498314 A Cross-Staff, illustration from \'A Seaman\'s Secrets\' by John Davis, published 1595 (woodcut) by English School, (16th century); Private Collection; (add.info.: John Davis (c.1550-1605) was one of Elizabeth I\'s top navigators and explorers. \'A Seaman\'s Secrets\' was a navigation manual. The Cross-staff, also known as Jacob\'s Staff, was a tool used in early celestial navigation. Inscribed "Are these all the rules that appertaine to the finding of the Poles height?"); English, out of copyright.