GEOMAGNETISM
(RESEARCH: PAST AND PRESENT)
Wilfried
Schroeder, editor, 2000. Sience Edition /IDCH-IAGA, Darmstadt Germany. 248 p.
Softcover, $30.00.
Review by Ed Mankinen
This book contains a selection of papers from a
symposium on the History of Geophysics at the IAGA (International Association of
Geomagnetism and Aeronomy) Assembly held in Birmingham, UK, August 1999.
Included are introductory remarks by H. Moritz, followed by thirteen papers
authored by twenty prominent researchers in the field of geomagnetism. Because I
cannot do justice to all in the space allotted, I will focus on a few items,
attempting to give a flavor of the overall publication. Although most of my
career has been involved with research in paleomagnetism, this volume is of
interest to me because the history of geomagnetism is, of course, a significant
part of the history of my chosen discipline.
Early studies in geomagnetism, for obvious reasons,
focused on its application to navigation. Although the basic magnetic properties
of lodestone were known in ancient China and Greece, magnetic compasses were
used for navigation for hundreds of years before there was any understanding of
magnetism as something other than a mysterious force of nature. The compass
needle was once thought to indicate the direction toward the north, or pole,
star. Others considered the deviation of the needle to be due to the attraction
of landmasses or to buried deposits of lodestone. Early seafarers were even
subject to severe punishment if found with garlic or onion on their breath
because of a fear that the odor could demagnetize a ship's compass!
In the lead article, “Geomagnetism and Fundamental
Science”, G. P Gregori takes us on a whirlwind historical tour from the time
of the first magnetic charts of the early 1500s to Gilbert's publication of De
Magnete (1600), where he showed that the magnetic field is essentially that
which would be produced if the Earth were itself a uniformly magnetized sphere.
This revelation made it obvious that the deviation of a compass needle could not
be caused by the pole star. The first published isogonic chart as constructed by
Halley is then discussed, as is the discovery of secular variation (Gunter in
1624) and westward drift (Gellibrand in 1635) of the magnetic field - all
leading up to the publication in 1686 of Newton's Principia Mathematica.
With this new theory, it became evident that gravity, not magnetism, was the
force that controlled celestial motions. The chronicle continues with Ampére's
(1820) proof that magnetic and electrical fields are related, Gauss assuming the
responsibility of developing the magnetic observatories in 1834, and on to
modern studies of the origin of the geodynamo.
The articles by M. Mandea, “French Magnetic
Observation and Theory at the Time of De Magnete”, and P. Ultré-Guéard and
M. Mandea, “Declination and Longitude in France in the Early 17th
Century”, discuss observational measurements of the field and the problem of
determining longitude. Among the important items noted here are Nautonier's
realization (~1602-1604)
that the dipole field is tilted with respect to the Earth's rotational axis, and
the completion of the Paris Observatory in 1670. With the latter, the first
systematic program for measuring the geomagnetic field was initiated and has
continued to the present. D. R. Barraclough follows with an excellent summary of
the subject in “Four Hundred Years of Geomagnetic Field Charting and Modelling”.
He includes some fundamental discoveries in geomagnetism and provides a succinct
description of geomagnetic field models - including the-first “modern”
mathematical model, which was produced by Gauss in 1839.
Since the early emphasis on its navigational aspects,
geomagnetism has turned more toward fundamental research into the Earth's
interior and the near-space environment. The articles “Edmond Halley and the
Earth's Magnetic Field” by A. Cook and “Edmond Halley's Voyages in the
Paramore and the First Isogonic Chart of the Earth's Magnetic Field” by T. D.
G. Clark were particularly interesting to me, because Halley apparently was
among the first to bridge the gap between the two aspects of geomagnetism. He
recognized a need for and set up expeditions to collect observational data, and
he also published the first charts of equal magnetic declination for the entire
Atlantic Ocean. He later foresaw that the magnetic field must have its origin in
the Earth's interior and recognized the problem of geomagnetic secular
Variation. He also realized that there was a connection between the Earth's
field and the aurora. Although many know Halley for his work in astronomy (i.e.,
Halley's comet), Cook also reminds us that Halley, as Clerk of the Royal
Society, prompted Newton to begin writing his Principia Mathematica and
saw to its eventual publication.
Those interested in near-space environment will find
several articles of interest. 0. Beckman, in “A Magnetic Storm-Simultaneously
Registered at Two Sites in 1741”, recounts the observation by Celsius and
Hiorter of the connection between a sudden displacement of a magnetic needle and
the appearance of an aurora. H. Yoshida describes Tanakadate's research on
electrical currents between the Earth's surface and the.atmosphere in “A.
Tanakadate and His Study on Vertical Currents”. A. Àdàm', P. Benze, and J.
Veroe describe the establishment of the Nagycenk Observatory (“The Nagycenk
Observatory and Its Long Data Series”) in 1957 and its recording of the
Earth's electromagnetic field. H. and K.-H. Bernhardt briefly describe the
career of Julius Bartels in “Remarks on Life and Scientific Work of Julius
Bartels (1899-1964)”. Finally, M. Colacino, 0. Ferrante, and M. R. Valensise
comment on. the ill-fated scientific expedition of the airship Italia in
“The Unpublished Correspondence Between Nobile and Eredia for the Preparation
of the 1928 Polar Expedition”.
It is important to remember that much of the highly
significant early research in geomagnetism was occurring at a time when
scientific inquiry was not always well received. G. Scalera uses case studies in
“Religious Dogma and Earth Sciences at the Turning Point of the Renaissance”
to examine the reaction to certain scientific ideas and. why they, might have
differed. Finally, G. P and L. G. Gregori provide a perspective on
“Archaeoastronomy (An Updating) and Anthropological Aspects of Architecture”.
The authors introduce the term “anthropological architecture” to convey the
idea that early civilizations used the design, plan, and orientation of
buildings and monuments for the management of time and space (for example,
seasonal measurement and geographical orientation, among others).
In any collection of papers such as this, the focus of
each is on certain aspects of the history of geomagnetism from the viewpoint of
the different authors. Many, however, refer to some degree to earlier and/or
related studies, so a coherent picture eventually emerges. Extensive reference
lists can be found in the papers presented, and readers wanting to pursue
subjects in greater depth can easily do so. Scattered throughout the volume are
a few sketches, maps, and notes (thankfully translated) from some of the early
researchers that I found quite interesting. Because the book is in paperback and
is a reproduction of articles submitted by many authors, it is not uniform in
typeface or style of presentation. However, this does not detract greatly from
the content; this method of publishing should put the price of the volume well
within reach of a broad audience, who should enjoy reading it, as have I.