The year 1952 is the fourth centenary of the birth of Sir Walter Ralegh. So far from being the great romantic of tradition Sir Walter was a hard-headed practical man, and the first Englishman to engage a scientific and technical expert to advise him on his colonizing enterprises. He brought the brilliant young mathematician Thomas Hariot, some eight years his junior, direct from Oxford to Durham House, his mansion in the Strand, where, setting his instruments up on the leads, Hariot laboured for years at improving observational technique and revising the Ephemerides. Meanwhile he gave instruction in navigation to the officers of Ralegh's ships, himself obtaining practical experience on the voyage to Virginia in 1585, when he was able to observe the seaman's difficulties and the errors to which he was prone. He had already by 1584 written a new Instruction Manual which he entitled Arcticon, but this is unfortunately lost. We have, nevertheless, an epitome of its contents, for Ralegh asked for a ‘refresher course’ on the eve of his departure for Guiana, which was to take place in February 1595, and Hariot's teaching notes in his own (very crabbed) handwriting, besides fair copies of the tables he drew up, are now at the British Museum.