The book’s principal purpose, however, is to instruct readers in the art of navigation, and though the author, an aged jurist with no practical experience, declined Philip III’s offer to appoint him chief pilot of the Spanish fleet, he did take on the theoretical responsibilities.
One notable inclusion is his proposal that to allow for differences in the location of the magnetic pole, tables of compass variations should be drawn up.
The only other copy recorded at auction is that in the Frank Streeter library, which at Christie’s New York in 2007 sold at $9000 (£4525). The copy sold at Dominic Winter (20% buyer’s premium) in South Cerney on January 30 just bettered that result at £4800.
In later plain boards, it was once part of Richard Heber’s great library, dispersed in 13 Sotheby’s sales in the years 1834-37.