The Magnetic Survey of the North Pacific Ocean: Instruments, Methods, and Preliminary Results
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ZENODO and vouu .JUNE, 9o6 THE MAGNETIC SURVEY OF THE NORTH PACIFIC OCEAN: INSTRUMENTS, METHODS, AND PRELIMINARY RESULTS. • BY L. A. BAUER, Director. NEED o• OCEaNiC SurvEYS. As is %vellknown, the CarnegieInstitution of Washington authorized its Departmentof Terrestrial Magnetismto undertake a magneticsurvey of the North PacificOcean, and madea pro- visional allotment of $2o,ooo to cover the initial costs of its inau- guration and progressduring the year x9o5,in accordancewith a plan submitted by Messrs. L.A. Bauer and O. W. Littlehales.'-' [The allotmentfor x9o6has beensufficiently enlarged to permit the continuousand uninterrupted prosecutionof the work, and ample assurancehas been received of similar allotments, so that the systematic magnetic survey of the oceanic areas,not alone of the North PacificOcean, is now an assuredfact.] A single quotationwill sufficeto show that there were good groundsfor the undertaking of an oceanicmagnetic survey, and for beginningfirst of all with the Ocean,so rapidlydeveloping in commercial importance--the North Pacific Ocean. ProfessorArthur Schuster states as his opinion' "I believe that no material progressof terrestrial magnetismis possibleuntil the magneticconstants of the great ocean basins,especially the Pacific, have been determined more accuratelythan they are at •Summaryof two addressesbefore the PhilosophicalSociety of Washington, (October,•9o5, and April, z9o6),and beforethe AmericanPhysical Society (in Octo- ber, •9o5), with additions to date. •See Terr. 3fag., Vol. IX, p. •63. x 65 66 L..4. B.4 f_/œR [vo•..x•, No.2.] present. There is reasonto believethat theseconstants may be afi['ectedby considerablesystematic errors. It is possible that these error• have crept in by paying too much attention to measurements made on islands and along the sea coast. •Vhat is wanted are more numerous and more accurate observations on the sea itself." When it is recalled that the oceanic areas embrace nearly three- fourths of the entire surface of the Earth, it is easily understood how preponderatingthe effect of lack of accuratedata over this portionof the globemay be upon the settlementof the greater problemspertaining to the Earth's magnetisnl. To illustrate: it may be recalled that I made a carefully guardedannouncement about three yearsago that the Earth was seeminglylosing its magneticenergy3 This conclusionresulted from careful calculationsbased upon the best magnetic maps avail- able to date. It may further be recalled that later I repeated my computationsof the Earth's magnetic moment or intensity of magnetization,this time dependentupon actually observedquanti- ties on islands and continents, distributed as uniformly over the globe as the distribution of land would permit, and I found that from •89o to •9oo there apparently had occurred a shrinkage of the Earth's magnetic moment at about the same rate per year, as had been deduced from the magnetic charts between I84O and •885,viz., about •4oo part annually. This rate of shrinkage is so large that were it to continue in the same proportion year after year, the Earth would lose half of its present amount of magnet- ism in •66o years.• As stated, this result has been arrived at in two totally different ways, and based each time upon entirely dependent data, and, as far as I know, the methods employed have not been questioned. Yet, the deduction is such a startling one, and, if it be true, will have such an important bearing on problems of terrestrial physics, that it behooves us to be cautious until we can once more verify the matter with the aid of fresh data over the seas as well as on land. Another interesting outcome of my analysis of the Earth's a Terr. ]lœag-.,Vol. VIII, •9o3, pp. 97-m8. • Terr. •1'af., Vol. IX, •9o4, pp. •8•-•86. • This, of course, does not imply that in another •66o years the Earth will have lost all of its magnetism, but merely that in 3,300 years the amount of magnetism •vould be one-fourth that at the present time, etc. permanent magnetic field--one that was certainly not looked for-- was that our knowledgeof the distribution of the Earth's magnet- ism was as well known for the epoch •84o-45 as for the later epoch x885,perhaps even better known, in spite of the fact that magnetic surveys had multiplied, and had been zealously prose- cutedby variouscountries since the earlier epoch.6 I-Iowever, •hese additional surveys applied chiefly to land areas, and not until the recent Antarctic expeditionswere observationsforthcoming from Southern Oceans. It was necessary, therefore, in the construction o[ the 'magnetic charts for x885 to use a great deal of the same material as was used by Sabine in his charts for I84O-45, and to refer it to x885, with the aid of more or less conjectural rates of secular change. This conclusionemphasized forcibly the uselessnessof attempt- ing a re-determination of the magnetic constants of the Earth with the aid of the data at present available, and ! have been informed that an attempt in that direction which had been begun by an eminent foreign magnetician has been abandoned since the announcement of this conclusion. Again, an exhaustive examination of all magnetic data pos- sessedup to date, seemed to poi:nt to the existence of a system of vertical Earth-air electric currents passing from the air into the Earth and v.ice versa, these currents being associatedapparently with the general circulation of the air, so that over the region of the Earth where we have in general upward air currents, as in the equatorial regions, we have an upward flow of positive electricity, and whereth• air currentsproceed in generaldownward, we have a downward stream of positive electricity. 7 This is the deduction from the magnetic data. Students of atmospheric electricity, however, have difficulty in harmonizing the strength of the current deduced with the known electric facts of the atmosphere; though I have been informed by certain inves- tigators that the phenomena of radioactivity and other recently observed phenomena may possibly help in supplying the con- necting link. Be that as it may, the settlement of this question was considered important enough to form the subject of a special resolution at the meeting of the International Association of Academies held in London, May, x9o4. The proposition submitted to the Association by the Berlin • Terr. 2hrag-.,Vol. VIII, p. •27. z See Terr. J/fag., Vol. IX, p. •7. 68 L. A. BAUER [vo•.x•,No.•.] Academy, as the result of a paper by the eminent investigators von Bezold and Schmidt, calledfor a magneticsurvey along a line, or rather a small strip around the entire globe,near the parallel 5ø0 North. If the line integral of the magnetic force taken along this closedcircuit be found equal to zero, the proof of the non-existence of the electric currents above referred to will be proven, at least for that part of the Earth. If, on the other hand, the line integralbe found to have had an appreciablevalue, then conclusionswill result regarding the existenceand direction of the currents. Since sucha line integral must, to a great extent, traverse oceanicareas, it was decidedby the Associationto appointa Com- mittee whichshould first considerthe questionas to the reliability of the determination9f the magneticelements at sea. ThoughI am a memberof this Committee,I am not awarethat anything hasas yet beendone by it. This paper,.however, may be regarded as a first contributionto the settlementof the questionas to the accuracyof magneticdata acquiredat sea. Theseprefatory remarks will serveto presentbriefly the present statusof someof the greaterproblems of the Earth'smagnetism. Theirfinal solution will notbe had until the completionof an ac- curate magnetic survey of the oceans as well as of the land. How- ever great this task of the General MagneticSurvey of the Earth may appear,I have now had sufficientexperience to know that with goodsystem and management,and amplefunds, the work canbe completedin a periodof about fifteen years--the time beingprimarily dependent upon the resources at disposal.[Dur- ing the presentyear, the writer will resignhis officialduties in connectionwith the MagneticSurvey of the United States,now overtwo-thirds completed, in orderto devotehis entireenergies to the directingof this greatertask.] We owe it to the enlightenedinterest of the administratorsof the Carnegiefunds that alreadysufficient encouragement has beengiven to warrantits becominggenerally known that the magneticsurvey of the oceanicareas has at last beenseriously undertakenby an organizationin which confidence can be placed. It is alsogratifying that in additionto the co-operationof the CarnegieInstitution in this greatenterprise, assurance has been receivedof the co-operationand goodwill of the existingfor- eign organizationsengaged in magneticwork. A resolutionto thiseffect was likewise passed at the meetingheld last Septem- Aœ,4G.¾ETIC SUR F•E Y PM CIFIC 0C•,4A7 •9 ber at Innsbruck, Austria, of the International Committee on Terrestrial Magnetism and AtmosphericElectricity, composed chiefly of directorsof meteorologicaland magneticinstitutions. I have said nothing regarding the practicaland eco•mmical importanceof the magneticsurvey of the North PacificOcean, e.g., as applying to the needsof the mariner. Sufficeit to say that no one until now has been able to tell preciselyhow closely the prevailingmagnetic charts could be relied upon. Thus, CaptainCreak, for many yearsSuperintendent of the CompassDepartment of the British Admiralty,now retired,said someyears ago: "The North PacificOcean is, with the exception to the voyage of the Chatlender,nearly a blank as regardsmag- netic observations." My addresswill, in somemeasure, answer this question,and it will be seen that the outcome of this survey has likewise a real economic value. PREVIOUS OCEAlXIIC IVfAGAIETIC SURVEYS. Before passingto the presentocean magnetic survey let us briefly refer to previous work. The firstattempt at an oceanicmagnetic survey was made by the noted astronomer,Edmund Halley, between I697 and •7o•.