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D'Entrecasteaux, 1792: Celebrating a bicentennial in geomagnetism



The first surveys of global magnetic intensity, and especially the demonstration of its variation with latitude, are commonly credited (for example, Chapman, [1967]) to Alexander Von Humboldt, who played a major role in developing geomagnetism in the late 18th and 19th centuries. Von Humboldt made intensity measurements in South America from 1798-1803 and later encouraged the establishment of a global magnetic observatory network (see, for example, Malin and Barraclough, [1991]).However, as pointed out by Sabine [1838] in a review of intensity measurements to that time, the earliest surviving survey of global magnetic intensity, showing it to strengthen away from the equator both north and south, was made by Elisabeth Paul Edouard De Rossel during the 1791-1794 expedition of Bruny D'Entrecasteaux. Even earlier measurements seem certain to have been made by the scientist Robert de Paul, chevalier de Lamanon (always referred to as Lamanon) of the La Pérouse expedition [Milet-Mureau, 1799], but any records are evidently lost. Lamanon died when the La Pérouse expedition was in Samoa in 1797, and both ships of that expedition were wrecked on the island of Vanikoro, presumably in 1788 [Marchant, 1967; Spate, 1988]. All such measurements were of relative magnetic intensity until a method for the determination of absolute intensity was invented by Gauss in 1832. For a recent discussion of this latter topic, see Jackson [1992].
... [45] An expedition of two ships under Bruny d'Entrecasteaux was sent in 1791 to search for the La Pérouse expedition [Lilley and Day, 1993]. Elisabeth Paul Edouard de Rossel (1765 -1829) reported six magnetic intensity measurements performed by timing 100 oscillations of a vertical dip needle (Figure 8) [de Rossel, 1808]. ...
... 97 and 102], see also Sabine [1838]). Lilley and Day [1993] have replotted de Rossel's data (dip as a function of oscillation period), fitting them very nicely with the formula for a tilted geocentric dipole and deriving the calibration constant for the instrument. ...
... Inclinometer of E. P. E. de Rossel (used 1791 -1794) [fromLilley and Day, 1993]. ...
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This paper summarizes the histories of geomagnetism and paleomagnetism (1269–1950). The role of Peregrinus is emphasized. In the sixteenth century a debate on local versus global departures of the field from that of an axial dipole pitted Gilbert against Le Nautonier. Regular measurements were undertaken in the seventeenth century. At the turn of the nineteenth century, de Lamanon, de Rossel, and von Humboldt discovered the decrease of intensity as one approaches the equator. Around 1850, three figures of rock magnetism were Fournet (remanent and induced magnetizations), Delesse (remagnetization in a direction opposite to the original), and Melloni (direction of lava magnetization acquired at time of cooling). Around 1900, Brunhes discovered magnetic reversals. In the 1920s, Chevallier produced the first magnetostratigraphy and hypothesized that poles had undergone enormous displacements. Matuyama showed that the Earth's field had reversed before the Pleistocene. Our review ends in the 1940s, when exponential development of geomagnetism and paleomagnetism starts.
... Over the following 2 years, the d'Entrecasteaux expedition with physicist Elisabeth Paul Edouard de Rossi (male) undertook pioneering research of worldwide importance, showing that the geomagnetic field increased in strength with increasing latitude. Details of this work were reported by de Rossel (De Rossel 1808; Lilley and Day 1993). Without a method to directly measure the strength of the geomagnetic field the instrument of the time was a dip meter (Fig. 1a). ...
... De Rossel's dip meter instrumentation 1792. b Period of oscillation variation with magnetic dip angle at various locations in latitude (after De Rossel 1808; fromLilley and Day 1993) ...
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Solar-terrestrial physics research in Australia began in 1792 when de Rossel measured the southern hemisphere geomagnetic field at Recherche Bay on the southern tip of Tasmania, proving the field magnitude and direction varied with latitude. This was the time when the French and British were competing to chart and explore the new world. From the early twentieth century Australian solar-terrestrial physics research concentrated on radio wave propagation and communication, which by the 1950s fed into the International Geophysical Year in the areas of atmosphere and ionosphere physics, and geomagnetism, with some concentration on Antarctic research. This was also the era of increased studies of solar activity and the discovery of the magnetosphere and the beginning of the space age. In the 1960s, Australia became a world leader in solar physics which led to radio astronomy discoveries. This paper outlines the historical development of solar-terrestrial physics in Australia and its international connections over the years and concludes with examples of specific research areas where Australia has excelled.
... Even though inclination was recognized around 1600 by "Robert Norman (Norman, 1720)", few inclination data were recorded in the ships' logs and most of these data were in the late 18th century and few before that as shown in Fig. 2. The reason for this was partly the difficulty of measuring inclination whilst on a ship, also, inclination was not used in navigation as declination was at that time [12]. Von Humboldt made relative intensity measurements in South America in 1798 and intensity data start to appear in the southwest Pacific about the same time as shown in Fig. 2. The method of measurement was by timing the oscillations of the ship's dip needle [16]. Elisabeth Paul Edourd De Rossel made the first magnetic intensity measurements recorded in the southwest Pacific during 1791-1794 [17]. ...
A spherical cap harmonic analysis (SCHA) model has been used to derive a high resolution regional model of the geomagnetic field in the southwest Pacific region over the past 400 years. Two different methods, a self-consistent and the gufm1 dipole method, have been used to fill in gaps in the available data. The data used in the analysis were largely measurements of the magnetic field recorded in ships logs on voyages of exploration in the region. The method chosen for the investigation used a spherical cap of radius
... , where I and m are the moment of inertia and the magnetic moment of the needle, respectively, and B is the magnetic field. The first recorded intensity measurements were made by de Rossel on the d'Entrecasteaux expedition of 1791-94 (Lilley and Day, 1993). Both the d'Entrecasteaux measurements and those of Alexander von Humboldt, made between 1798 and 1803, clearly show the increase of intensity with latitude, which is expected of a predominantly geocentric axial dipole (GAD) field. ...
In this chapter the instruments and techniques employed in a wide range of geomagnetic measurements are described. These range from the real-time records made and archived by geomagnetic observatories around the globe to paleomagnetic measurements of the natural remanent magnetization of rocks and their interpretation in terms of the prehistoric field. They include ground-based, shipborne, and airborne magnetic surveys made to chart anomalous fields or for exploratory purposes. Both historical instruments, some of which were used in key pioneering studies, and modern, state-of-the-art equipment are described. Also outlined are some of the procedures used in the reduction and interpretation of geomagnetic, magnetic survey and palaeomagnetic data.
... Briefly, the oldest surviving records indicating geographic differences in field intensity are those due the French captain, Elisabeth P.E. De Rossel, who measured relative intensity by observing the oscillation rate of a magnetized needle during the 1791-1794 expedition of the Bruny D'Entrecasteaux (e.g., Lilley and Day, 1993). De Rossel noted, in particular, that magnetic intensity was greatest near the magnetic poles and least near the magnetic equator. ...
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The Earth’s atmosphere occupies some million times greater volume than the solid Earth. In this huge system, the charged plasma particles react strongly to electric and magnetic fields. Hence, electrical processes in one part of the system can influence the electrodynamical processes in another distant part. The redistribution of the charged particles in turn can modify the existing electric and magnetic fields in the atmosphere. Hence, an investigation of electrodynamical processes in various regions of the atmosphere and their coupling is very important for understanding the state of electrical environment of the Earth’s atmosphere.
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