Measuring Magnetism: Retrospective on Theories and Instruments from Lucretius to Blackett and Bullard
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Mary Jo Nye
Abstract
Pliny described ancient theories of the attractive power of some kinds of iron rocks for metals, but the first instrument for measuring magnetism was the compass device invented in ancient China. The compass needle appeared to be attracted toward celestial true North, providing a means of locating directions. By the fifteenth century, there was recognition that the needle deviates slightly from the Pole Star (declination), suggesting that the attracting power lies elsewhere, perhaps in magnetic rocks in the north or, as assumed by William Gilbert around 1600, in iron material within the Earth, since the needle dips from the horizon (inclination). The current dynamo theory that the Earth’s magnetic field originates in the Earth’s electrically charged molten core emerged in the mid-twentieth century from competing approaches taken by the physicists Patrick Blackett and Edward Bullard after Blackett disproved his own much updated version of Gilbert’s idea.
Abstract
Pliny described ancient theories of the attractive power of some kinds of iron rocks for metals, but the first instrument for measuring magnetism was the compass device invented in ancient China. The compass needle appeared to be attracted toward celestial true North, providing a means of locating directions. By the fifteenth century, there was recognition that the needle deviates slightly from the Pole Star (declination), suggesting that the attracting power lies elsewhere, perhaps in magnetic rocks in the north or, as assumed by William Gilbert around 1600, in iron material within the Earth, since the needle dips from the horizon (inclination). The current dynamo theory that the Earth’s magnetic field originates in the Earth’s electrically charged molten core emerged in the mid-twentieth century from competing approaches taken by the physicists Patrick Blackett and Edward Bullard after Blackett disproved his own much updated version of Gilbert’s idea.
Kapitel in diesem Buch
- Frontmatter 1
- Acknowledgements
- Contents VII
- List of Figures and Tables IX
- Prologue: of Friendship and Fishponds 1
- Introduction 5
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Part I: Historiography, Disciplinary Categories, and Anachronism
- Greco-Roman Histories of Astronomy, Their Genres, and Their Afterlives 15
- When was Cosmology? The Curious History of a Disciplinary Category 33
- Surmise or Certainty: Women in Science in Antiquity 51
- Deep Reading of Kepler’s New Astronomy: An Exercise in Computational History of Science 65
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Part II: Scientific Writing: Genres, Authority, Authorship, and Audiences
- Narrative Elements in Aristotle’s Generation of Animals 83
- Style and Intended Readership of Theophrastus’ On Fire (De igne) 95
- Strategies of Moralising in the Pseudo-Vergilian Aetna 115
- Leonides of Alexandria’s Isopsephic Epigrams: An Astronomical Art? 131
- Faithful Marriages and Wild Unions: Palladius’ On Grafting 153
- Ancient Authority in Arabic-Islamic Scientific Writing and Practice 169
- “A Cabinet of Many Rare Secrets”: The Uses and Abuses of Aristotle’s Masterpiece 191
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Part III: Counting and Measuring: Tools, Diagrams, and Replicas
- The Various Uses of Numbers and Mathematics in Ancient Egypt 219
- Greek Sexagesimals and Zeros 231
- The Diagrams and Replicas of Richard of Wallingford’s Clock 253
- Measuring Magnetism: Retrospective on Theories and Instruments from Lucretius to Blackett and Bullard 279
- Ancients and Moderns in Tycho Brahe’s Astronomy 295
- List of Contributors 317
- Bibliography
- Index
- Index Locorum
Kapitel in diesem Buch
- Frontmatter 1
- Acknowledgements
- Contents VII
- List of Figures and Tables IX
- Prologue: of Friendship and Fishponds 1
- Introduction 5
-
Part I: Historiography, Disciplinary Categories, and Anachronism
- Greco-Roman Histories of Astronomy, Their Genres, and Their Afterlives 15
- When was Cosmology? The Curious History of a Disciplinary Category 33
- Surmise or Certainty: Women in Science in Antiquity 51
- Deep Reading of Kepler’s New Astronomy: An Exercise in Computational History of Science 65
-
Part II: Scientific Writing: Genres, Authority, Authorship, and Audiences
- Narrative Elements in Aristotle’s Generation of Animals 83
- Style and Intended Readership of Theophrastus’ On Fire (De igne) 95
- Strategies of Moralising in the Pseudo-Vergilian Aetna 115
- Leonides of Alexandria’s Isopsephic Epigrams: An Astronomical Art? 131
- Faithful Marriages and Wild Unions: Palladius’ On Grafting 153
- Ancient Authority in Arabic-Islamic Scientific Writing and Practice 169
- “A Cabinet of Many Rare Secrets”: The Uses and Abuses of Aristotle’s Masterpiece 191
-
Part III: Counting and Measuring: Tools, Diagrams, and Replicas
- The Various Uses of Numbers and Mathematics in Ancient Egypt 219
- Greek Sexagesimals and Zeros 231
- The Diagrams and Replicas of Richard of Wallingford’s Clock 253
- Measuring Magnetism: Retrospective on Theories and Instruments from Lucretius to Blackett and Bullard 279
- Ancients and Moderns in Tycho Brahe’s Astronomy 295
- List of Contributors 317
- Bibliography
- Index
- Index Locorum
