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estat trea CORIANDER.-Coriandrum Sativum. Staigos This is one of the favourite spices which will be
found in most of our gardens. The following is the UT botanical description :
“Coriander is an umbelliferous plant akin to the parsley in family characteristicks. The flowers
grow in an umbel, and are individually small and CENA 933 ? Jwhite. The leaves are much divided, and smooth. op 29 The seeds are employed, from their aromatick na.
ture, in culinary purposes, and hence their round C
and finished shape is well known. In the umbellifArcherous plants the fruit uniformly separates into two
similar halves, which are the seeds; but in the coriander they continue united after they are ripe. If
we examine the seed we shall perceive very readily BALM OF GILEAD.
that it is compounded of two, while a reference to « • Balm,' is the famous resin obtained from the the parsley, or any other example of the umbellifBaisamodendron Gileadense, or balm of Gilead tree, erous family, will illustrate the peculiarity of the which was a native of, and almost peculiar to, the coriandrum in this respect." 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 "I resolve,” says Bishop Beveridge, "never to said by Theophrastus to be so odoriferous, that it speak of a man's virtues before his face, nor of his filled a large space with its perfume. The author | faults behind his back." / 12412
Toks VOL. 5.--37
نق، و و و
'This is called the law of inertia, and expresses
the entire indifference of matter to motion or rest. Ai the request of many of our subscribers, we The proposition that a body will never begin to move shall give a course of articles on Natural Philoso- of itself needs no proof: it is the conclusion of phy, for the use of schools and families. The arti- tion we conclude that there is a power in action to
universal observation. Wherever we observe mocles will be compiled from the best authorities, and produce it. The other part of the law, that motion include the usual number of branches taught under is
, in its nature, as permanent as rest, and that it is in that head in our schools, commencing with
a right line, is far from being a self-evident, or even
an obvious truth, Limited observation would lead MECHANICKS.
to the conclusion that all matter has a tendency to * The science which treats of forces and of mo- resi, and such has long been, and still is, à common tion is called Mechanicks. It had, probably, its errour. The same limited observation led some of origin in the construction of machines, and an im- the ancient astronomers to imagine ihaf all bodies portant branch of it, practical mechanieks, investi. when forced into a state of motion naturally moved gates their construction and effects. Forces acting in curved lines. There is, however, abundant proof upon
bodies may either produce rest or motion. In of the permanence of motion; and if friction and the former case they are treated of under staticks, the resistance of the air, the two most universal in the latter under dynamicks.
obstacles to the motion of bodies near the surface of Hydrostaticks and hydraulicks respectively treat the earth, could be entirely removed, instances of of fluids, at rest or in motion. When a body is permanent motion would be still more numerous. In acted on by two or more forces which counteract proportion as they are -removed, or as bodies are
. each other, so that no motion is produced, the body beyond their influence, we observe a tendency in the and the forces are said to be in a state of equi- motions of those bodies to become more and more librium. 'The conditions of equilibrium form the permanent. A marble, rolled on the grass, subject of staticks.
stops ; on a carpet, it moves longer; on a floor, still 1. A body acted upon by two equal and opposite longer; and on smooth level ice, where the wind is forces will remain at rest. In this case either of the not unfavourable, it continues very long in motion. two opposite forces may be made up of several In a vacuum, where the resistance of air is not felt, parallel forces. It is then said to be the resultant two windmills, whose pivots have equal friction, and of those forces.
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 spin3. 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, of the motion is proportioned to the diminution of acting in a direction and with an intensity repre- friction and resistance. We can hardly avoid the sented by the side which would be necessary to conclusion that a body once put in motion, would, if complete the polygon.
left to itself, continue to move with undiminished All the changes which come under our observa- velocity, tion 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 me- towards a centre by the universal force of gravity. chanicks.
This force does not diminish their velocity, but deAll motions are found to take place in conformity flects them continually from the right line in which to a few universal principles deduced from observa- they tend to move. If this central force were sustion and confirmed by experiment. These princi- pended, they would all shoot forward into space, ples have often been placed at the beginning of trea and the harmony of their motions would cease. tises on mechanicks, under the name of the laws of Some force similar to this central tendency is motion. If not expressed in this manner, the truths always in action whenever we see bodies move they declare, making an essential part of the princi- in curve lines. ples of the science, are necessarily introduced under The stone, to which a boy gives accumulated force some other form. Their comprehensiveness adapts by whirling it round in a sling, is, for a time, kept in them to our purpose, and they are here quoted in the its circle by the central force represented by the language of Newton :
string ; when let loose it darts forward in the air, 1. “Every body perseveres in its state of rest, or turning not to the right or left, until the atmosphere of uniform motion in a right line, unless it is com- ical resistance destroys its motion, or the force of pelled to change that state by forces impressed gravity bends it to the ground. A full tumbler of thereon.”
water placed in a sling, and made to vibrate with
gradually increasing oscillations, may at last be made spent in giving motion to the inert mass. After. to revolve in a circle about the hand, each drop ward, with far less exertion, he keeps up the motion, tending to move out in a straight line from the centre, being required to supply that portion only which is and therefore remaining safe in the tumbler, whose destroyed by the obstacles of the road. The motion bottom is always farthest from the centre. In a communicated to a body, if not destroyed by some corn-mill the grain is poured gradually into a hole in force, is accumulated. Thus a nail is driven in by the centre of the upper mill-stone. The weight of all the force of the hand, accumulated through the the stone pulverizes the corn, while its circular mo- whole time of the descent of the hammer. The tion throws it out as fast as it is ground into a cavity knowledge of this fact gives the means of increasaround the stone. When a vessel, partly full of ing the effective force of a moving power in a very water, is suspended by a cord, and made to turn great degree. A force of fifty pounds communicated rapidly round, the water, in its tendency to move every second to a loaded wheel will, if not diminished out in a straight line, recedes from the centre, and is by friction or other cause of waste, enable it to overgradually heaped up against the sides of the vessel, come a resistance of five hundred pounds once in sometimes even leaving a portion of the bottom dry. every ten seconds. Such a wheel is called a fly. Water moving rapidly in the stream of a river, or wheel. the tide of the sea forced violently through a narrow
II. “ The alteration of motion is ever proportioned passage between opposite rocks, not unfrequently to the motive force impressed, and is made in the forms a whirlpool on the same principle. Bent out direction of the right line in which that force is imof its course by a projecting ledge, it departs, as if pressed." This is only a statement that a double. reluctantly, from a straight line, and heaps itself up force generates a double motion; that motion cantowards the circumference of the circle in which it not increase or diminish itself, nor turn to the right is compelled to move. To this cause, too, it is or left without cause. In consequence of this, two owing, however little we might expect such a conse- or more forces acting at once on a body in different quence,
that a river, passing through an alluvial soil, directions cause it to take a direction different from and once turned from its onward channel, continues that of either force, and, if one of them is a variable to pursue a meandering course to the sea. Driven, or constantly acting force, to move in a curve line. by any cause, to one side, it strikes the bank with This is called the composition of forces, the single all its violence, is repelled, and rebounds with the motion impressed upon the body being considered as same force to the opposite side, continually wearing composed of the several motions which the forces the two banks, and leaving a larger space on the acting separately would have produced. A boat, , inner side of the bends.
rowed at the rate of three miles an hour directly The force with which a body constrained to move from the bank of a river which runs at the rate of in a circle tends to go off in a straight line is called two miles an hour, is acted on at once by the force the centrifugal force. Advantage is taken of it in of the rowers and that of the current, and will be many processes of the arts, and in all circular mo- found, at the end of an hour, three miles from the tions of machinery. The clay of the potter is bank, and two miles below the point from which it : placed on the centre of a swiftly revolving table, and started, having moved in a diagonal line between the while his hand shapes it the centrifugal force causes directions of the two forces. it to assume the desired dimensions. A globe, or The resolution of forces is the reverse of this. A sheet of molten glass, is in a similar manner made single force is considered as resolved into two or to expand itself. The legs of a pair of tongs, sus- more others. A ship, sailing on a side wind, is sent pended by a cord, and made to revolve by its twisting forward by a part only of its force. The other part or untwisting, will diverge in proportion to the velo- has no effect, or that only of driving her out of her city of the revolution.
The steam-governer of Watt is constructed and III.“ To every action there is always opposed an acts on this principle. Weights are attached to two equal reaction; or the mutual actions of two bodies rods, to which a circular motion is communicated by on each other are equal and in opposite directions." the machinery which is to be governed. If the If you press a stone with your finger, the finger is motion be so rapid as to cause these rods to diverge equally pressed by the stone. A horse drawing from each other beyond a certain angle, they act upon a load is drawn backward by its whole weighi, upon a valve which partly closes and diminishes the and, if he succeed in moving it, it can only be with supply of steam. With a slower motion the rods a velocity proportioned to the excess of his strength collapse, and the valve is opened.
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 ball is propelled, but with a velocity as much less as quantity of motion in one second will impart double its weight is greater. If, in the side of a vessel of the quantity in two seconds. A ship does not yield water, hanging perpendicularly by a cord, a hole be at once to the impulse of the wind when the sails are opened, the vessel will be pushed back from the set ; its motion increases as new portions are succes- perpendicular by the reaction of the jet of water, and sively imparted. A horse does not start at once with will remain so while it flows. A consequence of a carriage into his utmost speed ; his force is at first this law is, that the earth is attracted by each body
on its surface as much as it attracts, and that when the plain or torrent below, with considerable accu
10 a stone falls toward the earth the earth rises to racy, by letting fall a stone and observing the time meet it. The force with which a body acts is esti- of its fall. It would only be necessary to make mated by its velocity and mass conjointly, and is allowance for the resistance of the air, which, for called its momentum. Thus, if two balls of one and small velocities, is not very great. two pounds weight respectively be moving with the The same cause which communicates motion to a same velocity, the larger has wice 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 bounded by straight or curve lines, the centre of this accumulated motion would alone carry it through gravity coincides with the centre of magnitude. four times sixteen or sixty-four feet in the third If a body of any shape be suspended freely from second, and the continued action of gravitation car- any one point of its surface, the straight line exter:dries it once sixteen; so that it actually descends five ing from that point to the centre of the earth will times sixteen or eighty feet during the third second. pass through the centre of gravity. This line is In the fourth second it would, in the same manner, called the line of direction. The centre of gravity descend seven times sixteen feet; in the fifth, nine may, therefore, sometimes be found, practically, by times sixteen, &c., the series of odd numbers ex- suspending a body successively from two of its pressing the distances passed through in the suc- points, and observing the point where the lines of cessive seconds. By adding these numbers we find direction cross each other. The centre of gravity that at the end of two seconds the body will have of a triangle is at one third the distance from the descended four times sixteen feet; at the end of the middle of the base to the vertex; that of a cone third, nine times sixteen; at the end of the fourth, and of a pyramid at one fourth the same distance. 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 gravity must rise almost perpendicularly, and move feet. The following table exhibits, 1, the space for a great distance before it ceases to tend to fall fallen through in the successive seconds ; 2, the back to its place. Hence their stability, and hence whole space fallen through at the end of a number the propriety of giving to steeples, monuments, and of seconds; and, 3, the final velocity: ;
other buildings of great height, a pyramidical or Time,
conical figure. Those carriages are most secure 1. Successive spaces, 1 3
which are hung low, and have the wheels far apart. 3. Final velocity,
Whatever raises the centre of gravity or narrows By means of this table, a traveller standing on the the base allows the line of direction more easily to summit of a cliff might ascertain its height above pass without it, and consequently diminishes stability.
2. Total spaces,
1 2 3 4 5 6 7 8 9 10 seconds.
5 7 9 11 13 15 17 19 times 16 ft.