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variableness of its direction, appear to be rest on the middle of the horizontal bar, the almost inscrutable..
end of each being elevated so as to form an The magnet has no particular form, or dis- acute angle with it. The two oblique bars tinguished external marks, but appears like a should be separated, by drawing them constone. Meteorologists have extracted iron trary ways along the cross bar, towards the from it, but in such scanty proportion, as not natural magnets, keeping thein at the same to pay the expence of fusion. Modero che- | elevation all the way; when removing them mistry has discovered that iron, in its oxyde from the cross-bar, and bringing their north state, pervades all nature: but the maguet | and south ends in contact, then applying attracts it only in its metallic form. . them again to it as before, and repeating this
We will now proceed to examine the known four or five times; after which, performing properties and laws of magnetism; in which the same operation with the other surface of useful science we shall find much in the ex- | the cross-bar, it will have acquired a permatreme subtilty of its nature to admire, much nent magnetism and polarity. Small needles in its elaborate affections to amuse, and in its for compass boxes do not require this proresults every thing to excite our admiration, i cess, but may be rendered magnetic by friction, astonishment and gratitude.
merely passing them three or four times over We are already acquainted, by our former a magnet in one direction. investigations, with five kinds of attraction: A compass needle while receiving the mag. First, gravitation, which enables all bodies on netic virtue is violently agitated; but when it the surface of the earth to retain their situ- has fully acquired the property, the agitation ations; and, combined with the centrifugal ceases. A magnet loses nothing of its own force, causes all the planetary bodies of our strength by a communication of its property system to revolve round the sun at certain to other bodies, but gains some addition to its distances from that luminary and from each | power by the performance. A north or south, other : secondly, cohesive attraction, which | pole of a magnet, when applied to a bar or keeps the parts of bodies together, and unites needle, produces the contrary polarity; therethem in close compact: tbirdly, chemical fore two magnetic bars should not have the attraction, called affinity, which causes certain 1 poles of the same description placed together, bodies to distinguish each other in preference for that position will diminish their indivito other substances introduced into a com- | dual power. poanded mass, and to unite together : fourthly, Each point of a magnet may be considered capillary attraction, which causes fluids to as the pole of a smaller one, tending to prorise in very small tubes (this may be con- duce on the points of the magnet a force connected with cohesive attraction, being only a trary to its own. The degree of this effort different effect perceived of the same cause): will be greater in proportion to the force of fifthly, we have magnetical attraction; the the point, and its nearness to the poles on affections of which the experiments we shall which it acts; hence, a narrow and long bar bave the pleasure of exhibiting will explain. of steel is more powerful than a short and
The tendency of the needle to the north broad one. and south, is called its direction. Its variation li Whatever may be in reality the cause which from due north and south, is called its decli- produces magnetism, we see tbat its nature nation; and its dip below the horizon, its is very subtile and active; hy its passing inclination.
througb substances of the most compact na
ture, and by its virtue remaining unaltered. EXPERIMENT OF COMMUNICATING THE MAGNETIC VIRTUE.
EXPERIMENT ON MAGNETIC ATTRACTION. The magnetic virtue may be communicated This fact may be proved by placing a magto a bar of ir un or steel, by placing two na- | net on one piece of cork, and a piece of steel tural magnets, in a straight line, the north on another, and floating them on water; when, end of the one opposite to the south end of Il both being unconfined, they will approach the other; and at such a distance, that the | each other: and on holding the picce of steel two ends of the bar to be touched may rest || in the hand, the magnet will approach to it separately upon them: the end designed to || with the same velocity as they approached to point north resting on the south pole of the each other when both were at liberty. bar, and rice rersa. Two other steel bars inust | It appears from the foregoing experiment, be placed in such a manner, that the north that the iron being placed near the pole of a end of one and the south end of the other may magnet becomes possessed of a contrary
power. Their inutual attraction may also be the same degree, and thus it is that the magexplained by the laws of action and re-action, vet supports a greater weight by the commuwhich are always equal and opposite to each nication. That this is the true cause of its other.
increased power of attraction is evident by Neither magnetic attraction nor repulsion placing the south pole of another piagnet is affected by an intervening body; but heat below the piece of iron; when the same effect weakens the power of magnetism, and some takes place. Presenting the north pole of a times destroys it: yet its property may be magnet to the first piece of irou produces á restored, though not its power in the same contrary effect; for it diminishes the power degree as before. May not this circumstance of the first mágnet. arise from some of the effluvia having gone!
EXPERIMENT ON THE INCREASING POWER off in consequence of heat? Iron when red hot
OF A MAGNET. is not attracted by the maguet; perhaps its whole affinity with that power has evaporated. Suspend a magnet by a hook from some
Philosophers have in vain endeavoured to fixed point, and attach as much iron to it as it estimate the force with which the magnetic will support together, with a scale, which attraction acts at different distances; but as must also be affixed : and you will find that that law has not yet been fully ascertained, all every day you may put additional weight in that we can infer from their observations and the scale, and the magnet will support it; experiments is that the magnetic power ex-' which shews that its power is constantly in. tends further at one time than at another, and creasing therefore its sphere of action is variable.
It is supposed that the iron, becoming magA magnet cannot support even its own | netic, iucreases the power of the magnet in weight of metal, but its power may be much the manner before described. When the iron increased by means of arming, which is thus' is removed from the magnet, the power of the performed:
latter is rendered weaker than it was before
the experiment was made. This illustrates TO ARM A MAGNET.
the theory of Æpinus, that the magnetic fluid Cut the magnet into a parallelopipedon, and is unequally distributed in a magnet which has let its two poles be parallel planes: place this a fixed polarity, one pole being overcharged, magnet in an armour of soft iron, which, while the other is undercharged with it: and having a cross piece, with a hook attached, that there is always a strong attraction bewill support great weights suspended from it. | tween these contrary poles, in consequence of The advantage gained by arming is very con this unequal distribution of power; but whin siderable, a magnet that will of itself support a piece of iron is presented to either, that, by four or five ounces, will when armed sustain its becoming possessed of a contrary polarity twenty times that weight. A magnet and its to that of the magnet, the power of each end armour may be enclosed in any material ex- || on the other is weakened by the communicacepting iron.
tion, and thereby its individual power inThe power of a magnet may also be aug- creased; for there is in every magnet a strong mented without arming, by simply intro attraction between its poles; but when ducing another piece of iron below that it at another substance, or a magnet, is presented first supports; as is evident on presenting to to either, the effect is stronger by being drawn it a pitce of iron heavier than it can sustain, from the contrary pole. Hence we may sup. and afterwards holding under it another piece pose that a nagnet becomes continually at a snall distance from the former, when the weaker when left alone, so that it is necessary magnet will support what before it could not either to place it in armour, or leave a piece of lift. The cause of this is assigned by Cavallo steel or iron on its poles ; because at these to the last piece becoming magnetic, and so points the powers are at the greatest distance increasing the attraction of the first piece, and from each other's effects. in the following manner. The end of a piece It is not more extraordinary than true, that of iron which is presented wear the north pole the magnetic power may be acquired without of a magnet becomes possessed of the south, the application of a magnet, and by friction while the other extremity possesses the north be made to communicate that power to iroa polarity. Again, the second piece being beld or steel. Rubbing one piece of iron on near to the north pole of the first piece of iron, ll another will produce evidences of the mag. acquires a south polarity. This must in netic virtue; a .d even a certain position of crease the vorth power of the first piece, when either, long continued, will render that effect its south power must also be augmented in Il permanent. The famous philosopher of our
country, Dr. Gilbert, in the sixteenth century," OF THE DECLINATION OF THE NEEDLE. observed that the small bars of a window which The north pole of the magnet, in every part were placed obliquely to the horizon, and of the world, points nearly north; yet it very nearly north and south, by remaining in that seldom she's that direction exactly. Hence situation for many years became magnetic. the magnetic meridian seldom coincides with
The polarity thus communicated may be from the observed meridian of any place on our the carth and its atnosphere ; for all the ef- globe, but generally varies either to the east or fects of magnetism evince that the power is west. This variation is not uniform at difCerived from those sources, though the pecu ferent places, nor does it always agree even in liar directive power cannot be traced to its | the same place; at London, for instance, in primary natural cause. The particles of iron the year 1640 it was 11° east, but now it is 232 being universally diffused through all auinated west. This variation is always reckoned frord rature, as well as in all substances in the earth, | the north, either east or west. The directive may not a magnet have some effect on the power of magnetism, though generally exhianimal economy? As this universal diffu biied by a touched needle, is also evident in sion of irou fully justifies the idea that the small bars of steel or iron freely suspended; niagnetic fluid is one of the elements of the as may be seen by fine pieces of either floating earth and its atmosphere, may we not also on the surface of water ; but to exhibit this conceive the magnetic efHuvia to be equally property, they must remain some hours, when disseminated through the globe, in such bodies they will point nearly, if not exactly, north as do uot exhibit any evidences of its existence : and south. and that its visible effects result from that 1. The directive property of the magnet, acequilibrium being destroyed ?
cording to Dr. Halley's hypothesis, is sup
posed to arise from the current of the magEXPERIENT ON THE ACTION OF THE POLES netic fluid issuing from a central magnetic ON EACH OTHER.
globe, which passing through the earth and The dipping-needle serves to shew the action its atmosphere, causes light bodies to move of the two different poles on each other; for with it. on presenting the north pole of a maguet to To account for the direction of the magnet the south pule of the peedle, it is attracted ; being variable, and this variation not regular but if we present the same pole of the magnet
at the same place, nor in an uniform degree at to the north pole of the needle, it is then re the same time at different places, various pelled and files from the magnet. Strew steel
| hypothesis have been formed, and some truly filings on a pane of glass, and put the north curious and interesting experiments have been pole of a magnet under it, they will then rise made to illustrate them, of which number the on the paper; but on holding the north pole following appears the inost ingenious and of another magnet directly over these filings, satisfactory. they will immediately fall. Dip the north Messrs. de la Hire, senior and junior, formpole of one magnet and the south pole of an
ed a globe out of a very large magnet, and by other in stecl filings, and bring the ends of suspending it, found its poles; they next the bars toward each other; then the filings traced out its equatorial and meridional circles. will unite. But dip the two north poles and The globe was about a foot in diameter, and bring them in contact, and the filings will weighed one hundred pounds. Placing it due recede from each other.
north and south, and in a position that anTwo magnets placed in a straight line at a | swered for the latitude of the place of observasmall distance from each other, the south poletion, they perceived its declension east and of oue opposed to the north pole of the other, west, in regard to situations of places on it. with a pane of glass over them; on sprinkling From these remarks they inferred that the steel filings, and tapping the glass to produce magnetic fluid is diffused through the whole a little motion in the blings, they will arrange earth, and obeys the universal laws of magthemselves in the direction of the magnetic netism; yet they do not explain the causes fluid; those lying between the two poles, and of the different variations of it at the same near the axis, being disposed in straight lines, | place. The regular declination observed on going from the north pole of one magnet to the magnetic globe was owing to the equality the south pole of the other. Reverse the order ef contexture in its parts, and the varying magof the magnets, by placing the two poles of the netic force at different places on its surface same name opposite, and the filings will But as the contexture of the earth is very irrebe arranged in curves receding from each / gular, perhaps that circumstance, unite with other.
|| the numerous processes carrying ou within it,
is the cause of the variation. Perceiving that racteristic of this curious phenomenon, is unthe regular variation on the magnetic globe known. It may be seen, by placing an unarose from its uniform contexture, we may in touched needle on a pivot, and presenting a fer that the inconstancy of the variation of the magaet to it, when it will incline towards needle on the globe of our earth arises from point below our borizon. To counteract this the inequality of its parts. No perfectly sa effect, the mechanist wbo constructs compases, tisfactory hypothesis having yet been formed | files off part of the inclining end, and by that respecting the variation of the needle that can means balances the needle on the pivot. The be authenticated by facts, it is impossible inclination of the needle is as variable as its to foretel what this irregularity will be at a declination. It also varies at different parts future time at any particular place, or other of the earth at the same time. The idea of circumstances depending on that knowledge, the inclination having reference to latitude though derived from the experience of a long I only is a mistake, it being as irregular in that continued series of observations.
respect as the declination; for at Paris in 1900 The ingenious Mr. Canton discovered a new it was 72° 25' north, and at Siena 13° south. variation of the magnetic needle, which he No doubt these variations depend on the same communicated to the Royal Society. Observ- | causes as those of the direction of the needle. ing the direction of a touched needle for a
THEORY OF MAGNETISM. whole day, he perceived that it was never perfectly at rest; that its westeru declination
The whole that can be inferred of the nature from the pole was greatest in the morning, and of the phenomena of the magaet, is briefly least at night ; about noon in a medium of its is this:-hat it attracts bodies in the earth; and diurnal variation. He offers the following that it has a directive power which is variable, rational solution of these phenomena, founded
arising perhaps from the unequal diffusion of on the known fact, that a maguet when heated
the magnetic power in the earth and atmos. loses something of its natural force. He sup
phere, depending on the different constituposes the direction of the needle to be occa tional circumstances of each of them, togetber sioned by the attraction of the magnetic fluid, with the effects of heat and cold on that power. and that the attraction is strongest where the Its attraction is evident on bodies on the earth; heat is weakest; therefore that the needle at and we know that the earth contains bodies sun-rise with us is not so forcibly impelled l of this attractive nature, for from the earth towards the east, because the magnetic force they are procured; and we must suppose its is lessened by the sun's influence; conse || direction depends on the inequality of attracquently the needle points rather more westerly tion in the earth. The variation in that diat that time. When the sun is on our meri irection may also depend on the parts which dian, the variation is not changed, the action contain the attractive power being more or less of the sun on cach side of us being then equal; lieated. These natural and hidden causes being towards evening the needle points more east- || incalculable by us, we never must expect to erly, because it naturally points to the part arrive at a perfect knowledge or estimation of within its range the least heated by the sun. i them.
The magnetic fluid may be either formed EXPERIMENT.
ll of two kinds of elements united by affinity; This effect may be understood by heating a || these elements having a greater tendency to magnet, and placing it on one side of a needle,
each other than to themselves: or the phenoand another magnet in its natural state on mena perceived of attraction and repulsion, in the other side, when the needle will decline
the former case, may be produced by the endeafrom the heated one. Me. Canton perceived, vour of the disturbed effluvium to place itself in from repeated experiments, that the diurnal
equilibrium, and in the latter form its natural variation of the weedle was about 20 minutes
repulsion to itself. The directive power of of a degree, from sun-rise to sun-set. .
the needle, and the mode of constructing comOF THE DIP OF THE MAGNETIC NEEDLE.
passes, are so well known, that it would be
superfluous to introduce them liere The needle bas a dip, or inclination; the eause of which, like every other peculiar cha- il
(Continued from Page 207.)
THE USELESS TOAST.
li which this occurrence plunged Mr. RMR.R- , was one of the most celebrated || very nearly made him have a relapse, and he epicures of his time. Being very rich he only recovered his good humour at the next needed uothing but a good appetite to satisfy llindigestion. it to the fullest extent; and his house was always well stored with every delicacy which
A PLAN FOR THE IMPROVEMENT OF THE money could procure. He would devour a
CULINARY ART. pigeon-pye with the same ease as if it were a || It would be highly beneticial to the culinary twopenoy cheese-cake, swallow truffles likes || art, that all the new discoveries and inventions many cherries, and eat a fricasseed chicken for || which take place during the period of each his luncheon. But his wife, who doubtless year, should be carefully recorded for the feared widowhood, incessantly contradicted Il increase of our present enjoyment, and for the him, and thwarted him in all his tastes, so | advantage of future generations. A periodimuch so, that in order to enjoy himself at his cal work of this nature, which, to avoid the ease he was obliged to shut himself up, and not | frequent expence of stamp duties (which often allow her admittance, in order that he might, || paralizes thought even in its birth) need only without any ohstacle, yield himself up to the appear once a month, would be of infinite delights of epicurism. At length, however, utility. All that the geuius of good living he fell ill; and the remedy prescribed by the || each day delights to invent, would be faithfully faculty was a strong dose of medicine, and a Il recorded; the progress of each ingenious artist strict regimen. This was for our epicure the would be made known, and their constant efmost unwelcome order in the world, and he forts to deserve public approbation ; added to would certainly have very ill complied with it, which a long list of all kind of provisions had it not been for the vigilance of Mrs. R-, would be given, and the whole to conclude who took possession of all his keys, and as with an account of all the celebrated indigessuming the station of his nurse, made him act tions that have taken place, with their causes completely according to her wishes, as is and effects. This work might also become a always the case with those who are confined channel of correspondence between the epito their beds. The medicines were of service; ] Il cures of every country. It would establish a Mr.
R was much relieved, and judged to medium of communication between all large be in a state of convalescence. At length be cities for every thing relating to cookery; each was permitted to eat; and the physician, well || town already celebrated by its alimentary proaware of his weak side, scrupulously ordered || ductions, or that wished to acquire a name, the exact quantity of food he should take, would exert all its abilities to merit a place in which consisted for the first time of a soft egg, ll the proposed publication. and one round of toast. Mr. R-- would This monthly course of emulation, in wbich rather that the egg should have been laid by each town would seek to cut a figure, by spara an ostrich than a fowl, but he consoled himself || ing no pains to outdo their rivals, would very in thinking of the toast; he caused the largest speedily bring about a visible amelioration in loaf that could be procured to be bought, so all the productions of the culinary system; that when made it was more than a yard long, poultry would be more carefully fattened. and weighed nearly a pouud. Mrs. R pastry kneaded more scientifically, game more would have interfered but without success, as skilfully selected, and not whether old or be only followed the physician's ordinance. young, tender or tough, indiscriminately put The egg was ushered in with great solemnity, to the spit; pickles and preserves would be and placed on the sick man's bed, who pro more cautiously prepared ; in short, the glory posed himself a great enjoyment; but, fatal of each town and country would be interested misfortuae, he sipped the white with so much that nothing beneath the standard of inedioavidity that he swallowed the yolk! O dire crity should reach the capital; for this perio. calamity, deplorable precipitation, which ren- dical work would exercise on these productions dered the delicious toast completely useless; a criticism as severe, though far moreim parti. and Mrs. R- gravely caused it to be taken al than the Reviews is on every publication, and away with the egg-shell. The despair into Newspapers on our most favourite comedians. No. XXV. Vol. III.