Robinson McLaughry Yost

Major Professor: David B. Wilson

Iowa State University

This dissertation investigates a neglected area in the history of the physical sciences— the history of the study of magnetism. Examining the study of magnetism and terrestrial magnetism in Great Britain from the 1750s to the 1830s allows for discussing the changing motives, methods, and results of magnetic and geomagnetic studies. The changes in magnetic studies are comparable to dramatic transformations in other areas of experimental physics, including the studies of heat, light, and electricity.

With the publication of De Magnete, William Gilbert intimately linked the earth's magnetism to magnetism by arguing the earth was a giant magnet. Though subsequent Cartesian theories assumed the circulation of a material magnetic fluid, they retained the Gilbertian notion that the earth and ordinary magnets had the same causes. Because the analogy persisted into the nineteenth century, theories of magnetism and terrestrial magnetism were frequently discussed together.

The impetus for collecting geomagnetic data changed between 1750 and 1835. Around 1800, the discovery of ship magnetism lent important practical reasons for understanding magnetism. As well, magnetic collecting took on new importance with renewed Arctic exploration in 1818. Tracing the changing motives behind and methods of collecting magnetic data reveals its shifting practical, scientific, and symbolic importance.

Mystery and confusion surrounded the study of magnetism from 1750 to 1790. While important, the study of magnetism was much less studied than electricity. Though most endorsed circulating fluid theories, there was little consensus regarding the causes of terrestrial magnetism. In the meantime, many speculated that unifying principles, such as Newton's ether, linked all phenomena together.

From 1780 to 1820, mathematical and quantitative imponderable fluid theories of Aepinus and Coulomb displaced the qualitative circulating fluid theories. In Britain, John Robison and several others made known Aepinian theory. Scottish methodology and Laplacian science played vital roles in changing the face of British experimental physics. Between 1820 and 1840, magnetic theories changed with the discovery of electromagnetism and subsequent flood of experimentation. Challenges to Laplacian orthodoxy supposed that magnetism, electricity, heat, light, chemical action, and rotation were intimately connected. Meanwhile, the Humboldtian-cosmical approach altered the understanding of geomagnetism as well.

Many assisted in completing this dissertation. I would like to thank them for their help and support. My stay at the Linda Hall Library in Kansas City, Missouri, as 1996 Summer Research Fellow contributed significantly to my research. I particularly thank Bruce Bradley for his patient and friendly assistance. I also thank Leslie Overstreet of the Smithsonian Institution Libraries (Special Collections) for her assistance during my brief visit. Thank you as well to Dr. Gregory A. Good whose encouragement at the 1995 History of Science meeting, e-mail correspondence, and generous loaning of a dissertation helped me enormously. Also a thanks to Iowa State's Interlibrary Loan (particularly Frank Dunnick) whose efficiency placed many difficult-to-reach sources within my grasp.

I also thank my major professor, David B. Wilson, for reading drafts of the various chapters. His insightful comments kept me on the right track. Thanks as well to the professors who have given me direct and indirect encouragement; these include Robert Schofield, Alan I Marcus, Alan Wilt, Don Rawson, Ken Madison, Andrejs Plakans, and Philip Zaring. Also a big thank you to Carole Kennedy for her help and support.

Last but not least, thanks go to family and friends. In particular, I thank my parents for their love and support. Also, I thank Jeff Weber, Anne Slakey, Phil Frana, Theresa Rudd, Herb Folsom, Alison Kovac, Stephanie Carpenter, and Bruce Homann. I cannot forget my long-time Ames roommates, Trudi, Peter, and Dylan Matthews; without their friendship I never would have finished. A personal thank you to Laura Lacasa, my best friend, for her support and love. Finally, I thank God for getting me through these six stressful, yet challenging years.

CHAPTER 1: INTRODUCTION (c.1600-1750)

CHAPTER 2: GLOBAL MAGNETIC COLLECTING (c.1750-1835)

CHAPTER 3: MAGNETISM: MYSTERIOUS, IMPORTANT, CONFUSING (c.1750-1790)

CHAPTER 4: PONDERING THE IMPONDERABLE (c.1775-1815)

CHAPTER 5: FRENCH PHYSICS IN GREAT BRITAIN (c.1800-1820)

CHAPTER 6: CONCLUSION: NATURE'S FORCES UNITED? (c.1800-1835)

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