c. 1701 AD
Halley maps magnetic variation
Oceans, navigation & cartography · Nautical cartography · Instruments & positioning
Edmond Halley assembled ocean observations and drew lines joining places with equal compass variation. The chart turned a changing magnetic phenomenon into navigable information and was an early use of isolines, although it depended on incomplete measurements and required updating.
Precision, calendar, and review
- Start
- year · approximate
- Calendar and convention
- Historical-era years; the source calendar is not identified. No conversion of days is assumed.
- Year zero
- The scale goes from 1 BCE to 1 CE without year zero. Changing era names changes labels only.
- Documentary review
- Date not recorded
Reading the date: point event.
Sources
- www.rmg.co.uk (opens in a new tab)
Source provenance and scope
- Publication date
- Not identified in metadata; document review pending
- Bibliographic date checked
- 2026-09-23
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