University of Exeter. Retrieved 2010-02-21. ) 1 2 3 Beatrice Lumpkin (1997), Geometry Activities from Many Cultures, Walch Publishing, pp. 60 & 112–3, ISBN 0-8251-3285-1 ↑ Jim Al-Khalili, The Empire of Reason 2/6 (Science and Islam – Episode 2 of 3) on YouTube, BBC 1 2 3 4 Jim Al-Khalili, The Empire of Reason 3/6 (Science and Islam – Episode 2 of 3) on YouTube, BBC ↑ David A. King (1996), "Astronomy and Islamic society: Qibla, gnomics and timekeeping", in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, Vol.