MATHEMATICS.

For the Anthologia Hibernica.

THE PHILOSOPHY OF NATURE.

Letter 18th.

On the Nature and Properties of Magnet fm.

(Continued from page 215.)

IF the globe of the earth was homogeneous in every part, there would be a free. communication of the pyrogeneric principle, and ail bodies would be equally magnetic, and reciprocally communicate the principle to each other, as light thro tranfparent fubftances; but from the diverfity of the fpecies of matter, and the different formation of the conftituent parts of bodies, the pyrogeneric principle, though exifting in all, is tranfmitted only through fuch, which contain the greater quantity of the pyrotic element, or what is termed by feveral chemifts, phlogiston, being a proper combination of the pyrogeneric, with the pneumatic principle. Of this element, iron feems of all bodies to be the moft replete, at least in its compact form.

The native load-ftone is a ferrugineous fubftance, containing iron, fulphur, and a great quantity of phlogifton, by which means the pyrotic element pafs and communicate from other bodies freely to it, and from thence tranfmitted in the direction of the pyrotic current. Iron, as containing a greater portion of phlogifton or elementary fire, communicates readily with the load/tone, but in its crude ftate does not become magnetic, and is therefore only attracted by it. But when the phlogifton in the iron is increased, and its pores, which contained heterogeneous matter, closed, the iron being touched by the magnet or loadstone, by communicating freely the pyrotic element, will become magnetical, and attract other ferrugineous

bodies.

The conftituent parts of iron being so difpofed as freely to communicate the pyrotic element, and on communication with the magnet become magnetical, may by fire or fufion be destroyed, and lose all their power.

But iron in any form whatever, if prefented to a magnet or natural loadstone, is inftantly attracted by it; and if the iron be in a metallic form, or, more properly fpeaking, impregnated wiah phlogiston, it will itself become magnetic, and retain property, in proportion as the iron is more or lefs impregnated with the elementary fire; thus, calces of iron, though they are attracted by the magnet, do not become magnetical on coming in contact with it. And iron which contains the

that

VOL. IV. October 1794.

lesf

leaft phlogiston, does not retain the communicated magnetifm fo long as fteel, tho it acquires it more speedily and more ftrongly, for the pores of the metal being more open, the pyrotic element has not a fufficient connection; hence foft steel or iron, receive magnetifm very easily, and lofe it again with equal facility, while hard fteel receives the power with difficulty, but retains it obftinately. Alfo foft iron may be rendered more capable of retaining, magnetism by hammering, as the pores by that means become clofer, and confequently conduct the pyrotic current more regularly.

Iron made red-hot lofes its magnetifm, if it had any, and the hardest steel, while in that state, is little affected by the magnet, for the conflituent particles being in violent agitation by the fire, reject rather than admit the pyrotic element; but on cooling, the phlogifton being in part thrown off by the fire, is readily restored from the magnet, and the power becomes as great as before. Whence magnets or magnetic iron made hot, have lefs power than when cold, and even if heated only by boiling water, do not recover when cold their full power, for water is a great conductor of phlogiston. The decompofition or dephlogiftication of iron by acids, diminish its attraction by the magnet, by depriving it of the elementary fire. But the vitriolic, nitrous and other acids, which contain much phlogiston during their action, encrease the power on the needle.

Every magnet or magnetical iron, whether emitting or immitting the pyrogeneric principle, is furrounded by an effluvia or magnetic atmofphere, which is of two fpecies, affirmative and negative. If the magnetic body is replete with phlogiston, and a free communication is maintained with the pyrotic curve before spoken of, it will emit part of it to the adjacent bodies or air, and have an affirmative atmosphere. But if the magnet communicates freely, but is not replete with phlogiston, or emits it fafter than it receives, the pyrotic element will be immitted from the surrounding bodies, and the magnetic atmosphere will be negative. If two magnets, or magnetical bars of iron, having one an affirmative, the other a negative atmosphere, the pyrotic element, in order to preferve an equilibrium, will communicate, and the magnets will attract each other, with a power proportionate, to the difference of their atmospheres. But if they have both affirmatives, they will repel each other, for the pyrotic element proceeding from each, will act contrary ways, and confe quently endeavour to occupy the place between them, and make them, if moveable, recede from each other. Two negative atmospheres alfo repel, but with this difference, that both immitting the pyrotic element, a current thereof, will rush between them in endeavouring to complete the equilibrium, and make them in like manner recede.

e of

Every magnetic atmosphere has in it, currents of the pyrotic principle, in the direction of the pyrotic curve before mentioned, in which direction alfo, the communication is performed through the magnetic fubftance. Whence all magnets have two poles or points, by which the pyrotic principle is immitted and emitted in the faid direction, according to the confluxing and refluxing state of a curve. Whence, if a bar or piece of iron B (fig. 85) be applied to the fouth pole of magnet A, which immits the pyrotic element, that element will be emitted from the point e the bar B, and confequently the point e will become the north pole of the bar B. And if a bar C be placed at the north pole of the magnet A, which emits the pyrotic element, the point fin C will immit, and confequently become the fame fpecies of pole as b. Whence it is, if a needle be touched by the fouth pole of a loadstone, it will point towards the north, and if touched by the north pole it will point towards the fouth. The confluxing and refluxing ftate of the pyrotic curve on the fame fide of the equator doth not make any difference in the magnetic direction. The magnetic poles of a magnetical iron wire, may be destroyed or even changed; for if a piece of magnetic iron wire be twisted into a ring, the poles act

ing

if

ing contrary will defroy each other, but if the ends are left free and not brought into contact, the communication will be continued and the poles not altered. Alfo an iron wire be touched in the middle by one pole of the magnet, fuppofe the north, that point will become a fouth pole, and the two extremities of the wire, north poles, from the principle before demonftrated. Though the magnetic needle conftantly tends towards the north, it will not be in the direction of the meridian, but in that of the pyrotic curve before defcribed. Whence the magnetic needle will have a periodical variation on each fide of the true meridian, according to the limits before mentioned of the pyrotic curve. To find the time and limits of this variation, we must have recourfe to what has been before faid relative to that fubject.

At Dublin latitude 53° 21' N. the direction is 20° 30', greateft limit 28° 54' and least limit 20°, that the magnetic meridian will vary either eaft or west of the true meridian. In 1657 the needle at Dublin had no variation, but in 1790 2 fpace of 133 years, it had 27° 25' weit, to which, fince 1657, it has been conftantly advancing. Then if we fay as 27.25: 133: 28° : 54: 139 years the term at Dublin, which the needle will take to arrive from the north to its greatest variation weft or eaft: whence the magnetic needle at Dublin will not arrive at its greatest variation weft until the year 1796, nor again point to the north until the year 1935. But if the leffer limit be taken, the term will be only 94 years, whence it would be weft decreasing in 1751, and would again be in the pole in 1846. Having paffed the leaft limit, it may not arrive at the greater, but return in any period between, but which can only be determined by obfervation, and the time is near, when we may expect to fee it accomplished. But before it actually fettles in a decreasing ftate, it probably will vibrate for fome time on each fide of the magnetic meridian.

the

At London lat. 51° 30' in 1657 the magnetic needle had alfo no variation, but in 1753, a period of 96 years, it had 18° 20′ weft, the greatest limit for that lat. being 26° 53', and the leaft 20° 5, whence the period for the greater limit will be 139 years, as before, and the leaft 101. Therefore the magnetic needle at London may have variation weft, decreasing in 1796, and arrive again in the pole in 1935. But the actual period can only be afcertained by obfervation, as the time decreafes from equator towards the poles, under laws which I have not at prefent examined. Though the limits of each latitude are the fame through every degree of longitude, yet the quantity of variation is not the fame in two meridians, as may be observed on infpection of the pyrotic curve, and beyond a quadrant or 45°, on each side of a given meridian the variation will frequently be changed from increafing to decreafing, and the contrary, from meeting with a contrary current, that is, either from the conflux to reflux, or from reflux to conflux. Likewife beyond a femi circle or 90 degrees on each side of a given meridian, the direction will be changed, and what was weft will become eaft, and the contrary, for if weft be the confluxing curve, the opposite hemifphere will have eaft in the refluxing curve, for it is evident that if the curve from the folar vertex v (fig. 83) tend weftward from the equator, the refluxing curve v QP must tend eastward from the fame point. Whence in Europe and the Atlantic ocean, the variation is at prefent weft, but in the opposite hemifphere in the Pacific ocean on the fane fide the equator, it is eaft. fame latitude and longitude on oppofite fides of the equator, will have the direction of their variation changed, from what was weft in one to eaft in the other; though not of the fame quantity. Thus in Europe and the Atlantic, the variation being weft, will in the fame parallel of latitude, and under the fame meridians on the contrary fides of the equator, become eaft, for the pyrotic curves proceeding from the oppofite poles to the equator or folar vertex, will tend in different and contrary directions, as is evident from the nature of the fubject. But beyond the limit of direction

O 2

The

direction or 80°, where the pyrotic curve cuts or touches the equator, the northem and fouthern curves from the oppofite poles, nearly coinciding and forming one continued arch, will have the fame direction of variation, that is, the variation on each fide of the equator under the fame parallels, will be either both weft, or both east, though not of the fame quantity. Whence we find in fouth latitudes from 80° to 142 eaft longitude a weft variation; and it is probable in north latitudes from 80 to 142 weft, the variation is eaft; but thefe being principally in the unknown parts of North America, no obfervation has been made.

Befides this periodical vibration on each fide of the earth's axis or true meridian, there are alfo two vibrations on each fide of the magnetic meridian, the one annual, the other diurnal. The annual is caufed by the change of the folar vertex on each fide of the equator, during the revolution of the earth in its orbit, and whose limits will be in the folftices. The diurnal is caufed by the action of the folar rays on the vertex, during the revolution round the axis in 24 hours. But as these are fmall, and counter-act each other in their refpective periods of a year, and 24 hours, they affect not the general tenor of the variation, but muft be guarded against and corrected in taking obfervations.

Befides thefe variations in the horizontal magnetic needle, there is another which follows the direction of the pyrotic curve within the earth; for if a needle be touched by a natural magnet, it will tend towards a point in the earth's furface, and parallel to the curve before mentioned. Whence fuch direction is called the dipping needle, and is caused by the pyrotic curve not being parallel to the earth's axis; but proceeding from every point thereof towards the folar vertex.

Thus let PCQ (fig. 86) be the earth's axis, P the pole, C the centre, HO the plane of the horizon, A a magnetic body placed thereon, and N the folar vertex. Then will the fection or general direction of the pyrotic curve, from the pole to the vertex, be in the elliptic curve P m V. Whence, instead of the magnetical direction, through the body A being in a, b parallel to the horizontal line HO, it will be in the direction m n. Confequently the angle of the dip will be equal to an angle formed by a line drawn from the pole to the vertex of the place of the body to the folar vertex and plane of the horizon. The method of finding this angle has been fhewn in treating of the pyrotic curve.

A perfect knowledge of the period and quantity both increafing and decreafing of the magnetic variation and angle of the dip, in various latitudes and longitudes, would greatly contribute to the perfection of geography and navigation. But this will require an infinite number of observations, made in places of different long. and lat. during a period of at least 343 years. For which purpose the learned academies in various parts of Europe, ought to inftitute magnetical obfervatories, in which a series of obfervations fhould be continued from age to age, by which the magnetic theory, of which the above is barely an outline, might be completed.

The obferver ought to note down with every experiment of the variation, the date, latitude and longitude, the place of the moon's afcending and defcending node, the proceffion of the equinox, fun's declination, moon's age, nature of the foil at the place of obfervation, the ftate of the atmosphere by the barometer, thermometer, hygrometer, and electrometer. And alfo the time of the day and weather at the time of obfervation, with, as often as poffible, the annual and diurnal librations.

Such a register of annual, quarterly, monthly and occafional diurnal observations, for a number of years, would be of infinite fervice to a commercial nation. The times in which thefe obfervations ought to be more carefully attended to, are at the equinoxes and folftices, the times of the quadratures and fyzigias of the moon's nodes, and on the diurnal and nocturnal meridians. MENTOR.

P. S. The above has been written fome years, and was prepared for the prefs before the author had the pleasure of feeing Mr. Harding's obfervations in the

Anthologia

Anthologia for April laft, and was then furprised to find the theory fo nearly agree with the observation. Mr. Harding found in April 1794, the needle begin to decrease towards the north or east, the theory above gives 1796. But the calculations here have been made in round numbers, without regard to the decimals or correcting equations, as the whole was intended only as a rough outline. If the calculation had been more exact and corrected, it is moft probable the theory and obfervation would have much nearer coincided. But there ftill want many more obfervations to complete the theory, and the prefent decreafe may only be a vibration on the magnetic meridian, before it forms a regular decrease.

SIR,

To the Editor of the Anthologia Hibernica.

AS an admirer of Mathematics and Natural Philofophy, I beg leave, thro' the medium of your excellent Magazine, to communicate a few hints on thefe fubjects to my countrymen.

Waterford,

September 8, 1794.

I am, Sir,

Your most obedient humble fervant,

NICHOLAS WALSH.

IR Ifaac Newton, the glorious idol of the English nation, by his invention of fluxions, and their application to the various branches of mathematics and natural philofophy, raised an emulation in the English which diffused itself through all degrees of age. The oldeft literary characters, which at this bright period were many, applied themfelves with attention to this new ftudy. At this era we may commence the flourishing of the Philofophical Transactions, and behold them teeming with the improvements of men, even in the decline of life, refulting chiefly from this admirable invention. The Encyclopædia, Hutton's Diarian Mifcellany, &c. are proofs of the ardour of the English mathematicians to promote this kind of knowledge. Dean Swift, the idol of the Irish nation, did by no means contribute to the dif feminating of thefe grandeft parts of human knowledge among his countrymen. He treated mathematics and the Newtonian fyftem with contempt, because he knew them not.--He poffeffed in an eminent degree the power of turning his subject to ridicule, and confequently unpreffed the minds of many of his readers with a fixt averfion for fuch ftudies; particularly thofe whofe fuperficial knowledge of thefe sciences precluded them from the happiness of judging for themselves. This, almost national, bias, may account in fome degree for the ignorance of Irish gentlemen in thefe dry and uflefs ftudies, as they term them. The common mode of initiating young men into mathematics, may be another efficient caufe.- Euclid, first put into the hands of the young student, never fails to create a disgust, which can feldom, or never be eradicated. The vast number of theorems to be got by rote, with their formal demonftrations, without the most diftant idea of their application, muit fit extremely heavy on the young memory. -I, with deference to profeffional men, venture to fay, that if the application of plane and fpherical geometry and trigonometry, to the rudiments of geography, navigation, gunnery, fortification, natural philofophy, aftronomy, &c was first taught, then Euclid would become a pleafing concomitant to the gradual progrefs of youth. The confined notion which the generality of the world conceive of the limits of mathematical knowledge, may at least be reckoned one of the fecondary causes of this deep-rooted apathy, which

fome