▁II ▁of ▁Portugal ▁continued ▁this ▁effort , ▁forming ▁a ▁committee ▁on ▁navigation . ▁ ▁This ▁group ▁computed ▁tables ▁of ▁the ▁sun ' s ▁decl ination ▁and ▁improved ▁the ▁mar iner ' s ▁ast rol abe , ▁bel ieving ▁it ▁a ▁good ▁replacement ▁for ▁the ▁cross - st aff . ▁ ▁These ▁resources ▁improved ▁the ▁ability ▁of ▁a ▁navig ator ▁at ▁sea ▁to ▁judge ▁his ▁latitude . ▁Cast ilian ▁Jew ▁Abraham ▁Z ac ut , ▁the ▁author ▁of ▁an ▁exception al ▁treat ise ▁on ▁astronom y / astro log y ▁in ▁Heb rew , ▁with ▁the ▁title ▁Ha - j ib bur ▁Ha - g ad ol , ▁fled ▁to ▁Portugal ▁in ▁ 1 4 9 2 . ▁He ▁published ▁in ▁the ▁printing ▁press ▁of ▁Le i ria ▁in ▁ 1 4 9 6 , ▁the ▁book ▁Bi ur ▁Lu h oth , ▁or ▁in ▁Latin ▁Al man ach ▁Per pet u um , ▁which ▁was ▁soon ▁translated ▁into ▁Latin ▁and ▁Spanish . ▁In ▁this ▁book ▁were ▁the ▁astronom ical ▁tables ▁( e ph emer ides ) ▁for ▁the ▁years ▁ 1 4 9 7 ▁to ▁ 1 5 0 0 , ▁which ▁may ▁have ▁been ▁instrument al , ▁together ▁with ▁the ▁new ▁ast rol abe , ▁made ▁of ▁metal ▁and ▁not ▁wood ▁as ▁before ▁( created ▁and ▁perfect ed ▁at ▁the ▁beginning ▁of ▁the ▁Portuguese ▁discover ies ), ▁to ▁Vas co ▁da ▁G ama ▁and ▁Pedro ▁Ál var es ▁Cab ral ▁in ▁their ▁voy ages ▁to ▁India ▁( also ▁passing ▁through ▁South ▁America