[99] The “Genoese needle” is, of course, the mariner’s compass.—According to the “Mohit” of Admiral Sidi Ali ben Hosein (1554), published by Dr. Bittner and Dr. Tomascheck (Vienna, 1897), the pilots of the Indian Ocean determined relative latitudes by observing the altitudes of certain stars. The result was expressed, not in degrees as was done by the scientific astronomers of the day, but in _isbas_ or “fingers”, each equivalent to 1° 42´ 50”. The instrument which they used consisted of three staffs. Two of these were moveable on a hinge, and were directed respectively upon the horizon, and the star the altitude of which it was desired to determine. A third staff (or an octant) was fixed at the end of the horizon-staff, and upon it the angle observed could be read off. Vasco da Gama brought one of these instruments with him to Portugal, but the astronomer of Cabral’s expedition, who had been instructed to test its qualities, reported unfavourably (_Alguns documentos_, 1892, p. 122). Yet the results obtained by means of this instrument by the pilots of the Indian Ocean were very satisfactory, and the charts prepared by these very practical men were far more correct than the abortions produced by “scientific” Arab geographers. Parallels (at intervals of one-eighth of an _isba_) and meridians were marked upon these charts, and they were superior in this respect to the Portulani of the Mediterranean pilots. The meridians were probably drawn at intervals of _zams_, which were equal to one-eighth _isba_, or three hours’ sail, or nearly thirteen of our sea-miles. It is quite possible, as suggested by Dr. Bittner, that these pilots also invented the cross-staff, for _balhestilho_, the name by which this instrument became known in Portugal, is more likely to be derived from the Arabic _al-balista_ (altitude), than from the Latin _ballista_. Compare also Barros (_Dec. I_, liv. 4, c. 6), where an allusion is made to the instrument employed by the pilot who joined Vasco da Gama at Malindi. Barros says that the instrument consisted of three _taboas_ or plates. [100] This fruit is the coco-nut. [101] The sharifs (“nobles”) are the descendants of the Prophet, and although not “priests”, they enjoy a certain religious rank. Strictly speaking, this title can be claimed only by the head of the family which descends from the Prophet in a direct line. All others can only claim the title of _Saiyid_, Lord. The “white” Moors are, of course, true Arabs. [102] There are Government tanks now on the island, which are filled by the prisoners of Fort St. Sebastian. [103] _Agonia_, Arabic _El Jumbiyah_, a crooked poniard, worn in the waist-belt. [104] Barros calls these captives “Moors”, and the author himself does the same at a later stage of his Journal (see note, p. 37). [105] That is S. Jorge, and the small islet of S. Thiago, 1¾ miles to the south. [106] The text has 30th, but Saturday was the 31st.