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Jean Rotz and the Marine Chart, 1542

Published online by Cambridge University Press:  18 January 2010

Extract

At the time (1542) when Jean Rotz presented Henry VIII with a variation compass, and an accompanying treatise1 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 Nuñez, 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, Nuñez 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. He dealt only incidentally with the variation of the compass needle and how to measure it, and this may explain why Rotz made this second source of error his main theme. The parallel N.–S. lines and E.–W. lines of the compass roses making a rectangular net on the chart are completely misleading, he says, for only the ‘diametral line’ (agonic line, line of no variation) actually runs through the poles of the world, the others lie at angles one with the other according to the magnetic variation.

Type
Research Article
Copyright
Copyright © The Royal Institute of Navigation 1954

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References

REFERENCES

1 Taylor, E. G. R. (1954). Jean Rotz and the variation of the compass, 1542. This Journal, 7, 9.Google Scholar
2 Taylor, E. G. R. (1951). The oldest Mediterranean pilot. This Journal, 4, 81.Google Scholar
3 Barbosa, A. (1948). Novos subsidies para a historia da ciencia nautica portuguesa da época dos docobrimentos. Porto: Instituto para a alta cultura. (Use has been made of extensive quotations in this work from originals not otherwise available.)Google Scholar