It is comparatively easy to see how such a discrepancy in nautical use may have arisen. Evidently ‘dægr sigling’ was the usual nautical expression for a day’s sail. This is shown not only by the fact that it is nearly always in a nautical context that the word ‘dægr’ makes its appearance, but also by the opening sentence of the Landnámabók’s preface, which renders Bede’s words ‘sex dierum navigatione’ by ‘sex dægra sigling’ as the obvious equivalent. Now of course until the exodus brought about in Scandinavia by the policy of Harold Haarfagre, the vast majority of the voyages undertaken by Norsemen were along the coast of Norway and the adjacent countries, and were carried on almost entirely by day, the ships putting into a convenient haven almost every night. The coast of Norway, before the days of lighthouses, cannot have been a pleasant place to navigate in the dark, and in fact we almost always find it recorded, as an exceptional occurrence, when any motive induced the seamen of this period to sail day and night without stopping. A day’s journey in a ship would therefore in the normal course be equivalent to the distance covered in a ‘dægr’ of twelve hours, and thus the application of this word to a nautical day’s journey doubtless began. Then, when colonial expansion and viking enterprises made continuous open-sea voyages more common, two courses would be open to those who wished to record the distance travelled. They might take the nautical expression ‘dægr’ as referring to the twelve hours actually occupied in sailing under old conditions, or they might take it as extending to the period during which the ships of less venturous seamen had usually lain at anchor. A man who had taken—say—four ‘dægra’ to sail between two points, stopping at night, would actually have travelled but forty-eight hours, but the time occupied from point to point would have been four days of twenty-four hours. According to the aspect of the question which struck a sailor accustomed to this method of reckoning he would be likely to call a continuous voyage of four days either four or eight ‘dægra’. Thus a variety in local usage might quite naturally spring up which would account for the discrepancy which has given rise to the difficulties with which I have been endeavouring to deal.