structing the necessary instruments for navigation. He corrected the solar tables of the Arabs, and made some alterations in the astrolabe: For, strange to tell! the quadrant was not then known in Portugal, though, a hundred years before, Ulughbeg had measured the sun's height at Samarcand in Persia, with a quadrant of about 400 feet radius, the largest ever constructed, if, indeed, the size of this be not exaggerated.
Henry, who, by his liberality and affability, had drawn together the most learned mathematicians and ablest pilots of the age, now proposed to reduce his speculations to practice. Many ships had sailed in the course of his didquisitions, and ten years had now elapsed before the prince, after all his encouragement, could induce the captains to proceed farther than Cape Non, or, thirty leagues further, to Cape Bojador. To this their courage held good; after which, the fear of fiery oceans reviving in their minds, they returned exceedingly satisfied with their own perseverance and abilities. Henry, though greatly hurt at this behaviour, dissembled the low opinion which he had formed of both. He contented himself with proposing to them different reasons and rewards; and urged them to repeat their voyages, which, however, constantly ended in the same disappointment. And it is probable a much longer time might have been spent in these miscarriages, had not accident, or rather providence, stept in to his assistance.
John Gonsalez and Tristan Vaz, two gentlemen of his bed-chamber, seeing the impression this behaviour had made on the prince, and having obtained a small ship from him, resolved to double Cape Bojador, and discover the coast
