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We have already stated that the astrolobe, which had been previously applied only to astronomical purposes, was accommodated to the use of mariners by Martin Behaim, towards the end of the fifteenth century. He was a scholar of Muller, of Koningsberg, better known under the name of Regiomontanus, who published the Almagest of Ptolemy.
The sea astrolobe, which is an instrument for taking the altitude of the sun, stars, &c., is described by Chaucer, in 1391, in a treatise on it, addressed to his little son, Louis; and Purchas informs us, that it was formerly applied only to astronomical purposes, but was accommodated to the use of seamen by Martin Behaim, at the command of John II., king of Portugal, about the year 1487.
The principal difficulty in ascertaining the latitude at sea, arose from the unsteady motion of the ship: to remedy this, several instruments were invented. We have already alluded to the astrolobe; but this, as well as the others, were imperfect and objectionable, till such time as Hadley's quadrant was invented, the principle and uses of which were first suggested by Newton.
He was succeeded by Werner, of Nuremberg, who published a translation of Ptolemy's Geography, with a commentary, in which he explains the method of finding the longitude at sea by the distance of a fixed star from the moon. The astronomical instruments hitherto used were, with the exception of the astrolobe, those which had been employed by Ptolemy and the Arabians.
Yea, blessed be alway a simple man who knows nothing but only his belief." In his little work "On the Astrolobe," Chaucer speaks with calm reasonableness of superstitions in which his spirit has no faith, and pleads guilty to ignorance of the useless knowledge with which they are surrounded.
It is not true, however, that he was the inventor of the astrolobe and the compass, or the first that put these instruments into the hands of navigators, though he undoubtedly was an excellent mathematician, and procured the best charts and instruments of the age: the use and application of these, he taught in the best manner to those he selected to command his ships.
That Magellan did not himself believe the strait was laid down in Behaim's chart from any authority is evident, from a circumstance mentioned by Pigafetta, who expressly informs us, that Magellan was resolved to prosecute his search after it to latitude 75°, had he not found it in latitude 52°. Now, as Behaim undoubtedly was the greatest cosmographer of the age, and had been employed to fit the astrolobe as a sea instrument, it is not to be supposed that, if he had good authority for the existence of a passage round South America, he would have left it in any chart he drew, with an uncertainty of 23 degrees.
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