A Millennium of Geomagnetism

Abstract

The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert's De Magnete [Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André‐Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.

Profile of Jean-Pierre Sauvage, Sir J. Fraser Stoddart, and Bernard L. Feringa, 2016 Nobel Laureates in Chemistry

“…This latter discovery laid the foundation for Stoddart's seminal report (15) in 1989 of the first template-directed synthesis that used through-space donor-acceptor interactions (Fig. 2B) to synthesize an all-organic [2]catenane in 70% overall yield. Analogous to Sauvage's "threading" approach, Stoddart's group also used ( Fig.…”

“…The beginning of the 19th century revealed as much when Alessandro Volta reported (1) the first electrical battery-now referred to as a Voltaic cell-using stacks of copper and zinc plates separated by a sulfuric acid electrolyte. This discovery of a constant electrical energy source later led to Hans Christian Oersted's observation of electromagnetic fields in 1820 (2), Michael Faraday's vertical conducting wire orbiting around a magnet in 1821 (3), and eventually Joseph Henry's report (4), in 1831, of a small rocker actuated by reciprocating magnetic attraction and repulsion, the latter of which is considered by many to be the first electric motor. At that time, it was not clear what application Henry's invention might fulfill, and even he admits in his manuscript to the editor that, ".…”

“…Sauvage's group demonstrated (11) later that the copper(I) atom could be removed either chemically with KCN, or through electrochemical oxidation of copper(I) to copper(II). The loss of the copper atom from the center of the [2] catenate affords a [2]catenane 5, where each phenanthroline subunit rotated away from one another. Although this first example of using a template-directed protocol produced what many would consider to be a molecular "switch" rather than a "machine," the importance of Sauvage's seminal work cannot be overstated.…”

“…Before Sauvage's doctoral studies, the synthesis of interlocked structures-specifically [2] catenanes, which consist of two noncovalently interlocking molecular rings-had been achieved either through a low-yielding statistical protocol (8), or by using a directed covalent approach (9) that was quite laborious, because it required many synthetic steps and afforded only modest overall product yields. In 1983, while a professor at the University of Strasbourg, Sauvage demonstrated ( Fig.…”

“…2A) the first high-yielding template-directed synthesis of a [2]catenane by capitalizing on a "threading" approach where the formation of a tetracoordinate complex 2⊂1 + is achieved between a "closed" phenanthroline-based macrocycle 1 and an "open" phenanthroline diol 2 centered about a copper(I) metal atom (10). The stability of this complex is sufficiently high to allow for the ring-closing step, which proceeds through two nucleophilic substitutions of a diiodo oligoethylene glycol 3, resulting in a 42% yield for the desired [2]catenate 4 + . Sauvage's group demonstrated (11) later that the copper(I) atom could be removed either chemically with KCN, or through electrochemical oxidation of copper(I) to copper(II).…”