According to our calculations, then, the average distance covered in twelve hours with a fair breeze would be about seventy-five miles, and having obtained these important data we may now proceed to consider more particularly the unit of distance uniformly employed in the story of Wineland, namely the ‘dægr sigling’ or day’s sail. In its strictly scientific signification there can be no doubt that a ‘dægr’ is a period of twelve hours. The _Rímbegla_ (not the treatise already cited, but another incorporated in the same collection) is explicit upon the point. ‘In a day there are two “dægra”, in a “dægr” twelve hours’ (p. 6). In nautical phraseology, in which the word most commonly occurs, it cannot be denied that it is sometimes used with the same meaning. The passage already quoted, recording the voyage of Thorar Nefjolfson, is a case in point. On the other hand, the statement of the _Rímbegla_ treatise already cited, that there are ‘two tylfts in a “dægur” sailing’, must clearly be interpreted as meaning twenty-four hours, since even 120 nautical miles could not be covered in twelve hours at what we have found to be the extreme speed of an Icelandic sailing ship, and we should always hesitate to assume the identity of local or technical usage with accurate scientific terminology. One might, for example, be led seriously astray by taking the length of a mile from a geographical textbook and applying it under all circumstances to any distance called by the same name. The author of the last-mentioned passage in the _Rímbegla_ seems indeed to use ‘dægr’ and ‘dag’ interchangeably, for he goes on to say that ninety degrees of the earth’s circumference would take forty-five ‘dag siglingar’, and the complete circumnavigation of the globe would occupy 180 ‘dag siglingar’. If this passage stood alone it would doubtless be possible to explain the first ‘dægr’ as a mere verbal slip; it is accordingly necessary to examine the matter from a different standpoint, and to investigate the distances said to be covered by a given number of ‘dægra sigling’. A convenient passage for this purpose occurs in Landnáma I, 1. The writer is evidently endeavouring to fix the position of Iceland by reference to well-known points on all sides of it. With this object he makes the following statement: ‘Wise men say that from Norway from Stad it is seven “dægra” sail west to Horn on the east of Iceland; but from Snaefellsnes where the distance is shortest, there are four “dægra” of sea to Hvarf in Greenland[92].... From Reykjanes in the south of Iceland there are five “dægra” of sea to Jolduhlaup in Ireland, to the south, while from Langanes in the north of Iceland there are four “dægra” of sea to Svalbarda in the Polar Sea (Hafsbotn) and it is a “dægr” sail to the uninhabited parts of Greenland from Kolbein’s island (Mevenklint) north.’ Let us examine these statements seriatim.