After _Henry_’s Decease, _Anno 1460._ the business of Navigation and Discoveries of new Countreys, lay neglected, because King _Alphonso_ turmoyl’d in a Civil War, his Crown being at stake, had not leisure to think or look after uncertain improvements by Sea; yet at last having quell’d his Enemies, he ventur’d forth some Ships, who Sail’d as far as the River _Zenaga_, and came to Anchor before the City of _Genny_, famous since for Trade, which gave its denomination to the Countrey and Coasts of _Guiny_, where they dealing, Barter’d for Ivory, Gold, Slaves, and also got so much footing into the Countrey, that they suddenly rais’d up a Fort, and Man’d it with a strong Garrison, Shipping their Slaves for _Lisbon_. _John_ the Second succeeding his Father _Alphonso_, had a great design upon _Arabia_ and _India_, and if possible, was ambitious to open a Passage from the _Atlantick_, to the _Oriental-Seas_. But the difficulty lay in Steering so often from sight of Land, venturing into the Main Ocean, obstructed by so many dangerous Shoals that lay so far out into the _Offin_. [Sidenote: For the Northern Constellations the _Astrolabe_ was in use long before.] At that time flourish’d three famous Mathematicians, _Rhoderick_, _Joseph_, and _Martin Bohemus_, Pupils bred up by _Joannes Monteregius_; with which the King consulting, perswaded, that they would by their Art invent some Instrument, that by Southern Constellations, the Pole being depress’d, the Navigator might know where he was, and in what height; so guessing what distance they were from this or that Countrey; they accordingly Club’d Learning, and by their great Study, found out what since hath prov’d so useful and beneficial to Seamen, the _Astrolabe_; which help having obtain’d, the Sailers encourag’d, more frequently ventur’d into remote and unknown Seas. [Sidenote: Remarkable passage of _Jaques Cano_.] [Sidenote: Discovery of _Congo_.] [Sidenote: _John_ the Second, seeks to discover _India_ by water.]