Magnetism, Navigation, and Cartography in the Early Modern Period: An Elusive Relationship
Bibliographic record
Abstract
Following the introduction of the marine compass in Europe during the last decades of the thirteenth century, an intimate – and sometimes problematic – relationship between the Earth’s magnetism, navigation and nautical cartography developed. Because charts were constructed using uncorrected compass courses collected by pilots at sea, their coastlines often appeared distorted, reflecting the effect of magnetic declination. Although the phenomenon was acknowledged by the late fifteenth century, serious consideration of its effect on charts was slower to come. This status quo was first put in question after Magalhães and Elcano’s voyage to South-East Asia (1519–1522), when it was realized with surprise that, contrary to contemporary nautical cartography, the coveted Spice Islands were not situated in the Spanish hemisphere, according to the terms the Treaty of Tordesillas. The issue triggered a long discussion between politicians, cosmographers, chart-makers, and pilots, not only about the necessity of correcting the mistake but also about how navigation should be conducted and charts made. At the core of the debate was the inescapable clash between the contemporary cartographic model, based on routes, and the Ptolemaic map prescriptions, based on geographical coordinates. This article explores how nautical cartography responded to such issues. By analysing the geometry of Africa in early modern charts of different origins, the author first clarifies whether and when they began to be corrected for magnetic declination and then offers hypotheses about how and why those changes were made. The results indicate that rather than correcting the orientation of coastlines on charts to conform with either true geographical directions or up-to-date compass readings, the adjustments involved astronomical measurements of longitude.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.003 | 0.020 |
| Scholarly communication | 0.004 | 0.003 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".