a history of the early recording of geomagnetic variations

A history of the early recording of geomagnetic variations

Wilfried SchroÈ der*, Karl-Heinrich Wiederkehr

Geophysical Station, Hechelstrasse 8, D-28777 Bremen-Roennebeck, Germany

Received 26 August 1999; received in revised form 15 November 1999; accepted 17 November 1999

Abstract

As pulsations and circulating currents are caused by solar activity, a short survey is given of how to recognisesolar in¯uences on terrestrial magnetism, and particularly the hypotheses of Balfour Stewart and the two treatises ofArthur Schuster about the daily variations. In meteorology and geomagnetism, photographic self-registering

equipment was developed in Greenwich and Kew; E. Mascart and M. Eschenhagen continued this line. With thehelp of his ``FeinregistriergeraÈ t'' (quick-run magnetograph) Eschenhagen could for the ®rst time record pulsationsmore precisely. Through short-time simultaneous observations suggested by him, the course of a terrestrial magneticdisturbance could be pursued. This disturbance was identi®ed by A. Schmidt in 1899 as a moving circulating current

in the upper layer of the atmosphere. 7 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Pulsations; Circulating currents; Photographic self-registering equipment; Solar activity; Geomagnetism

1. Introduction

The so-called ``pulsations'' Ð oscillatory disturb-ances of very small magnitude Ð are one of the mostcurious variations of the geomagnetic ®eld. Their peri-

odic time ranges from 0.2 s (``micro-pulsations'') to 10min (``macro-pulsations''). The pulsating variations ofthe magnetic needle had already been noticed several

times before 1896 Ð by Johann von Lamont(1841,1851), Balfour Stewart (1859,1861) and FriedrichKohlrausch (1882,1897). The ®rst actual recording,

however, was achieved by Max Eschenhagen (1858±1901), with his quick run magnetograph. Eschenhagenand his associate, Arendt (1860±1920), supposed fromthe start that electrical activity in the atmosphere was

responsible, and they thought that they saw in this ahitherto undiscovered solar±terrestrial phenomenon.This study will seek to show how an occurrence of

such relative brevity could be recorded with the aid ofa magnetograph, and to this end we shall examine the

history of the development of these self-activatingphotographic devices.

2. The discovery of solar±terrestrial interrelations

Gauss put forward his ``Theory of Terrestrial Mag-netism'' in 1838. It was not a theory in the usual sense,but rather a mathematical interpretation of the mag-netic ®eld, with the aid of potential theory, without,

however, actually establishing the underlying causes ofterrestrial magnetism. He also considered the possi-bility that variations or disturbances could be caused

by electrical currents in the atmosphere (Gauss, 1839).Even during the existence of the ``GoÈ ttinger Magne-tischer Verein'' (the ``Goettingen Magnetic Union''),

under the leadership of its three bright stars Ð Alex-ander von Humboldt (1769±1859), Carl Friedrich

Journal of Atmospheric and Solar-Terrestrial Physics 62 (2000) 323±334

1364-6826/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.

PII: S1364-6826(99 )00100-5

* Corresponding author.

Gauss (1777±1855) and Wilhelm Weber (1804±1891)Ð international cooperation grew up systematically.

The chief initiators of this bold enterprise were JohnF.W. Herschel (1792±1871) and Edward Sabine (1788±1883). The ®nest fruit of many years of work at the

observatories in England and the colonies was Sabine'sdiscovery of the parallel between the sunspot cycle andthe mean intensity of magnetic disturbance (Sabine,

1852). Even though Sabine's discovery Ð or rather hisassertion Ð was somewhat questionable, he soonreceived support from Hermann Fritz (1830±1893) (see

SchroÈ der, 1974, 1984, 1999). Starting in the 1860s, thisscientist, who worked at the Technical High School inZuÈ rich, had occupied himself intensively with thephenomenon of auroras. He came to the conclusion

that here likewise a parallel existed between the fre-quency of appearance of auroras and the incidence ofsunspot groups, the cycle having a period of some 11

years. Before Fritz's viewpoint was generally accepted,however, some more years were yet to pass.At Kew and Greenwich, in 1859, an occurrence was

observed that would have caused a sensation, if only ithad been properly recognized and not misinterpreted.An astronomer at Greenwich, Richard Carrington

(1826±1875), had just recorded a group of sunspots,when two bright white spots appeared amongst themÐ a phenomenon never observed previously. We knowthis today as a ``solar ¯are''. A few hours later there

appeared on the magnetogram at Kew evidence of amagnetic disturbance. The observatory possessed atthat time automatic photographic magnetometers.

Eighteen hours later a magnetic storm erupted, as wasshown by the recording of violent disturbances (Bar-tels, 1937). Today we know that, initially, X-rays

emerged from the bright white spots, e�ectivelystrengthening the electrical currents in the ionosphere.During this process corpuscular radiation was alsoexpelled from the Sun. Moving at a slower speed than

light this precipitated a magnetic storm when itreached the Earth. Leading physicists, however, LordKelvin amongst them, saw in this concurrence of

events only ``a manifestation of pure chance''.

3. The construction of early versions of self-activating

photographic recording devices at Greenwich and Kew

Let us now turn to the history of the automaticrecording devices, which made continuous observationpossible and played such an important part in develop-

ing our understanding of solar±terrestrial e�ects. Thediscoveries of Louis Jacques MandeÂ Daguerre (1787±1851), Daguerrotype photography, and William Henry

Fox Talbot (1800±1877), silver chloride paper, hadalready by 1839 been adopted for scienti®c use inmeteorology and geomagnetism. For magnetometers,

where the forces involved were too small to be regis-tered by any mechanical means, these photographic in-

novations o�ered an ideal solution. BetweenGreenwich and Kew Observatories a contest arosefrom the 1840s onwards to determine the best methods

of recording and the best instruments to use. Oneshould note, however, that even shortly before thistime one T.B. Jordan, instrument maker to the Royal

Cornwall Polytechnic Society, had already built self-activating meteorological and magnetic instruments(see SuÈ ring, 1911). At the beginning of the 1840s, the

old astronomical observatory in Kew, near Richmondin Surrey, had been changed into an observatory forthe study of magnetism and meteorology. Its ®rstSuperintendent was Francis Ronalds (1788±1873). In

1852, John Welsh (1824±1859) took his place, in 1859,Balfour Stewart (1828±1887), then in 1871, SamuelJe�ery and in 1876, George M. Whipple (1842±1893).

Ronalds constructed photographic recording magnet-ometers and meteorographs of widely-varying design(Ronalds, 1847). In 1857, the London instrument

maker, Patrick Adie, produced improved models tospeci®cations prepared by Welsh. These ``Kew Magne-tographs'' as they were called were acquired by numer-

ous observatories worldwide, including Potsdam (seeScott, 1885). The recording process was successful,using photo-sensitive waxed sheets, in accordance withthe system of ``Le-Gray-Crookes''. Edward Sabine and

Balfour Stewart con®rmed their e�ectiveness, using themagnetograms in a large number of studies. At Green-wich likewise Charles Brooke (1804±1879) had since

1846 been making self-activating meteorological andmagnetic instruments and these were also adopted by anumber of other observatories (Fig. 1) (Brooke, 1846).

Their design principles signi®cantly outclassed those ofAdie: Brooke made early use of silver bromide paper.Not until 1882, however, did silver bromide gelatinepaper become generally available for purchase (Gor-

don, 1883).

4. The Potsdam Adie-apparatus in Wilhelmshaven

The equipment acquired by Potsdam was installed inGermany for the ®rst time during the First Polar Year,1882±1883, at the Imperial Naval Observatory in Wil-helmshaven. The Gauss Observatory of GoÈ ttingen, a

place of high esteem under the leadership of ErnstSchering (1824±1889), had, after the Austro-PrussianWar of 1866, been neglected ®nancially by the Berlin

administration, the Kingdom of Hannover havingbeen, as an ally of Austria, on the losing side. TheObservatory at Bogenhausen, near Munich, was

obliged under Lamont's successor to abandon its geo-magnetic work because of electrical interference fromthe nearby city. Thus, Germany's principal station in

W. SchroÈder, K.-H. Wiederkehr / Journal of Atmospheric and Solar-Terrestrial Physics 62 (2000) 323±334324

the First Polar Year was Wilhelmshaven, and the

Naval Observatory there occupied a senior positionuntil in 1890 the newly founded Potsdam Geomagnetic

Observatory took over its activities. The Naval Obser-

vatory had been established in the 1870s, with the taskof providing, for the aspiring German Navy, infor-

mation about geophysical matters Ð tidal estimates,

horological determinations, meteorological data andothers. Here also was a new location for the study of

geomagnetism. Thanks to the urging of Georg Neu-mayer (1826±1909, he was ennobled in 1900), in his

role as Director of the German Naval Observatory of

Hamburg (Deutsche Seewarte in Hamburg), the KewPattern Magnetometer owned by the Astro-Physical

Observatory was relocated on loan at Wilhelmshaven.

Neumayer had been one of the initiators of thePolar Year, as was the Austrian naval o�cer and

Polar explorer, Carl Weyprecht (1838±1881). Neu-

mayer was on friendly terms with Carl BoÈ rgen (1843±1909), Director of the Wilhelmshaven Naval Observa-

tory, and shared scienti®c work with him (cf. SchroÈ der

and Wiederkehr, 1992a, 1992b).During the installation of the Adie-Pattern auto-

matic photographic devices an unexpected di�culty

arose (Fig. 2). At Kew gaslight was available, but inWilhelmshaven they only had kerosene lamps, which

gave a too dim light. Success was only achieved with

the emergence for sale of the newly developed silver

bromide gelatine paper. In a report of 3 January 1883,

written by BoÈ rgen to Neumayer, he says (unpublished

source):

Die Resultate [mit dem Bromsilber-Gelatine-Papier]

waren uÈ berraschend gut, waÈ hrend bei dem Wach-

spapierverfahren sich auf ziemlich dunklem Grunde

eine nur wenig dunkle Linie zeigt, war hier eine

tiefschwarze Linie auf hellem, fast weissem Grunde

sichtbar, welche sich mit groÈ sster Genauigkeit able-

sen laÈ sst, und es kommen auch sehr schnelle Bewe-

gungen der Nadeln, bei denen jeder Punkt des

Papiers hoÈ chstens 5±10 Sekunden oder noch weni-

ger exponirt sein kann, vollkommen scharf zur

Erscheinung. Dies hat sich vor allem bei den enor-

men StoÈ rungen am 17±21 Novbr. gezeigt.

The results [with the silver bromide gelatine paper]

were surprisingly good. Whereas with the waxed

paper only a pale, indistinct line shows against a

darkish background, here we see a solid black line

on a bright, almost white, ground, which we can

read with the greatest accuracy. Also revealed are

very rapid needle-movements whose every detail

shows with complete sharpness after an exposure-

time of 5 to 10 s or less. This had been most evi-

dent during the extremely violent disturbances of

the 17 to 21 November.

Fig. 1. Charles Brooke's Apparatus. On the left, the Declinometer; right, the Bi®lar-Magnetometer, for determining the horizontal

intensity. The circular mirrors are divided into two parts, the lower half recording the baseline. Centre is the drum with the photo-

sensitive paper, and beside it the gas-lamps.

W. SchroÈder, K.-H. Wiederkehr / Journal of Atmospheric and Solar-Terrestrial Physics 62 (2000) 323±334 325

Copies were made of the magnetograms, using theblueprint process, and distributed to the International

Polar Commission, and to other observatories. On thescore of expenses, the kerosene, the silver bromidegelatine paper, chemicals for developing and ®xing,

and the so-called ``Steinbach paper'' for the blueprintprocess were the dearest materials. However, to accom-modate all the apparatus for measuring the geomag-

netic variations, they had to provide at Wilhelmshavena special building, set several metres deep in theground, like an ``ice-house'', with double walling and

an air-lock entrance, all designed to maintain a con-stant temperature within (cf. Neumayer and BoÈ rgen,1886).

5. Max Eschenhagen becomes ``Geomagnetican'' at the

Naval Observatory

The supervision of the data recording, and the pro-duction of duplicated copies lay mainly in the hands of

Max Eschenhagen (Fig. 3). Originally he had wantedto become a teacher in higher education. He had stu-died mathematics and natural sciences at Halle (Saale),

taking a Doctorate in physics, and hoped then tosecure a position in Hamburg, a city keenly intent on

economic growth. On 1 February 1883, he came to theGerman Polar Commission in Wilhelmshaven, as an

assistant, substituting initially for the Secretary, whohad fallen ill. He worked his way so well into all thesenew areas that BoÈ rgen soon found him indispensable.

When the Polar Year ended he was entrusted with theconsolidation and evaluation of all the geomagneticdata accumulated at Wilhelmshaven and gleaned also

from the two German Polar Expeditions, the Northernone to Kingua Fiord and the Southern to South Geor-gia. All this he accomplished, investing his work with

illuminating clarity and critical perception; he felt him-self inspired, moreover, to embark on studies of hisown, which later on became of considerable import-ance to him (Eschenhagen, 1896). Eschenhagen also

made a start during those years on a geomagnetic sur-vey of North Germany. He gained much experience inusing the recording equipment, and was able later on

to develop an improved model (Eschenhagen, 1882;1883).

6. Eschenhagen's summoning to Potsdam, and the ®rst

accurate recording of pulsations

The long-anticipated reorganisation Ð or rather the

Fig. 2. Magnetograph by Patrick Adie (Kew Pattern). In the octagonal wooden container, with lid, are the drums and the clock

mechanism. The light-beams emerge from the instruments through wooden tubes. On the left stands the Bi®lar; centre, but not vis-

ible, is the Lloyd's balance magnetometer, measuring the vertical intensity and its variations; right is the Uni®lar, measuring decli-

nation. In front of each instrument a gas-lamp. One could also observe with the eye, using telescopes and measuring-scales. All

three instruments are enclosed in glass vessels pumped free of air.


extension Ð of the small Meteorological Institute inBerlin ®nally began in 1885 with the appointment of

Wilhelm von Bezold (1837±1907). Upon the ``Telegra-phenberg'' at Potsdam Ð ``Telegraph Hill'' Ð a wholecomplex of scienti®c observatories was established. The

Observatory for Geomagnetism was situated quiteclose to the Observatory for Astrophysics. Amongst itstasks was that of observing activity on the Sun. The

building of the Geomagnetic Observatory had alreadybegun by 1887. Its design followed that of the observa-tory built in 1883 in the Parc St. Maur near Paris, to

plans devised by Elie Mascart (1837±1908) (Fig. 4).Already during the First Polar Year the French hadmade use of self-activating photographic magneto-graphs, during their Southern expedition to Cape

Horn (cf. Mascart, 1900). The Paris ®rm of Carpentierbuilt the instruments to plans by Mascart. They werequite di�erent from those of the Kew pattern, mainly

in the way in which they recorded. To serve the threemeasuring instruments Ð declinometer, bi®lar magnet-

ometer and Lloyd's balance magnetometer Ð Mascartused only a single light source: it was a type of lantern

attached to the recording cabinet that contained theclock and the roller-drive mechanism. Potsdamacquired some of the Mascart-type magnetometers

(Fig. 5). They had relatively small magnets, and sothey proved useful for observing rapid changes in thegeomagnetic force. Because of their sensitivity, es-

pecially in respect of temperature deviations, thesedevices, used to measure the variations, were housed inan underground chamber (Eschenhagen, 1894). In

Fig. 4. Elie Mascart's recording apparaturs (from the ``TraiteÂ

de Magnetisme Terrestre'', p. 203). The photo-sensitive paper

was positioned to move downwards at a uniform speed

between two glass plates, of which the rear one was black-

ened. The lantern, set above on the cabinet, had three tubes

leading from it, with apertures for light to pass. Total-re¯ec-

tive prisms (P shows one of these) guided the light rays

through a slit onto the photographic paper.Fig. 3. Max Eschenhagen (1858±1901).


1889, Eschenhagen was summoned to Potsdam; W.

von Bezold wrote (von Bezold, 1902):

Als es sich darum handelte, einen Leiter fuÈ r das

neue Observatorium zu ®nden, konnte die Wahl auf

keinen anderen als Eschenhagen fallen, der sich mit

solchem Nachdruck und so schoÈ nen Erfolgen auf

die erdmagnetischen Studien verlegt hatte.

When we came to consider ®nding a Director for

the new Observatory, our choice could be no other

than Eschenhagen, who had devoted himself with

such energy and such splendid success to the study

of geomagnetism.

For making photographic recordings Eschenhagen

constructed his own instrument, drawing upon his ex-

perience with the Kew Pattern at Wilhelmhaven. His

so-called ``Potsdam Model'' again used drums, which

carried the photo-sensitive paper. In Fig. 6, only three

drums can be seen, the fourth drum having been

detached, so as to give a better view of the others. It

served usually as a reserve, or for a di�erent type of

observation Ð for example, of ``earth-currents''

(Eschenhagen, 1894).In 1896, Eschenhagen arranged for the ®rm of O.

Toepfer in Berlin to build a more handy, easily

transportable, recording device to these same prin-ciples. The drums could be so adjusted that theycould not only make one revolution in 24 h, but

also in 1 h. Thus, one could record very muchmore rapid and transitory happenings. With this``FeinregistriergeraÈ t'' (``®ne-recording, quick-run-mag-

netograph'') Eschenhagen (1896) now discovered``the geomagnetic elementary waves''. As soonbecame clear, however, this kind of rapid periodic

oscillation had already been observed previously.Indeed from 1890 these disturbances had beenappearing in a somewhat indistinct, smeary manneron the Potsdam recordings, made at more ordinary

recording speeds. In July 1896, von Bezold pre-sented Eschenhagen's ®rst short report to the BerlinAcademy of Sciences. One year later there followed

his more comprehensive treatise ``UÈ ber schnelle, per-iodische VeraÈ nderungen des Erdmagnetismus vonsehr kleiner Amplitude'' (On the rapid, periodic

changes of very small amplitude in the Earth's mag-

Fig. 5. The underground room at Potsdam, with the equipment for measuring variations Ð the ``Hauptsystem'' (``main system'').

Centre: the photographic recording device (Eschenhagen's pattern); Right; the declinometer; Left: the bi®lar; Background: the

Lloyd's balance. As well as this so-called ``Hauptsystem'' there was also a ``Kontrollsystem'' (``control system''), with other types

of instruments, for observing with the eye.


netic ®eld). These tiny oscillations, recorded with a

period of oscillation of 12 s, must in Eschenhagen'sopinion be the briefest of all; for this reason hecalled them `Èlementarwellen'' (`èlementary

waves''); they are superimposed on greater disturb-ances. As for their cause, it was thought from thestart at Potsdam that electrical currents in the at-

mosphere were responsible. A fellow-scientist, Theo-dor Arendt, had been occupied since 1890 withthese phenomena, discernible even then in the stan-

dard type of magnetogram. He sought to relatethem to atmospheric electrical activity, thunder andlightning, but could not prove it (cf. Arendt, 1896).

The name chosen by Eschenhagen `èlementarywaves'', is perhaps somewhat too pretentious. The

Dutch geomagnetican, Willem van Bemmelen (1868±

1941), worked in Batavia (now Indonesia), whichlies at a latitude where there is little geomagneticdisturbance; he too devoted himself to the study of

these rapid periodic oscillations, and in 1899 hereferred to them more appropriately as ``pulsations''(van Bemmelen, 1899).

To investigate the extent of this phenomenon,Eschenhagen arranged as early as 1895 simultaneousobserving at Potsdam and Wilhelmshaven, and so as

to examine generally the exact duration and shape of amagnetic disturbance, simultaneous observation timeswere planned on 4 days in February and March 1896,

when 15 observatories spread around the entire worldwould participate (Eschenhagen, 1898). Contrary to

Fig. 6. M. Eschenhagen's recording device (``Potsdam Model'', 1890). In front of each drum, carrying the photo-sensitive paper,

stands a cylindrical lens which concentrates the light-beams into a point. The tubular-shaped part contains a benzene-lamp to illu-

minate the apertures. In this picture the lamp has been raised and the little access-door opened. The clock mechanism operates an

automatic timing device, which, by a process of dimming the light, records time-markings on the base-lines. The whole instrument

was made by the Berlin craftsman J. Wanscha�. To cope with unusualy large de¯ections of the light-pointer these instruments were

®tted with a three-part facetted mirror, so that the light-trace could be held clear and steady even during pronounced disturbances.


Arendt's view Eschenhagen believed that the cause (itcould naturally only be an hypothesis) was to be

sought in the outer regions of the atmosphere. In histreatise of 1897 he wrote:

Erinnern wir uns, daû fuÈ r die groûen Wellen dertaÈ glichen Periode nach Darlegungen [von ArthurSchuster]...., soweit das jetzige Beobachtungsmater-ial den Nachweis gestattet, der Ursprung in den

allerhoÈ chsten Schichten der AtmosphaÈ re zu suchenist, so ist wohl denkbar, dass diese kleinen Wellenebenfalls dort ihren Ausgang nehmen, wofern nicht

besondere VorgaÈ nge auf der Sonne die ersten Ursa-chen bilden.

We should remember that the origin of the major

¯uctuations, with their daily periodic movement, isto be sought in the uppermost levels of the atmos-phere Ð according to Arthur Schuster's claim, and

always providing we can draw proof from theobservational knowledge at present available to us.So might not one also consider whether these tiny

variations may also have their origin up there Ðunless they are ®rst caused by special activity onthe Sun itself.

7. Studies by B. Stewart and A. Schuster: a new

dimension in solar±terrestrial relationships

Because Eschenhagen referred to Schuster's theoryand suggested similar causes for pulsations, perhapswe should look brie¯y at the pioneering work of Bal-four Stewart and Arthur Schuster (1851±1934). Balfour

Stewart was the ®rst to put forward the idea of a re-lationship between everyday sunshine and geomagneticphenomena. Most scienti®c historians date this to

1882, and cite an article by Stewart published in the`Èncyclopaedia Britannica'' (Stewart, 1883). But Stew-art had already advanced this thesis in the ``Proceed-

ings of the Royal Society of London'' between 1877and 1879. In his article `Òn the variations of the dailyrange of the magnetic declination as recorded at KewObservatory'' he wrote (Stewart, 1878):

I would next remark that the hypothesis asserting aconnection of some kind between magnetical and

meteorological phenomena appears to be borne outby the results of this paper.

Stewart also takes care to point out in a footnote that

``Mr. Baxendell of Manchester'' had already beforehim suggested that a link could well exist between aircurrents and the daily changes in magnetic declination.

In the ``BeiblaÈ tter zu den Annalen der Physik und Che-

mie'' (1880), one ®nds a resumeÂ by Stewart (in Germantranslation evidently by Eilhard Wiedemann), with thetitle: `Èine Hypothese zur weiteren Erforschung der

Meteorologie und des Erdmagnetismus'' (`À hypoth-esis towards the further exploration of meteorologyand geomagnetism''). In this the Earth and the atmos-

phere are compared to a ``RuÈ hmkor�'s induction-coil''. The Earth represents the iron core of the induc-

tor, and the outer, rare®ed layers of the atmosphererepresent the secondary coil. Sudden changes in terres-trial magnetism cause induction currents in the second-

ary coil. Similarly, the electric currents in theatmosphere would have an e�ect upon the electrically

conducting layers of the Earth. Stewart was thinkinghere of the polar light, whose cause, as he saw it, laywithin the Earth. Kristian Birkeland (1867±1917) and

Carl StoÈ rmer (1864±1957) were the ®rst to propoundthe theory in 1899 and 1900 of electronic emissionfrom the Sun. The existence of the electron had been

®rst shown in 1897 by J.J. Thomson.Stewart also compared the Earth in his compilation

with an `èlectromagnetic machine'' (an electric genera-tor). Thus the ``dynamo theory'' was born. The upperlayers of the atmosphere move, according to Stewart,

through the lines of force of the geomagnetic ®eld.Since these upper, rare®ed regions possess, as Faraday

indicated, electrical conductivity, they have electric cur-rents induced in them, just as in the rotor of adynamo. As they follow the Sun's movement each day,

these upper strata of the atmosphere expand, and thenlater contract, in response to changes in temperatureand pressure. Stewart believed that in this could lie the

cause of the daily variations in the Earth's magnetic®eld.

These daily variations in terrestrial magnetism hadoccupied Christopher Hansteen (1784±1873) since1819. He sought to ascribe them to an action at a dis-

tance from the Sun. After the discovery of thermoelec-tricity (1820) scientists tried to relate the daily and

seasonal changes in the Earth's magnetism to the vary-ing levels of heat received from the Sun. Faradaybelieved that he had found the cause in the powerful

paramagnetism of the oxygen in the air and the vary-ing temperature of the atmosphere. All these hypoth-eses failed to hold out against the weight of objections

and con¯icting calculations. More success seemedlikely for Stewart's idea of the inductive e�ect of the

geomagnetic vertical component upon agitated conduc-tive layers of air. Schuster now added quantitative con-siderations in support of this view. Schuster made a

two-fold contribution (cf. Schmidt, 1917). In the studyof 1886 he showed that the ®eld of variation actuallyobserved consists of two parts Ð an external and in-

ternal part, the latter caused by the rotating Earth(Fig. 7) (see Schuster, 1886).


He based this claim on Gauss' ``Allgemeine Theorie

des Erdmagnetismus'' (1838), according to which one

can decide by the analysis of spherical functions,

whether the causes lie within the solid ground or out-

side it. In his second study (1889), Schuster used Stew-

art's hypothesis to explain periodic daily variations

(see Schuster, 1889). Physicists in those times had little

of the basic knowledge needed to assume (or rather to

accept the hypothesis) that electric currents pervaded

the upper atmosphere. Robert von Helmholtz (1862±

1889) had already struggled with dissociation in air

and other gases (1889), and was inclined to agree with

the view of his father, Hermann von Helmholtz, as

expressed in the famous Faraday lecture (1881), that

the ions of gases were the carriers of elementary elec-

trical charges (see SchroÈ der and Wiederkehr, 1997).

Wilhelm Hallwachs (1859±1922) announced in 1888

that in the e�ect now named after him it seemed that

particles of electricity were released from metals by the

action of ultra-violet light. Julius Elster (1854±1920)

and Hans Geitel (1855±1923) demonstrated around

1890 that electric conduction could take place by

means of ions. They also recognized, however, that the

photoelectric e�ect, initiated by the Sun's radiation

and hitherto taken as a causative in¯uence, can, how-

ever, in the lower atmosphere, create only a small

quantity of ions. In the 1890s, then, there was research

into gas-ions and their properties, conducted above all

by J.J. Thomson (1856±1940) and his circle of young

and talented researchers, amongst whom were also

Fig. 7. Arthur Schuster (1851±1934).


C.T.R. Wilson (1869±1959) and Ernest Rutherford

(1871±1937). To create ions they used ultra-violet light,

and Bequerel- and RoÈ ntgen-rays. As already men-

tioned, the electron was discovered in 1897 by J.J.

Thomson. One should note here, however, that even

before Thomson, A. Schuster tried to measure the elec-

tron charge to mass ratio. His measurements, however,

were not su�ciently accurate. Shortly before the end

of the century another development came to the sup-

port of Stewart's and Schuster's ideas Ð wireless tele-

graphy. E.A. Kennely and Oliver Heaviside postulated

around 1900 that a high-altitude ionised layer existed

in the atmosphere, which re¯ected wireless waves. In

our century, and especially since the Second World

War, our knowledge of the outer atmosphere has been

extended further than we could earlier have imagined.

Balfour Stewart's and Arthur Schuster's ideas haveproved extremely fruitful.

8. The ®rst proof of a moving circulating electrical

current in the upper strata of the atmosphere

Another great result of the simultaneous obser-vations conducted on four days in February andMarch 1896 was the precise evidence of a transient cir-

cular electrical current in northern latitudes, recordedby Schmidt (1899). Since the First Polar Year, this Sec-ondary School (Gymnasium) teacher, and from 1902

Eschenhagen's successor at Potsdam, had turned to thestudy of geomagnetism, and done scienti®c work withGeorg Neumayer. On 28 February 1896, during the

time set for simultaneous observation, a magnetic dis-

Fig. 8. Adoef Schmidt (1860±1944).


turbance was noted, observations being made every 5 sfor the duration of the disturbance. Eschenhagen pub-

lished the complete data. In his analysis, Schmidt eval-uated the observational traces and tabulations of 10European stations, and made use of the ``vector dia-

grams'' of geomagnetic variations that von Bezold(1897) had introduced. Schmidt (Fig. 8) was thus ableto show that the ``Konvergenzpunkt der StoÈ rung-

skraÈ fte'' (``convergence point of the disturbing forces'')or the ``Aktionszentrum'' (``centre of action'') movedin the northern hemisphere at a speed of approxi-

mately 1 km/s. There were, then, in the upper atmos-pheric layers ``wandernde Stromwirbel gleich denZyklonen und Antizyklonen des Luftmeeres'' (``wan-dering swirls of electrical currents resembling the

cyclones and anticyclones of the atmosphere''). Thecreation of such electrical circulating currents Schmidtascribed to ``wechselnden Zustand der Sonne zu, der

vielleicht mit Schwankungen der IntensitaÈ t gewisserStrahlenarten verbunden ist'' (``the changing conditionof the Sun which perhaps has to do with intensity of

certain kinds of rays'') (see Schmidt, 1899, p. 386,393).

9. Concluding thoughts

In an age when we have automatic recording instru-ments equipped with photoelectric cells, photoresistors,phototransistors and other semiconductors, when data

are electronically stored, and presented to us at ourcommand by electromagnetic waves, the ®rst self-acti-vating photographic magnetometers may seem primi-tive and perhaps not interesting enough for serious

historical consideration. Let us not forget, however,that they provided geophysicists with their ®rst reliablecontinuous data. The exploration of a close inter-

relation between the Sun and terrestrial magnetismwas thus powerfully advanced. In our own centurythere then developed an intensive investigation of the

ionosphere, and a new geophysical discipline, aero-nomy, has established itself. Space rockets and satel-lites now watch over the Van Allen Belts that

surround our Earth. They give us knowledge of whathappens at the edge of the magnetosphere. Just howthe geomagnetic pulsations arise is still the cause ofsome debate amongst geophysicists. Probably it is a

matter of magnetohydrodynamic waves spreading outfrom the magnetosphere into the ionosphere (Paetzold,1997).

10. References from unpublished sources

1. Description of Mr. T.B. Jordan's mode of photogra-

phically registering the indications of MeteorologicalInstruments. Report of the Royal Cornwall Poly-

technic Society, 1838.2. Fig. 1 taken from: Photographic self-registering

magnetic and meteorological apparatus. Invented by

Charles Brooke. Extracted from the IllustratedMagazine of Art, No. 13, 1854, Fig. 1.

3. The account is to be found in: Polarakten des Bun-

desamtes fuÈ r Seeschi�ahrt und Hydrographie inHamburg. Mikro®che Nr. 478a 2/4, 8 ps.

Acknowledgements

We are grateful to the referees for their very helpful

comments.

References

Arendt, Th., 1896. Beziehungen der elektrischen

Erscheinungen unserer AtmosphaÈ re zum Erdmagnetismus.

Das Wetter, 13. Jg., pp. 241±253, 265±285.

Bartels, J., 1937. Solar eruptions and their ionospheric e�ect

Ð a classical observation and its new interpretation.

Terrestrial Magnetism and Atmospheric Electricity 42,

235±239.

Brooke, Ch., 1846. On the automatic registration of magnet-

ometers and other meteorological instruments by pho-

tography, Phil. Trans. Further constructions and

improvements until 1952.

Eschenhagen, M., 1894. Ergebnisse der Magnetischen

Beobachtungen in Potsdam in den Jahren 1890 und 1891.

VeroÈ �entlichungen des Kgl. Preuss. Meteorologischen

Instituts, Hrsg.: W. von Bezold. Berlin. Pict. p. XXXVIII

(Hauptsystem).

Eschenhagen, M., UÈ ber die Aufzeichnung sehr kleiner

Variationen des Erdmagnetismus. Sitzungsberichte der

Kgl. Preuss. Akademie der Wissenschaften zu Berlin. Jg.

1896, Berlin, 1896, pp. 965±966 mit Tafel; UÈ ber schnelle

periodische VeraÈ nderungen des Erdmagnetismus von sehr

kleiner Amplitude. Sitzungsber. d. Akad. d. Wiss. Berlin,

Jg. 1897, Berlin, 1897, pp. 678±686 with plate.

Eschenhagen, M., 1898. Internationale Magnetische Simultan-

Beobachtungen 1896. Anhang zu Ergebnisse der magne-

tischen Beobachtungen in Potsdam im Jahre 1896.

VeroÈ �entl. d. Kgl. Preuss. Meteorol. Instituts, Hrsg. W. v.

Bezold, Berlin.

Eschenhagen, M.,1882/1883. UÈ ber die Ablenkungskonstante

bei den absoluten Bestimmungen der Horizontal-IntensitaÈ t

des Erdmagnetismus mittelst des Lamont'schen magne-

tischen Theodoliten. Deutsches Polarwerk, Bd. 2, pp. 467±

483.

Gauss, C.F., 1839. Allgemeine Theorie des Erdmagnetismus.

Resultate aus den Beobachtungen des Magnetischen

Vereins im Jahre 1838, Leipzig, pp. 1±57, especially p. 50.

Gordon, J.E.H., 1883. A physical treatise of electricity and

magnetism, 2nd ed., vol. 2. London, p. 199.


Kohlrausch, Fr., 1897. UÈ ber sehr rasche Schwankungen des

Erdmagnetismus. Annalen der Physik und Chemie, hrsg.

v. G. und E. Wiedemann, N. F. Bd. 60, pp. 336±339.

Mascart, E., 1900. TraiteÂ de MagneÂ tisme Terrestre, Paris, p.

202; pict. p. 203.

Neumayer, G., BoÈ rgen, C. (Hrsg.), 1886. Die internationale

Polarforschung 1882±1883. 2 Bde. Berlin (im folgenden

abgekuÈ rzt: Deutsches Polarwerk 1882±1883). See: Vorwort

Bd. I, esp. p. (5) and (12), and Bd. 2, Beobachtungen aus

dem Magnetischen Observatorium der Kaiserlichen

Marine in Wilhelmshaven, pp. 359±464.

Paetzold, K.-H., 1997. Hundert Jahre IonosphaÈ renforschung.

In: SchroÈ der, W. (Ed.), Geomagnetism and Aeronomy,

Science Edition. Bremen 32, pp. 125±134.

Ronalds, F., 1847. On photographic self-registering meteoro-

logical and magnetical instruments. Phil. Trans 137, 111±

117.

Sabine, E., On periodical laws discoverable in the mean e�ects

of the larger magnetic disturbances. Phil. Trans., 1851,

123±139 und 1852, 103±124.

Schmidt, A., 1899. UÈ ber die Ursache der magnetischen

StuÈ rme. Meteorol. Zeitschr., hrsg. von J Hann und G.

Hellmann, Wien. 16, 385±397.

Schmidt, A., Erdmagnetismus (abgeschlossen 1917).

EncyklopaÈ die der mathematischen Wissenschaften mit

Einschluû ihrer Anwendungen. 6. Bd., 1. Teil Geophysik.

Hrsg. von Ph. FurtwaÈ ngler und E. Wiechert. Leipzig

1906±1925, pp. 267±396, here to pp. 381±389.

SchroÈ der, W., 1974. Hermann Fritz und sein Wirken fuÈ r die

Polarlichtforschung. In: Birett, H., et al. (Eds.), Zur

Geschichte der Geophysik. Springer Verlag, Berlin,

Heidelberg, New York, pp. 149±151.

SchroÈ der, W., 1999. The Aurora in Time, Science Edition.

Bremen, 1999.

SchroÈ der, W., 1984. Das PhaÈ nomen des Polarlichts.

Wissenschaftliche Buchgesellschaft, Darmstadt, 1984, 156

pp.

SchroÈ der, W., Wiederkehr, K.H., 1992a. G.v. Neumayer und

die internationale Entwicklung der Geophysik. 1. Teil:

Meteorologie. Gesnerus 49, 45±62.

SchroÈ der, W., Wiederkehr, K.H., 1992b. G.v. Neumayer

(1826±1909) und die internationale Entwicklung der

Geophysik. 2. Teil: Erdmagnetismus. Gesnerus 49, 376.

SchroÈ der, W., Wiederkehr, K.H., 1997. UÈ ber BeitraÈ ge geophy-

sikalischer Forschungen zum Umbruch der klassischen zur

modernen Physik vor 100 Jahren. In: SchroÈ der, W. (Ed.),

Geomagnetism and Aeronomy with special historical case

studies. Coll., IAGA History News Letter 29, 66±79.

Schuster, A., 1886. On the diurnal period of terrestrial mag-

netism. Philosophical Magazine 21 (5 Ser.), 349±359.

Schuster, A., 1889. The diurnal variation of terrestrial mag-

netism. Phil. Trans. Roy. Soc. London 180A, 467±518. In

addition on Schuster's pioneering work in geomagnetism

see S. Chapman and J. Bartels in: Terr. Magn. and Atm.

Electr., vol. 39, 1934, p. 341. Picture of Schuster p. 264.

Scott, R.H., 1885. The history of the Kew-Observatory.

Proceedings of the Roy. Soc. of London 39, 37±76.

Stewart, B., 1878. On the variations of the daily range etc.

Proceed. of the Roy. Soc. of London, 102±121.

Stewart, B., 1883. Article ``Meteorology, Terrestrial

Magnetism''. Encyclopaedia Britannica. 9th ed., vol. 16,

Edinburgh, 1883, pp. 181±184.

Stewart, B., 1961. On the great magnetic disturbance which

extended from August 28 to September 7, 1859, as

recorded by photography at the Kew Observatory.

Philosophical Transactions of the Royal Society of

London 1861, 423±430.

SuÈ ring, R., 1911. Meteorologie. Photographische

Registriermethoden. In: Wolf-Czapek, K.W., Angewandte

Photographie in Wissenschaft und Technik. 4 Teile. Berlin,

1911, I, pp. 62±68.

van Bemmelen, W., 1899. Spasms in the Terrestrial Magnetic

Force at Batavia. Kon. Akad. v. Wetensch. te Amsterdam,

pp. 202±211; Pulsations de la force magnetique terrestre.

Arch. NeÂ erland d. Sciences exact. et nat., Ser. II, vol. 6,

1901.

von Bezold, W., 1897. Zur Theorie des Erdmagnetismus.

Sitzungsberichte d. Kgl. Preuss. Akad. d. Wiss. zu Berlin,

Jg. 1897, 1. Halbbd., Berlin, 1897, pp. 414±449.

von Bezold, W., 1902. Nachruf auf Max Eschenhagen.

Verhandl. Dt. Phys. Ges 4, 79±87.

von Lamont, J., 1851. Astronomie und Erdmagnetismus.

Stuttgart, 1851, p. 272.

Wiederkehr, K.-H., 1997. Die Erforschung der Nebelbildung

Ð Beispiel einer Ver¯echtung von Meteorologie und

Physik. In: W. SchroÈ der (Ed.), Geomagnetism and

Aeronomy, Science Edition. Bremen, 1997, pp. 225±234.


a history of the early recording of geomagnetic variations

Documents