Place · fort & measurement site · Pakistan
Nandana, the Salt Range
Also known as Nandana, Nandna, Salt Range, Baba Wali Kandhari
A hill fort in the Salt Range above the Jhelum where al-Bīrūnī, about 1018, measured the angle of dip to the horizon from a hilltop of known height and used it to compute the radius of the earth — arriving at a figure within about half a percent of the modern value.
- Function
- Military & resistance
- Confidence
- Established / referenced
- Location
- 32.723, 73.276
Worth knowing
The method needs one measurement and one trigonometric identity, and he says he took it because he could not get to the plains of Iraq where his predecessors had used the longer baseline method. A Ghaznavid frontier fort is therefore the site of the most accurate pre-modern measurement of the size of the earth.
Connections (2)
- Imperial administration ofGhazni
Ghazni is where he was kept and Nandana is where he did the one piece of fieldwork the Tarikh al-Hind's reputation rests on. A Ghaznavid frontier fort in the Salt Range is therefore the site of the most accurate pre-modern measurement of the size of the earth, made by a man travelling with an invading army because he had no choice about where he was.
- Site adjacencyKhewra Salt Mine
Both sit on the Salt Range escarpment within about forty kilometres of each other, and both are about the same geology. Nandana was the Hindu Shahi fort where Mahmūd of Ghazni fought in 1014, and where al-Bīrūnī later measured the earth's radius using the dip of the horizon from its height. Khewra is the salt itself — a Precambrian evaporite seam worked into nineteen storeys of tunnel. The range that gave the Shahis their frontier forts also gave colonial India one of its principal revenue monopolies.
On these journeys
- The Hindu Shahi frontier
- Al-Bīrūnī — the scholar in Maḥmūd's train (c. 1017–1030)
- The north-west — Gandhara, the Indus and the Hindu Kush
Sources
Wikipedia, “Nandana Fort”. Al-Bīrūnī, Kitāb Taḥdīd nihāyāt al-amākin, on the dip measurement; S.H. Nasr on al-Bīrūnī's geodesy.
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