The Porguese arrived in SÃ # o TomÃ Island on December 21 , 1471 and PrÃ ncipe Island on January 17 , 1492 . The dates of discovery are sometimes given as December 21 ( St Thomas 's Day ) , 1471 for SÃ # o TomÃ , and January 17 ( St Anthony 's Day ) , 1472 for PrÃ ncipe , though other sources give different nearby years .