This it certainly was not in Latini's time. "No mariner could use it (the polarized magnet), nor would sailors venture themselves to sea ... with an instrument so like one of infernal make." In the latter part of the thirteenth century, and not before, its use seems to have crept in among Mediterranean pilots and captains, and in the course of the fourteenth century it was almost universally accepted.
A mistake has been made on one point. The first scientific (or portolano) type of map is generally associated with the first scientific use of the magnet; but portolani began while men had not advanced beyond the use of the primitive water-compass above described; and "accurate determination by means of this" must have been very difficult on a tossing sea. "A comparison of the contours of the Mediterranean, according to various portolanos, with a modern chart, shows that the normal portolano contained no mistake due to the misdirection of the compass."[[293]] Nor do the earliest portolani contain any compass-roses or wind-roses. Gradually these were introduced into the new charts, e.g., they are found in the Catalan Atlas of 1375, in the Pinelli of 1384, and in many fifteenth-century portolani; but not till the sixteenth century do we have a number of these roses drawn on the same map-sheet.
The use of the quadrant by Prince Henry and his sailors is expressly mentioned by Diego Gomez; but neither in this case, nor in that of the compass, are we warranted in assuming (as some authorities have done) that to the Infant is due the first use of astronomical instruments at sea.
C. Raymond Beazley.
13, The Paragon, Blackheath.
March 27th, 1899.
Facsimile of Prince Henry's Initial Signature.
[I. D. A. = Iffante Dom Anrique.
[236] E.g., the Peutinger Table.
[237] Viz., before the end of the thirteenth century; see Dawn of Modern Geography, ch. vi, on "Geographical Theory in the Earlier Middle Ages," and especially pp. 273-284, 327-340, 375-391.
[238] E.g., in the Carte Pisane and the work of Giovann de Carignano.