North magnetic pole

“ On these rocks, we have found orientation changes; that’s why we know the magnetic field have been upside-down and passed through constant changes.
The magnetic north pole changes its exact position in time. Currently, it is nearby Canada and is moving to the Siberian land, located in Russia. Over the last 30 years, the geographic position of the magnetic pole north has changed more than in the previous 90 years. ”

“ The north-seeking end of a magnet is in English-speaking countries called the north pole and the other end the south pole; in France the names are interchanged. If one pole of the bar-magnet is brought near the compass, it will attract the opposite pole of the compass-needle; and the magnetic action will not be sensibly affected by the interposition between the bar and the compass of any substance whatever except iron or other magnetizable metal. The poles of a piece of magnetized steel may be at once distinguished if the two ends are successively presented to the compass ”

“ Well, Benjy, the famous Arctic discoverer, Sir James Ross, in 1832, discovered that the northern magnetic pole was situated in the island of Boothia Felix, in latitude 70 degrees 5 seconds and longitude 96 degrees 46 seconds West. It was discovered by means of an instrument called the dipping needle, which is just a magnetised needle made for dipping perpendicularly instead of going round horizontally like the mariner’s compass. A graduated arc is fitted to it so that the amount of dip at any place on the earth’s surface can be ascertained. ”

“ If we look away from the actual condition of the earth and take the question in its generality, there may certainly exist more than two magnetic poles; but it does not appear to have been noticed that if, for example, two north poles exist, there must necessarily be between them yet a third point, which is likewise a magnetic pole, but is properly neither a north nor a south pole, or is both if that expression be preferred. ”

“ If a magnetized needle were supported so that it could move freely about its centre of gravity it would not generally settle with its axis in a horizontal position, but would come to rest with its north-seeking pole either higher or lower than its centre. For the practical observation of this phenomenon it is usual to employ a needle which can turn freely in the plane of the magnetic meridian upon a horizontal axis passing through the centre of gravity of the needle. The angle which the magnetic axis makes with the plane of the horizon is called the inclination or dip. ”

“ We must expect a considerably greater displacement of the position of the southern pole. At Hobart Town, which is the nearest station to this pole, calculation gives too low a dip by 3° 38′, as far as the observation can be depended upon. It seems probable, therefore, that the actual south magnetic pole is considerably to the north of the position given by our calculation ”

“ In our present explorations we have got so far beyond the beaten track of travel that greater allowance than usual has to be made. In fact we have got considerably to the north of the magnetic pole. At the same time we are a good way to the east’ard of it, so that when I see the compass with its letter N pointing to what I know to be the magnetic north, I take our geographical position into account and steer almost due east by compass, for the purpose of advancing due north. ”

“ Unless the diurnal inequality vanishes in its neighbourhood, a somewhat improbable contingency considering the large range at the “Discovery’s” winter quarters, the position of the south magnetic pole has probably a diurnal oscillation, with an average amplitude of several miles, and there is not unlikely a larger annual oscillation. Thus even apart from secular change, no single spot of the earth’s surface can probably claim to be a magnetic pole in the sense popularly ascribed to the term. ”

“ The Æthiopian magnets if they be powerful, like those brought from China, because all strong ones show the effect more quickly and more plainly, attract more strongly in the parts nearest the pole, and turn about until pole looks directly at pole. The pole of a stone more persistently attracts and more rapidly seizes the corresponding part (which they term the adverse part) of another stone; for instance, North pulls South; just so it also summons iron with more vehemence, and the iron cleaves to it more firmly whether it have been previously excited by the magnet, or is untouched. ”

“ Sir James Ross claimed to have discovered the magnetic pole at about seventy-four degrees latitude. This is wrong—the magnetic pole is exactly one-half the distance through the earth's crust. Thus, if the earth's crust is three hundred miles in thickness, which is the distance I estimate it to be, then the magnetic pole is undoubtedly one hundred and fifty miles below the surface of the earth, it matters not where the test is made. And at this particular point one hundred and fifty miles below the surface, gravity ceases, becomes neutralized ”

“ It has poles, not mathematical points, but natural termini of force excelling in primary efficiency by the co-operation of the whole: and there are poles in like manner in the earth which our forefathers sought ever in the sky: it has an æquator, a natural dividing line between the two poles, just as the earth has: for of all lines drawn by the mathematicians on the terrestrial globe, the æquator is the natural boundary, and is not, as will hereafter appear, merely a mathematical circle. It, like the earth, acquires Direction and stability toward North and South, as the earth does ”

“ The north pole of the weak magnet points in the same direction as those of the strong ones, but since it is in contact with the south pole of a stronger magnet, there is an excess of south magnetism in the neighbourhood of its north pole, which causes the small magnet to appear oppositely magnetized. ”

“ Unless the path of the induction is entirely inside the metal, free magnetic poles are developed at those parts of the metal where induction enters and leaves, the polarity being south at the entry and north at the exit of the flux. These free poles produce a magnetic field which is superposed upon that arising from other sources. The resultant magnetic field, therefore, is compounded of two fields, the one being due to the poles, and the other to the external causes which would be operative in the absence of the magnetized metal. ”

“ Further observations in circles round about the approximate point of each magnetic pole would add very much to our knowledge of terrestrial magnetism.
Terrestrial magnetism is altogether a most intricate and difficult science, but it is perfectly obvious that one very great use of an intimate study of this subject is for purposes of navigation. In the days of sailing ships, the finest course that was laid till recent years was to a quarter of a point or nearly three degrees of the circle, nowadays no steamer of any importance steers a wider course than one degree. ”

“ It further appears that the magnetic force is not evenly distributed on the earth, and that the points of maximum intensity do not coincide with either of the magnetic poles. In the northern hemisphere there are two foci of maximum force of unequal intensity, the most powerful lying at about latitude 53° north, longitude 92° west, near the great American lakes, the weaker in latitude 65° north, longitude 115° east, in Siberia. ”

“ The difficulty was overcome by C. A. Coulomb, who by using very long and thin magnets, so arranged that the action of their distant poles was negligible, succeeded in establishing the law, which has since been confirmed by more accurate methods, that the force of attraction or repulsion exerted between two magnetic poles varies inversely as the square of the distance between them. Since the poles of different magnets differ in strength, it is important to agree upon a definite unit or standard of reference in terms of which the strength of a pole may be numerically specified. ”