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John Seller
Practical Navigation: or, an Introduction to the Whole Art. Containing The Doctrine of Plain and Spherical Triangles. Plain, Mercator, Great-Circle Sailing; and Astronomical Problems . . .
London, 1694
Slaughter 3003

By 1694, this popular handbook on practical navigation was in its seventh edition. The book aimed to introduce the necessary mathematical skills for ocean navigation, which required the ability to steer by the angle of the stars, sun, planets, etc., and to determine latitude and longitude in ocean waters far from visible landmarks. Even today one is daunted by the tables of logarithms, sines, tangents, and secants that fill this book.

Appointed Hydrographer to the King, Charles II, in 1671, Seller here continues to list himself as Hydrographer to the King, now William III.

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EPO, 1998