This paper was first published in the Journal in 1954 (Vol. 7, p. 138). It is followed by comments from Michael Richey.

At the time (1542) when Jean Rotz presented Henry VIII with a variation compass, and an accompanying treatise on its making and use, the question of magnetic variation was an acute one. It formed part of a wider controversy concerning the general validity of the sea-chart which had been raised among seamen. As to this, Dr Pedro Nunez, writing a treatise in 1537 addressed to his friend and pupil the Infante Dom Luys of Portugal, said that there were skilled pilots who derided the chart and declared it to be ‘a mais falsa causa do mundo’ – the falsest thing in the world. Hastening to its defence, Nunez dealt at length with the navigating errors introduced by ignoring the convergence of the meridians, and showed besides that a rhumb, or line of constant bearing was a spiral curve on the globe.