Arab navigation in the Indian Ocean before the coming of the Portuguese : being a translation of Kitāb al-Fawāʼid fī uṣūl al-baḥr waʼl-qawāʼid of Aḥmad b. Mājid al-Najdī ; together with an introduction on the history of Arab navigation, notes on the navigational techniques and on the topography of the Indian Ocean and a glossary of navigational terms / by G. R. Tibbetts.