Al-Biruni reasoned his way to an unknown continent across the ocean
In 1037, centuries before Columbus sailed, the Persian scholar al-Biruni argued that land must lie in the great ocean between Asia and Europe. His logic was geometric: Afro-Eurasia covered only two-fifths of the globe's circumference, and whatever forces raised those continents surely raised others. He even guessed that some of it would be inhabited.
Abu Reyhan al-Biruni was born around 973 in an outlying district of Kath, capital of Khwarazm, in what is now Karakalpakstan in Uzbekistan; his name comes from a Persian word for outskirts. He grew up speaking Khwarezmian, an Eastern Iranian language, and later worked in Persian, Arabic and Sanskrit, with some Greek, Hebrew and Syriac. When his patrons, the Afrighids, fell in 995, he moved between courts, trading letters with Avicenna that survive to this day.
In 1017 Mahmud of Ghazni conquered Khwarazm and carried off its scholars, possibly as captives, to Ghazni in present-day Afghanistan. Al-Biruni became court astrologer and, aged 44, went along on campaigns into the Indian subcontinent. What he learned there became his History of India, finished around 1030, admired for its even-handed account of Hindu belief and culture and earning him the title of The Master.
Of his 146 books, 95 dealt with astronomy, mathematics and related topics. He found that the Sun's apogee moves, contrary to Ptolemy, took the question of Earth's rotation seriously, and wrote a treatise on the astrolabe. His eclipse records were still useful in 1749, when Dunthorne used them to study the Moon's acceleration. He built a hydrostatic balance to measure the density of metals, gems and even air, and he dismissed astrological prediction while fully backing astronomy.
His cleverest experiment took place at Nandana, in present-day Pakistan. He measured the height of a hill, then how far the horizon dipped when viewed from its top, and used trigonometry to compute Earth's radius. How close he came depends on the length of his cubit, and since he knew nothing of atmospheric refraction, his answer could be off by around 20 percent. The method itself was brilliantly original. He died at Ghazni around 1050.
Source: Al-Biruni
