Towards the end of his ‘Book on the Measurement of the World’, written in, the Irish scholar Dcuil has a passage on the northernisles,including the Hebrides (where he himself had lived in his youth),the Orkneys,the Faroes and Iceland. Dcuil was one of many Irish scholarswho emigrated from Ireland and Scotland to the Carolingian empireto nd work and patronage. He wrote his account of world geographywhen he had already been living in Francia for manyyears. Hiscareerillustrates two contrary forces operating almost simultaneously in the lastyears of the eighth century and for much of the ninth: on the one hand,the closing in of the northern worldwith the advance of the Viking eetsand,on the other,the opportunities opening up on the continent. Thecombination of the two weakened intellectual life within Ireland and itsScottish outposts,though it is impossible to give any exact estimates ofthe decline.

Dícuil quoted the ancient geographer Solinus on the island calledThule, and went on to add something from his own knowledge. Thirty years before, that is about 795, he had been told by some clerics about the sun as seen from Thule at the summer solstice: