Everyone knows that longitude is the distance east or west of a given meridian. In those days Greenwich did not enter into the matter: the observatory there had still to be founded. When Davis wrote in the year 1594 there was no variation at St. Michael’s in the Azores, and so the longitude was reckoned from there. “Longitude,” he defines, “is that portion of the Equator contained betweene the Meridian of S. Michel’s, one of the Assores, and the Meridian of the place whose longitude is desired: the reason why the accompt of longitude doth begin at this Ile is, because that there the compasse hath no variety.” Be it remembered, also, that it was Davis who improved the cross-staff and superseded the clumsy astrolabe for taking meridian altitudes at sea. It was commonly spoken of as Davis’s quadrant, and was afterwards improved by Flamstead with the addition of a glass lens. Subsequently it was further improved by Halley, and as such was used almost exclusively till the year 1731, when it was in turn superseded by Halley’s quadrant. When we read again the entrancing narratives given in Hakluyt and elsewhere of the Elizabethan voyages into the unknown, let us note that reposing somewhere in the high poop of these ships there were most probably all the following instruments for navigating the trackless seas. There was a calendar, an astrolabe, a cross-staff, a celestial globe, a terrestrial globe, a universal horloge for knowing the hour of the day in every latitude, a nocturne labe for telling the hour of the night, one or more compasses, a navigation chart, a general map, and a printed chart. [Illustration: SHIP DESIGNER WITH HIS ASSISTANT. This illustration belongs to the latter half of the sixteenth century, or the beginning of the seventeenth, and is among the Pepysian MSS. in Magdalene College, Cambridge. Pepys’ own title for this is “Fragments of Ancient English Shipwrightry.”] It was in 1599 that Edward Wright published his “Haven-finding Art.” In his volume “Certaine Errors in Navigation,” he complains of the errors in the proportions of the existing charts. These consisted in wrongly showing the distances of places. He speaks also of sailing “by a great Circle, which is to bee drawne by those two places,” and asserts that this is a better method than sailing always at right angles to the meridian. In practically all the charts of this age the surface was ruled with rhumb-lines from the thirty-two points of the compass, as is still the case to-day on certain Dutch charts. The origin of the word “rhumb” was Portuguese, and doubtless these lines appeared on the earliest Portuguese charts. In the first of these two books, Wright also furnished a table of variations of the compass in different parts of the world.