NavList:

I'm reading a book about Henry Hudson.  At one point in his 1607 voyage abord the Hopewell he claims to have determined latitude by the midnight sun.  He was in the high latitudes where the sun never sets and took his readings when the sun was at its lowest point in the sky.  Considering the instruments available to him in 1607 is this a reasonable thing to do?  He seems to have been using a simple cross staff and not the more modern three-vaned cross staff.  The technique was described in William Bourne's Regiment for the Sea in 1587.