{
    "system": "GoGuides Verified Text",
    "api_version": "verified-text-v1",
    "status": "ok",
    "response_type": "verified_text_record",
    "source_key": "britannica_1926",
    "source_title": "Encyclopaedia Britannica (1926)",
    "license_code": "public_domain",
    "attribution": null,
    "license_url": null,
    "chunk_id": "1926:magnetism terrestrial:d7ed63fb7c09",
    "title": "MAGNETISM, TERRESTRIAL",
    "section": null,
    "hash_alg": "sha256",
    "hash_sha256": "e2c03469f4fe5b49c3445af029e0b845dd6d66358251c34dbbb5d0f86be3cc2c",
    "normalizer": {
        "name": "ggnorm",
        "version": "1.0"
    },
    "verified_text": "further devel- opments occurring in various directions since 1909 in the study of terrestrial magnetism are dealt with below. instruments.—the intercomparison of the magnetic instru- ments of <lifferent countries has a recognised importance. while much was done before the world war by the carnegie institu- tion of washington, the comparisons between adjacent countries, which are specially desirable, have not been numerous. <a diffi- culty increasingly realised is the uncertainty whether any mag- netometer, even if never moved, can be considered invariable to the degree of accuracy usually aimed at, viz., o-1’ in declina- tion (d) and ry (e-o0001 cgs unit) in horizontal force (j/). trouble arises more particularly as regards the collimator magnet’s moment of inertia and the ‘ distribution constants ’’ appearing in the deflection formula 2mr—(1 +pr-?+or *). the use of a coiland an electrical current promises increased accuracy in the measurement of #7, and coil magnetometers have been constructed in several coun- tries, but the accuracy actually attained requires further investiga- tion. a coil instrument for the direct measurement of vertical force (i) would be of great value in high latitudes. surveys.—ohservational work on land and sea has gone on con- tinuously under the auspices of the carnegie institution of washing- ton, and many results have been published. amongst recent sur- veys or resurveys which have been completed, there may be men- tioned those of belgium, the british is., japan and new zealand. there have also been numerous field observations in canada, france, germany, india, the scandinavian countries, spain, the united states of america, and in a number of more restricted areas. eclipse phenomena.—special observations during solar eclipses have been made at many places on a number of occasions, more especially by the carnegie institution of washington, and a good many results have been published in terrestrial magnetism. no consensus of opinion, however, has yet been reached, beyond the fact that any systematic effect ts certainly small. to demonstrate a small systematic cffect would require unusually quiet conditions over a period of days including the eclipse. sudden commencements.—another inquiry depending on co- operation has been into the simultaneity of the so-called ‘‘ sud- den commencements ” (s.cs.) of magnetic storms. it has been suggested by s. chapman and l. rodes that the s.c. might be associated with the engulfing of the earth in a jet or cloud of ions emanating from the sun. if the ionic jet rotated with the sun, as chapman suggests, its time to engulf the earth would be about 30 seconds. if the ionic cloud were stationary, the process would take some 64 minutcs. it seems fairly clear from the several independent investigations which have been made that the differ- ence in the times of s.cs., if any, is a question of seconds, not of minutes. characterisation of days.—since 1906, an international scheme has been in operation with its headquarters at de bilt, nether- 7 cf. a. sommerfeld, op. ctt., p. 384; zetts. fur phystk, vol. 19, p. 221 (1923); ann. der physik, vol. 73, p. 209 (1924); lande, “zeus, fir physik, vol. 15, p. 189, vol. 19, p. 112 (1923); e. c. stoner, foc. cit.; j. w. fisher, foc. czt. 8h]. d, arnold and g. w. elmen, jour. franklin fnst., vol. 195, p- 621 (1923). magnetism, terrestrial lands. each co-operating station assigns to every day a “‘ char- acter ”’ figure o, 1 or 2, according as the day is quict, moderately disturbed or highly disturbed. the arithmetic means of the figures so assigned are given in the annual de bilt lists, so that each day has an international character figure varying from 0-0 to 2-0. intercomparison of the character figures assigned at different stations has confirmed the view that in ordinary lati- tudes disturbance is seldom if ever confined to one area. the de bilt character figures discriminate on the whole very satisfactorily between the days of the same month or season. but there is a natural tendency in the standard represented by 1 or 2 to vary according as the season is more or less quiet. to remove this difficulty, f. bidlingmaier suggested the use of ‘‘ magnetic activity ” defined as the mean value throughout the day of !/sr(e+?+-7’), where a, 8, y represent the departures of the three rectangular magnetic components from their normal values. “ activity ”’ in this sense exists and may be considerable on quiet days. apart from the difficulty of assigning normal values, the amount of labour entailed in the calculation of ‘“‘ activity '\" in the absence of some special mechanical means scems prohibitive. various alternatives have been proposed, including the daily ranges of one or all of the magnetic elements, the squares of the daily or hourly ranges, the variation from day to day in the mean daily value of i, and the number of intersections by the magnetic curve of a series of lines, parallel to the base line. in low latitudes disturbance is largely con- fined to h, and the character of the day may be fairly diagnosed on the zz curve alone, but this is far from the case in high latitudes, twenty-seven-day interval—the existence of the de bilt daily characters has enabled the reality of a 27-day interval in mag- netic disturbance to be investigated without any possible preju- dice. the phenomenon has been found to exist for quiet as well as for disturbed conditions. a day which follows a conspicu- ously disturbed (or quiet) day after an interval of from 26 to 28 days has decidedly more than the average chance of being itself a disturbed (or quiet) day. diurnal variation —the primary object of the international character scheme was the selection for each month of five quict days (commencing at greenwich midnight) from which diurnal inequalities of the magnetic elements should be calculated, either additional to or in place of those derived from all days. of late years five international disturbed days a month have also been selected at de bilt, so that diurnal inequalities may be calculated from them as well. it has been found that in high lati- tudes the diurnal inequality is extremely sensitive to disturbance. this is illustrated by the vector diagrams (see 17.366 and 367) for the horizontal plane in fig. 1. they are for the equinoctial season of rg12 at the two antarctic stations cape evans (77°38' south, 166°24’ east) and cape denison (67°0’ south, 14°40’ east). the curves have been smoothed by the assumption that they are true ellipses, with axes in and perpendicular to the geographical meridian. the hypothesis is certainly not much in error, and it prevents the eye from being distracted by the irregu- larities inevitable in unsmoothed vector diagrams based on a comparatively few days. starting from the centre in each case, the successive curves represent groups of days having for their mean international character figures o-5, 0°15, 0°35, 0-65 and 1:1s. the curves are described in the direction of the arrows, i.e., anticlockwise. magnetic poles—cape evans and cape denison are on op- posite sides of the south magnetic pole. its position is not ex-~ actly known, somewhat conflicting results having been obtained by the different antarctic expeditions. according to e. n. webb in the discussion of the regults of the expedition led by sir doug- las mawson, the approximate position for the epoch 1912 was 71°-2 south, 150°-7 east. thisis considerably to the northeast of the positions assigned by the “ southern cross ” and “ dis- covery ” expeditions (see 17.384). but all the expeditions agree in placing the south magnetic pole near the direct line from cape denison to cape evans. accepting this as a fact, 1t may be shown that a change of 4-sy in the horizontal force vector is roughly equivalent to a shift of 1 km. in the position of the pole. on this basis the curves of fig. 1 constitute independent esti- mates made at the two stations of the daily track of the south magnetic pole, on days of different international character, according to the kilometre scale supplied. the subject has also 795 been investigated for the north magnetic pole for the epoch 1904 by a. graarud and n. russcltvedt, using the observations of amundsen’s expedition. the principal base station, occupied by a magnetograph, gjeahavn, had a dip of 89°17’, and in fixing the position of the pole use was made of four other stations with dips varying from 89°34’ to 89°52’. thus the position found for the north magnetic pole in 1904, viz., 70°30’ north, 95°30’ west, cannot be much in error. this position differs by only 25’ of latitude and 1°16’ of longitude from that assigned in 1831 by james ross (17.384), so there is no suggestion of rapid secular change. on this basis graarud and russeltvedt calculated that a change of . 3-27 in the horizontal force vector answers to a shift of 1 km. in the position of the pole. the curve they give for its daily motion on the average day of 1904 is approximately elliptical, with minor and major axes respectively in and perpendicular to the geographical meridian, the extreme range from east to west ts about 22 km., and that from north to south 13 kilometers. the curve, in short, is very similar to the cape denison curve for character 1-15, though slightly more elliptical. it is described, however, in the clockwise direction, as is natural for the northern hemisphere. the differences in sunspot frequencies, 42-0 in 1904 as against 3:6 in i912, would naturally lead to a considerably larger amplitude in the earlier epoch. z20km, fic. 1.—vector diagrams: (a) cape denison; (b) cape evans. variations of disturbance with latitude —a comparison of the disturbances recorded in 1911-2 at the scott expedition’s ant- arctic station with those at observatories extending from maurit- ius to sitka, alaska, showed a marked tendency for disturbance to be simultaneously great in high northern and southern lati- tudes, and to be less at intermediate stations, whether north or south of the equator. again, comparison of auroras with mag- netic character figures got out for individual hours, as well as for individual days, shows that an intimate relation exists between aurora and magnetic disturbance. while long accepted as true of large magnetic storms and aurora in countries where both phenomena are rare, this seems also true in the case of bright 766 mahaffy—mahan aurora in high latitudes. in the case of faint non-fluctuating | most from truth in the very regions where aurora and magnetic aurora, magnetic conditions seem often practically unaffected. faint aurora, in fact, seems the rule rather than the exception in high latitudes under conditions favourable to its visibility. theory of the regular diurnal variation.—the derivation of the diurnal variation from a potential has been further considered. assuming the derivation possible, the constants occurring in the potential have been calculated by w. van bemmelen, 5. chapman, f. bidlingmaier and j. bartels. a. van vleuten, who has exam- ined the hypothesis critically, especially as applicable to quict-day phenomena, has, however, concluded that the balance of evidence is against it. a difficulty in the way of any general theory of the diurnal variation is the varied influence of disturbance, this in- ' fluence not merely differs at different places, but is not the same for the different elements. it also varies with the season of the year, and is not the same at the same season of different years. general theory.—these various phenomena—the synchronous occurrence of magnetic disturbance in different parts of the earth, its special development in high latitudes, the enhance- ment of the regular diurnal variation during disturbance, the association of disturbance with aurora, and the 27~lay interval —all accord in a gencral way with the theory pretty generally held that magnetic disturbance and aurora are both due to the emission from the sun of some species of electrical radiation. the nature of this radiation, whether 8 or a rays, has been discussed more especially by kr. birkeland, c. st6rmer and l. vegard. difficulties, especially the scattering to be expected from the mutual repulsion of ions, if all of one sign, have been discussed by a. schuster, 8, chapman and f. a. lindemann. when approaching the earth, ions of either sign would naturally spiral round the lines of magnetic force, and so be concentrated in high latitudes. but for ordinary a or 8 rays the approach to the magnetic poles should be closer than auroral phenomena suggest. to explain the occurrence of aurora in comparatively low latitudes, stermer has suggested the existence of a ring of ions in the magnetic equator, but no proof of its existence has been advanced. ‘the presence of ions would naturally increase the electrical conductivity, thus enhancing the amplitude of the regular diurnal variation of the magnetic elements, supposing that due (as is generally believed) to electrical currents in the upper atmosphere. the fact that disturb- ance enhances the diurnal inequality relatively more in winter than in summer would follow naturally from the very probable hypo- thesis that ordinary solar radiation itself increases the conductivity of the atmosphere. in high latitudes we may suppose that in winter the electrical currents associated with aurora play the part which in summer is largely played by direct solar radiation. in the simplified mathematical theory of aurora and magnetic disturbance developed by c. stormer, the earth is treated as mag- netised as it would be if only the first order gaussian harmonic existed. everything is then symmetrical round the axis of the first harmonic, whose north end according to j. c. adams was in 1880 at 78° 24’ north and 68° 4’ west, but moving west through about o°-i per annum. in a theory of magnetic storms, s, chapman also assumes symme- try round an axis, regarded as magnetic latitude go°. he has derived mean results from 40 storms recorded at 12 stations arranged in five groups according to magnetic jatitude. confining himself to storms having an s.c., he regards the “ general storm ” phenomena, 4.e., the phenomena not dependent on local time, as determined by the ‘‘ storm time,” or time elapsed since the s$. c, the phenomena varying with loca) time, he regards as composed of the ordinary diurnal variation 4- a ‘' local storm variation,” determined like the general storm phenomena by the magnetic latitude. ele discusses the electrical current systems supposed to “ flow in more or less horizontal strata in the upper atmosphere ” to which the magnetic changes he has arrived at may be ultimately ascribed. “‘ the external currents will of course be accompanied by carresponding induced currents within the earth which will modify their effects.” taking what he considered an average storm, chapman calculated that it called for the expenditure of energy at the rate of about 2x10! ergs per second for 15 hours. to many minds, theoretical researches of this kind are fas- cinating, but deductions from them, until confirmed by direct observation, are just as hypothetical as the theories themselves. magnetic phenomena are much less simple than theories such as stermer’s and chapman’s suggest. the complete gaussian analysis indicates in reality a considerable departure {rom sym- metry round an axis. high latitudes, moreover, were practically unrepresented in the data used for calculating the gaussian con- stants, while the asymmetry in the positions of the two mag- netic poles suggests that the results of the analysis may depart storms are most developed. the individual aurora or magnetic storm shows no approach to symmetry round a magnetic axis. the magnetic disturbance on & given occasion is of very different amplitude at stations having the same magnetic latitude. even when there is a recognisable s. c. the sequence of events at a given station varies much on different occasions. in low latitudes the s. c. is a change mainly in 77, almost in- variably a rise. in higher latitudes it is usually ascillatory, and may be large in all the elements. the duration of the enhanced value in it following the s. c. is sometimes a few minutes, sometimes several] hours. following the enhancement there is gencrally a pronounced fall, bringing j7 well below its normal value. but the recovery from this depression may sect in after a few hours and proceed almost unin- terruptedly, a return to comparatively quiet conditions occurring within 12 hours, or there nay be a succession of irregular move- ments, highly disturbed conditions lasting for one or two days. the superposition following “ storm time ” of unsorted disturbance curves may give us a storm such as never existed. comparison of magnetic curves from kew, stoneyhurst, eskdajemuir and lerwick has shown that while the amplitude of magnetic disturbance in the british is, almost invariably increases with magnetic latitude, the rate of increase differs widely on different occasions. on special occasions there may be very large rapid movements in lerwick, which are hardly represented in the south of england. the average intensity even of magnetic disturbance must be largely determined by other things than the magnetic latitude, as defined by chapman. agincourt (toronto) and kew are of nearly the same “ magnetic latitude,” but disturbance, at least in 1911-2, was almost invariably much larger at agincourt than at kew. chapman’s estimate of the energy of a magnetic storm is certainly much less improbable than the enormously higher estimate made in 1892 by lord kelvin on the hypothesis of direct magnetic action between the sun and the earth, but it depends fundamentally on several assumptions, the degree of probability of which is at present entirely a matter of opinion. brbllography.—the journal verrestrial afagnetism and aimos- pheric electricity contains original papers and many references. sce also the following:—researches, vols. i to v, carnegic institution of washington, dept. of terrestrial magnetism; c. chree, studies in terrestrial magnetism (1912); daniel l. hazard, directions for magnetic measurements (1911); fe. merlin and o. somville, liste des observatoires afagnetiques, etc. (1910); a. nippoldt, “‘ erdmagnetis- mus’ in miiller-pouillet's lehrbuch der phystk und meteorologie, a4ter band, 5tes buch (1914); a. schmidt, ‘ erdmagnetismus \"’ in encyklopidie d. math. wiss., 6ter band (1917); ‘the scientific papers of the hon. ilenry cavendish, vol. 2, sfagnetic work (1921). lor surveys and results of survey expeditions: a. angot, reseau magnetique de la france et de l’afrique du nord au rer janvier iqrr (1917) and ch. maurain, aum. de i’ pustitut de physique du globe, vol. 2 (1924); c. coleridge farr, afagnetic survey of the dominion of new zealand and some of the oulfying islands for the epoch 3oth june 1903 (1916); a magnetic survey of japan for the epoch 1913 executed by the hydrographic office, bulletin of the hydrographic office, imperial japanese navy, vol. 2 (1918); g. w. walker, “ the magnetic ke- survey of the british isles for the epoch jan. i 1915,” koy. soc. phil. trans., a, vol. 219 (1919) a. hermant, leve alagnuetigue de la belgique au rer janvier 1973 (1920). for expeditions see fr. billing- maicr, kurzensammilung ton erdmagnetischen variationen beobachiet 1902-3 auf der gauss-station im siidlichen eismieey (1912) and fr. bidlingmaier and j. bartels, erdmagnetische variationen— beebach- tungen auf der gauss-station (1923); kr. birkeland, the norwegian aurora polaris expedition, 1902-3 (first section 1908, second section 1913); kurt molin, wissenschaftiiche ergebnisse der schiwedischen sud-polar expedition 1901-3, unter lettung von dr. otto nordenskjald: erdmagnetische ergebnisse (1920); british (terra nova) antarctic expedition rg10o-13: terrestrial magnetism (1921); austratian antarctic expedition ror1-14, under the leadership of sir douglas mawson: scientific reports, \\3, vol. 1, terrestrial magnetism (1925); a. graarud and n. russeltvedt, ‘‘ die erdmagnetischen beobach- tungen der gjea-expedition,” 1903-6, geofysiske publtkationer, vol. 3, no. 8 (1925); bericht ziber die foxtschritte unserer kenntnisse vom magnetismus der ferde (vaii., 1905, bzw. 1913-25) von dr. j. bartels in potsdam. (ce) mahaffy, sir john pentland (1830-19109), irish classical scholar (sce 17.394), became vice-provost of trinity college, dublin, in 1913 and provost in 1914. in recognition of the serv- ices of the college during the world war, he was in 1918 made a g.b.e. from rotr to 1916 he was president of the royal irish academy. he died april 30 10109. mahan, alfred thayer (1840-1914), american naval officer and historian (see 17.394), died in washington, d.c., dec. 1 rorg. his later works included naval strategy compared and contrasted with the principles of militery opcrations on land mah-jongg—mahommedanism (rotr); armaments and arbitration (1912) and the afajor operations of the navies in the war of american independence (19133). see c. carlisle taylor, the life of admiral mahan (1921). mah-jongg.—this is a chinese game, for four players, which was introduced into europe and america about 1923. the game is played with a number of pieces known as tiles. there are 144 tiles in all, comprising four “ flowers,” four “ seasons,” four white, four red and four green “ dragons’’; four each of north south, east and west “ winds”; and three “ suits,’ namely ‘ characters,” “ bamboos ” and “ circles.” each suit consists of 36 tiles, made up of four lots numbered one to nine inclusive. each player plays independently, and the procedure is briefly as follows: the tiles are arranged in pairs face downwards in four sides of a square, each side, or wall, containing 17 pairs. the eight extra tiles are left in the middle of the table to be taken up by any player who draws a “ flower ” or a ‘‘ season.” the bank is allotted by a throw of dice, and the highest throw fixes also the point at which the wall shall be opened. each player is allotted a wind, the banker taking the east wind. each player, starting with the banker and working anti-clockwise, draws four tiles at a time from the wall till each has drawn 12, then the banker draws one extra tile. each player’s object is to make a complete hand of twos, threes, or fours of a kind, e.g., three sixes of ‘characters’ and sequences; orfour, fiveand six of ‘‘bamboos.”’ the actual play commences when the banker discards a tile, placing it face upwards on the table. each player, playing in order clockwise, then draws a tile from the wall and discards one from his hand. should he draw a “ flower” or a ‘‘ season” he exposes it and draws one of the eight extra tiles from the centre of the table. if a player discards a tile of which another player already has two, such other player may cry “ pung’’and take the discarded tile, at once exposing the three tiles on the table. the players on the left of the discarder, by crying “ chow,” may similarly take a discard to complete a sequence of three. a pung or a chow does not affect the order of drawing, nor does it count as a draw. a player punging a tile takes it in preference to a player wishing to chow it. finally, a player requiring a discarded tile to make his hand complete cries mah-jongg, and takes the tile in preference to all other claimants. a player can go mah- jongg either by claiming a discard, or by drawing a tile in the ordinary way, but such tile must complete his hand without further discarding on his part. the hand finishes as soon as one player goes mah-jongg. the scoring is somewhat complicated, and various conditions in a hand entitle the player to double his score. the mah-jongg hand is paid in full by all the others except the banker, who pays him double. if he is himself the banker, he is paid double by all. the other players pay differences to each other, the banker paying or being paid double as the case may be. the bank passes anti-clockwise for the following hand, unless the banker went mah-jongg, when it remains with him. mahler, gustav (1860-1911), austrian composer and con- ductor, was born at kalischt, bohemia, july 7 1860. from 1885 onwards he conducted in prague, budapest, hamburg and london, becoming director of the vienna opera in 1897. by unremitting zeal and tireless enthusiasm he brought the vien- nese opera to a high state of perfection, but the strenuous work which he exacted from all earned him the name of “the tyrant”? and made him many enemies, and in 1907 he was obliged to resign his post. he immediately received the offer of a conductorship in america, which he visited for three seasons, returning to vienna in 1911, where he died on may 18. mahler reflected to some extent in his works the classical tradition inherited from schubert and bruckner. in addition to his songs and chamber music, he wrote no fewer than nine symphonies, planned on a gigantic scale for an orchestra nearly doubled in strength. these lengthy works, though rarely performed, have nevertheless had a certain vogue in holland, chiefly owing to the zeal of the eminent conductor mengelberg. see r. specht, gustav mailer, etc. (1913); p. stefan, gustav mahler, a study 767 of his personality and work (1913); g. adler, gustav mahler (1916); p. bekker, gustav mahler's sinfonien (1921). mahommed v. (mrenmeed) (1844-1918), sultan of turkey, was born at topqapu nov. 3 1844, a younger son of the sultan ‘abdul mejid (1823-1861). he led a quiet and retiring life, and suf- fered at times considerably from the jealousy and suspicion of his elder brother, the sultan ‘abdul hamid ii. on the deposition of ‘abdul hamid he was invested as caliph (may 10 1909). he was, for the most part, merely a tool in the hands of the com- mittee of union and progress and, though he was supposed to dislike the pro-german policy of enver pasha, he was unable to take any effective steps to oppose him. he died at yildiz july 3 1918, and was succeeded by his brother vahid-ed-din (b. 1861) as mamommep vi., the latter resigned in nov. 1922 and died at san remo may 15 1926.",
    "source_url": "https://archive.org/details/encyclopaedia-britannica-encyclopaedia-britannica.-3-encyclopaedia-britannica-inc.-1926",
    "observed_at": "2026-05-17 12:14:12",
    "integrity": {
        "hash_check": "match",
        "hash_scope": "full_normalized_text",
        "computed_sha256": "e2c03469f4fe5b49c3445af029e0b845dd6d66358251c34dbbb5d0f86be3cc2c"
    },
    "machine_use": {
        "read": true,
        "cite": true,
        "decision": "verified_public_domain_text"
    },
    "documentation": {
        "white_paper_url": "https://www.goguides.com/white-paper.php",
        "pdf_url": "https://www.goguides.com/whitepapers/goguides-ai-source-clearance-white-paper.pdf"
    }
}