motion, would, if left to itself, continue to move with undiminished velocity.

All the changes which come under our observation in this science are the consequence of motions The heavenly bodies, moving in free space, subproduced by the action of a few great elementary ject to no opposing influence, keep on in their path forces. The consideration of the motions which with a velocity which has remained unabated since take place among the particles only of one or of first they were launched from the hand of the Crea several bodies comes within the department of tor. They move not, indeed, in straight lines, but chymistry. Those motions which affect masses are in curves, as they are drawn towards each other and the appropriate subject of the second part of mechanicks.

All motions are found to take place in conformity to a few universal principles deduced from observation and confirmed by experiment. These principles have often been placed at the beginning of treatises on mechanicks, under the name of the laws of motion. If not expressed in this manner, the truths they declare, making an essential part of the principles of the science, are necessarily introduced under some other form. Their comprehensiveness adapts them to our purpose, and they are here quoted in the language of Newton:

I. "Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon."

towards a centre by the universal force of gravity. This force does not diminish their velocity, but deflects them continually from the right line in which they tend to move. If this central force were suspended, they would all shoot forward into space, and the harmony of their motions would cease. Some force similar to this central tendency is always in action whenever we see bodies move in curve lines.

The stone, to which a boy gives accumulated force by whirling it round in a sling, is, for a time, kept in its circle by the central force represented by the string; when let loose it darts forward in the air, turning not to the right or left, until the atmospherical resistance destroys its motion, or the force of gravity bends it to the ground. A full tumbler of water placed in a sling, and made to vibrate with

gradually increasing oscillations, may at last be made to revolve in a circle about the hand, each drop tending to move out in a straight line from the centre, and therefore remaining safe in the tumbler, whose bottom is always farthest from the centre. In a corn-mill the grain is poured gradually into a hole in the centre of the upper mill-stone. The weight of the stone pulverizes the corn, while its circular motion throws it out as fast as it is ground into a cavity around the stone. When a vessel, partly full of water, is suspended by a cord, and made to turn rapidly round, the water, in its tendency to move out in a straight line, recedes from the centre, and is gradually heaped up against the sides of the vessel, sometimes even leaving a portion of the bottom dry. Water moving rapidly in the stream of a river, or the tide of the sea forced violently through a narrow passage between opposite rocks, not unfrequently forms a whirlpool on the same principle. Bent out of its course by a projecting ledge, it departs, as if reluctantly, from a straight line, and heaps itself up towards the circumference of the circle in which it is compelled to move. To this cause, too, it is owing, however little we might expect such a consequence, that a river, passing through an alluvial soil, and once turned from its onward channel, continues to pursue a meandering course to the sea. Driven, by any cause, to one side, it strikes the bank with all its violence, is repelled, and rebounds with the same force to the opposite side, continually wearing the two banks, and leaving a larger space on the inner side of the bends.

The force with which a body constrained to move in a circle tends to go off in a straight line is called the centrifugal force. Advantage is taken of it in many processes of the arts, and in all circular motions of machinery. The clay of the potter is placed on the centre of a swiftly revolving table, and while his hand shapes it the centrifugal force causes it to assume the desired dimensions. A globe, or sheet of molten glass, is in a similar manner made to expand itself. The legs of a pair of tongs, suspended by a cord, and made to revolve by its twisting or untwisting, will diverge in proportion to the velocity of the revolution.

The steam-governer of Watt is constructed and acts on this principle. Weights are attached to two rods, to which a circular motion is communicated by the machinery which is to be governed. If the motion be so rapid as to cause these rods to diverge from each other beyond a certain angle, they act upon a valve which partly closes and diminishes the supply of steam. With a slower motion the rods collapse, and the valve is opened.

spent in giving motion to the inert mass. Afterward, with far less exertion, he keeps up the motion, being required to supply that portion only which is destroyed by the obstacles of the road. The motion communicated to a body, if not destroyed by some force, is accumulated. Thus a nail is driven in by all the force of the hand, accumulated through the whole time of the descent of the hammer. The knowledge of this fact gives the means of increasing the effective force of a moving power in a very great degree. A force of fifty pounds communicated every second to a loaded wheel will, if not diminished by friction or other cause of waste, enable it to overcome a resistance of five hundred pounds once in every ten seconds. Such a wheel is called a flywheel.

II. "The alteration of motion is ever proportioned to the motive force impressed, and is made in the direction of the right line in which that force is impressed." This is only a statement that a double. force generates a double motion; that motion cannot increase or diminish itself, nor turn to the right or left without cause. In consequence of this, two or more forces acting at once on a body in different directions cause it to take a direction different from that of either force, and, if one of them is a variable · or constantly acting force, to move in a curve line. This is called the composition of forces, the single motion impressed upon the body being considered as composed of the several motions which the forces acting separately would have produced. A boat, rowed at the rate of three miles an hour directly from the bank of a river which runs at the rate of two miles an hour, is acted on at once by the force of the rowers and that of the current, and will be found, at the end of an hour, three miles from the bank, and two miles below the point from which it started, having moved in a diagonal line between the directions of the two forces.

The resolution of forces is the reverse of this. A single force is considered as resolved into two or more others. A ship, sailing on a side wind, is sent forward by a part only of its force. The other part has no effect, or that only of driving her out of her

course.

III. "To every action there is always opposed an equal reaction; or the mutual actions of two bodies on each other are equal and in opposite directions." If you press a stone with your finger, the finger is equally pressed by the stone. A horse drawing upon a load is drawn backward by its whole weight, and, if he succeed in moving it, it can only be with a velocity proportioned to the excess of his strength over the reaction of the load. A magnet and piece In consequence of the centrifugal force occasioned of iron attract each other equally; and if, when in by the rotation of the earth, the weight of bodies at the sphere of mutual attraction, one is fixed and the the equator is diminished the 289th part. If the other free, whichever is free will be drawn to the earth revolved on its axis in eighty-four minutes, the other. Two equal boats, drawn towards each other loose parts near the equator would be projected from by a rope, act in the same manner; if both are free, the surface. Another consequence or particular of they meet in the middle. When a gun is discharged, the law of inertia is, that motion is communicated it recoils with a force equal to that with which the gradually. A force which communicates a certain quantity of motion in one second will impart double the quantity in two seconds. A ship does not yield at once to the impulse of the wind when the sails are set; its motion increases as new portions are successively imparted. A horse does not start at once with a carriage into his utmost speed; his force is at first

ball is propelled, but with a velocity as much less as its weight is greater. If, in the side of a vessel of water, hanging perpendicularly by a cord, a hole be opened, the vessel will be pushed back from the perpendicular by the reaction of the jet of water, and will remain so while it flows. A consequence of this law is, that the earth is attracted by each body

the plain or torrent below, with considerable accuracy, by letting fall a stone and observing the time of its fall. It would only be necessary to make allowance for the resistance of the air, which, for small velocities, is not very great.

on its surface as much as it attracts, and that when a stone falls toward the earth the earth rises to meet it. The force with which a body acts is estimated by its velocity and mass conjointly, and is called its momentum. Thus, if two balls of one and two pounds weight respectively be moving with the The same cause which communicates motion to a same velocity, the larger has twice the momentum falling body would gradually destroy that of a body of the smaller, since each pound of the larger has ascending. A ball projected upward with the velothe same velocity as the ball of a single pound. A city of 1000 feet per second would, therefore, rise body of small weight may therefore be made to pro- with a uniformly retarded motion to the height from duce the same mechanical effect as a large one, by which a body must fall to acquire that velocity. The sufficiently increasing its velocity. The cannon-ball phenomena of accelerated and retarded motion are of modern times is not less effectual in battering beautifully exhibited by Atwood's machine for that down walls than the massy battering-ram of the an- purpose. In moving down an inclined plane, a solid cients. The forces which may be employed to give body is urged by a portion of the force of gravitation, motion to machines are called mechanical agents or which is continually smaller as the plane is nearer first movers. They are water, wind, steam, gun- to a horizontal position. When it is horizontal, the powder, and the strength of man and other animals. whole weight of the body is sustained by the plane. They may be indirectly referred to three independent The velocity acquired by bodies moving down planes sources-gravity, heat, and animal strength. of different inclinations, is the same as they would Gravity. A body falling from a state of rest, de- have acquired by falling freely through a distance scends 16 feet, nearly (16.095), in one second; but, equal to the perpendicular height of the plane. It as all the motion which is communicated by gravita- is necessary, in the construction of machines, cartion remains in it, and it receives an accession of riages, buildings, bridges, and ships, and in many motion every indefinitely small portion of the first other cases, to ascertain exactly the centre of gravity second, it is moving more rapidly at the end of the of the whole and of each part; since, if the centre second than at any previous time, and with that of gravity, in any body or system of bodies, be supmotion alone, if it continued uniform, would descend ported, the whole must remain firm, and in a state through twice sixteen or thirty-two feet in the next of rest, in every possible position. The various second; but during this next second as much motion problems arising from this necessity, have been is communicated as during the first, and consequently solved with great accuracy, and on fixed principles. the body descends through three times sixteen or In all regular solids of uniform density, whether forty-eight feet in this next second. The whole of this accumulated motion would alone carry it through four times sixteen or sixty-four feet in the third second, and the continued action of gravitation carries it once sixteen; so that it actually descends five times sixteen or eighty feet during the third second. In the fourth second it would, in the same manner, descend seven times sixteen feet; in the fifth, nine times sixteen, &c., the series of odd numbers expressing the distances passed through in the successive seconds. By adding these numbers we find that at the end of two seconds the body will have descended four times sixteen feet; at the end of the third, nine times sixteen; at the end of the fourth, sixteen times sixteen, &c.; the whole distance Stability, in every case, depends upon the position fallen through at the end of any number of seconds of the centre of gravity in reference to the base. being found by multiplying the square of that number The nearer it is to the base, and the further the line by sixteen feet. Such is the simple and remarkable of direction falls from each part of the perimeter of law of the descent of bodies by the uniformly ac- the base, the greater is the stability. The sphere 'celerated velocity produced by gravitation. The rests equally in every position, because the centre velocity acquired in one second is sufficient of itself of gravity is at the same distance from every part to carry a body through twice sixteen feet; that of the surface; it is unstable in every position, as it acquired in two seconds would carry it four times rests on a single point of the plane; and it yields to sixteen feet; that acquired in three seconds, through the smallest force, as the centre of gravity does not six times sixteen feet, &c., the velocities possessed rise when the sphere revolves. In order that the at the end of any number of seconds being repre- pyramid or cone may be overturned, the centre of sented by twice that number multiplied by sixteen feet. The following table exhibits, 1, the space fallen through in the successive seconds; 2, the whole space fallen through at the end of a number of seconds ; and, 3, the final velocity:

bounded by straight or curve lines, the centre of gravity coincides with the centre of magnitude.

If a body of any shape be suspended freely from any one point of its surface, the straight line extending from that point to the centre of the earth will pass through the centre of gravity. This line is called the line of direction. The centre of gravity may, therefore, sometimes be found, practically, by suspending a body successively from two of its points, and observing the point where the lines of direction cross each other. The centre of gravity of a triangle is at one third the distance from the middle of the base to the vertex; that of a cone and of a pyramid at one fourth the same distance.

and

gravity must rise almost perpendicularly, and move for a great distance before it ceases to tend to fall back to its place. Hence their stability, and hence the propriety of giving to steeples, monuments, other buildings of great height, a pyramidical or conical figure. Those carriages are most secure which are hung low, and have the wheels far apart. Whatever raises the centre of gravity or narrows the base allows the line of direction more easily to pass without it, and consequently diminishes stability.

Hence we see the imprudence of rising in carriages, or boats which are in danger of being overset, and hence the danger of high loads on wagons, where the roads are not perfectly level. The force of gravity is not often employed directly as a mechanical agent, or prime mover. Those most frequently employed to give motion to machinery are water, wind, heat, and the strength of animals.

Water acts by its weight and by the velocity which it acquires from falling, in consequence of its weight. Wind acts by its volume or mass and its velocity. Both these agents are variable, and both act in a straight line. Heat, as given out by combustible materials, produces steam or gas, or gives motion to air by making it lighter, and thus causing it to rise. The steam or gas, when formed, has a tendency to expand itself, presses against the sides of the vessel which contains it, and endeavours to escape with a force proportioned to the heat and pressure to which it is exposed. When allowed to escape in only one direction, it necessarily generates motion in a straight line. Steam, as usually employed, generates motion, which is alternately in one direction and the opposite. The strength of animals is commonly made to act upon some centre of resistance, by drawing, pushing, or pressing, and produces variable motions, naturally in a straight line but often in a curve. The motions or pressures produced by all these agents are capable of being compared with those produced by weights. They might all be referred to a common standard, the unit of which should be the force required to raise a given weight a certain number of feet in a given time.

The mechanical agents are employed to measure time, to move ships and carriages, to raise weights, to shape wood and work metals, to overcome the resistance of air, of water, and of cohesion, to draw out and form materials, and to combine them into new fabricks. To apply them to accomplish any one of these effects, requires the intervention of some mechanical contrivance. Such a mechanical contrivance, whether consisting of a few or of many parts, is called a machine. A machine has been defined, "a system of bodies, fixed or moveable, so connected together that a movement impressed on one of them shall be transmitted to the others."

THE above engraving represents one of the curiosities of the far-famed Hoboken, opposite the city of New York, denominated the " Sybil's Cave."

It is an excavation into the solid rock of about thirty feet. The front is fashioned in the Gothick style, as will be seen by reference to the engraving A short distance inside the cave, is a spring of water slightly impregnated with magnesia.

The object of a machine is often vaguely supposed romantick places in the country. Situated on the Two years ago, Hoboken was one of the most to be to produce or augment power. It can never have this effect. The resistance of the fixed and banks, and overlooking the mighty Hudson, the bay the friction of the moveable parts will always con- and harbour, and city of New York, and laid out in sume a part of the power of the prime mover. The beautiful and shaded walks, varied by nature and by real object of every machine is to increase or dimin-art-it had become the favourite resort both of the ish the velocity of the moving force, to change its citizens and visiters to the "commercial emporium.” direction, to accumulate its action and expend it at a single effort, to distribute the force among a great number of small resistances, or to divide the force of a resistance so that it may be overcome by a series of actions, or by the continued action of the moving power. A machine may combine the action of several movers, and employ one to regulate the others, so that the final effect shall be perfectly uniform. The pendulum, the governer, and the flywheel are employed for this purpose.

[The mechanical powers in our next.]

"Disappointments sink the heart of man, but the renewal of hope gives consolation."

"Self-preservation is the first law of nature."

One

It still retains some of its beauties and ornaments, but the land of the spoiler has been there. thousand dirt-carts are employed, in destroying its verdant lawns-turning them into "city lots." And its quiet and romantick retreats are soon to give way to the sound of the hammer and the axe.

It may be that these improvements are much need ed, and that the island of Manhattan, is not larg enough for all the stores that may be wanted, bu we could have wished the speculators had chosen some other place than Hoboken, for these improve

ments.