Four Instruments in Martín Cortés' Breve Compendio de la Sphera and a Rule for Finding the Age of the Moon
This paper investigates and discusses four instruments found in a sixteenth century Spanish book of navigation. The night clock is a rather standard application of similar instruments known since the fourteenth century in Europe. Cortés’ explanation of the causes of the deviation of the magnetic and geographical north is quite original. His instrument to correct for that the Polaris deviates from
