app oint ed ▁at ▁his ▁failure ▁on ▁his ▁return ▁to ▁obtain ▁a ▁post ▁in ▁the ▁g ymnasium ▁of ▁his ▁native ▁Hamburg , ▁he ▁left ▁Germany ▁for ▁good . ▁Having ▁spent ▁two ▁years ▁from ▁ 1 6 2 2 ▁in ▁England , ▁at ▁Oxford ▁and ▁London , ▁gather ing ▁materials ▁for ▁his ▁Ge ograph i ▁Min ores , ▁he ▁then ▁proceeded ▁to ▁Paris . ▁ ▁At ▁Paris ▁in ▁ 1 6 2 4 , ▁he ▁became ▁li br arian ▁to ▁the ▁President ▁de ▁Mes mes , ▁the ▁friend ▁of ▁the ▁scholar ly ▁brothers ▁Dup uy , ▁and ▁the ▁correspond ent ▁of ▁N . ▁Pe ires c . ▁At ▁this ▁time ▁he ▁was ▁converted ▁to ▁Catholic ism . ▁He ▁was ▁probably ▁led ▁to ▁take ▁this ▁step ▁from ▁reading ▁the ▁writ ings ▁on ▁myst ical ▁the ology ▁of ▁the ▁Greek ▁and ▁Latin ▁F athers . ▁ ▁In ▁ 1 6 2 7 ▁he ▁went ▁to ▁Rome , ▁and ▁through ▁the ▁influence ▁of ▁Pe ires c ▁was ▁admitted ▁to ▁the ▁household ▁of ▁ ▁Card inal ▁Francesco ▁Bar ber ini , ▁former ▁pap al ▁nun cio ▁and ▁the ▁poss essor ▁of ▁the ▁most ▁important ▁private ▁library ▁in ▁Rome . ▁In ▁ 1 6 3 6 ▁he ▁became ▁the ▁cardinal ' s ▁li br arian . ▁Much ▁of ▁Hol sten ius ' ▁collection ▁was ▁depos ited ▁in ▁the ▁Bibli oteca ▁Angel ica ▁in ▁Rome . ▁ ▁Finally , ▁under ▁ ▁In noc ent ▁X , ▁he ▁was ▁placed ▁in ▁charge ▁of ▁the ▁V at ican ▁Library . ▁The ▁pop