| Summary: | Geomagnetism (also known as terrestrial magnetism) is the scientific study of the earth from the point of view of its magnetic properties. The alignment of a natural or artificial magnet in a north-south direction is only the best known of these. The discovery of other properties, such as the separation of the magnetic poles from the geographic poles of the earth and the "dip" of the needle in arctic (and antarctic) latitudes, interested the scientifically inclined as early as Columbus. Mariners, who had reason to be most interested in the compass, were prominent in the study into the 18th century. But as more and more magnetic peculiarities were discovered the apparent movement of the poles, the changes in direction, dip, and magnetic strength from year to year and even from day to day, and magnetic irregularities apparently connected with other atmospheric phenomena the aurora borealis the subject was taken over by the scientists. While Alexander von Humboldt, famous as a scientific traveler in the early 19th century, promoted world-wide measurement of geomagnetic phenomena, less adventurous scientists occupied themselves with the development of more sensitive instruments and more sophisticated methods. Geomagnetism attracted the attention of such leading scientists of the 19th century as John Herschel and C. F. Gauss. One consequence was that this speciality became prominent in the establishment of international cooperation in science. In nations, such as the United States and Russia, that were both geographically large and underdeveloped, the study of geomagnetism assumed unusual importance as a kind of training ground for scientists. As time passed, however, it became clear that the numerous scientific questions posed by the subject were not to be easily answered. Geomagnetism consequently tended in the later 19th century to be absorbed by meteorology, another science whose practitioners were accustomed to continuous and tedious measurement with little scientific consequence. Geomagnetic measurements also joined gravity measurements as conventional duties of the geodetic surveyor. Most interesting, in the later 19th century, was the development of instruments capable of making different measurements simultaneously under difficult conditions, and often automatically. In the first half of the 20th century geomagnetism became one of the topics handsomely supported by the new Carnegie Institution of Washington (which was seeking "neglected" sectors of science that were also of international interest). Then, as it was found that magnetic "anomalies" were exhibited by petroleum bearing land, the subject attracted unprecedented material support. After a generation it began at last to seem significant to science at large, in its role in the spectacular development of "plate tectonics." Our collection and this history end at this point. SISP
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