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 navigators who ventured into distant seas. The plane charts were fruitful sources of error and danger, owing to the degrees being shown in them as of equal length. Therefore the discovery of a method of projection which obviated these disadvantages marked a very great advance in the progress of the art of navigation. The discoverer was Gerard Cremer, better known as Mercator. Gerard learnt astronomy at Louvain from Gemma Frisius, published his first map in 1537, and constructed his great globe, two feet in diameter, in 1541. But the chart of the world, on the new projection, did not appear until 1569. The advantage of the system lies in the fact, as the author explains, that, although distances are distorted, the relative positions of places are correct. The actual chart is incorrectly drawn, and if Mercator really had a definite theory, he supplied others with no practical methods of working it out. The idea was not utilised in a scientific manner until Edward Wright of Garveston, in 1594, the year of Mercator's death, discovered the method of dividing the meridian. Five years later he published his treatise on 'The Correction of Certain Errors in Navigation,' and only thereafter did charts, on what is still nevertheless called Mercator's projection, come into general use.

Other valuable aids to the advancement of the science of navigation were furnished, in the sixteenth century, by the work of Pedro Nuñez, or Nonius, Martin Fernandez Enciso, Pedro de Medina, Martin Cortes, Bourne, William Borough, Blundeville, Hondius, Blagrave, Thomas Hood, Hues, Heriot, John Davis, and Gilbert of Colchester. Nonius gave the solution of several problems, including the determination of the latitude by the sun's double altitude, and was the first to introduce rhumb lines on charts. Enciso's 'Suma de Geografia' was the first practical navigation book for the use of sailors. Medina, though a Spanish writer, was the mentor of the early Dutch navigators. Cortes's 'Compendium' appeared in an English translation in 1561, and was used by John Davis, the navigator. Bourne's 'Regiment of the Sea' (1573) was the earliest original English work on Navigation, and contains the first account of the modern method of measuring a ship's run by means of the log and line, an apparatus which Bourne elsewhere says was the invention of one Humphrey Cole, of the Mint in the Tower. Borough wrote on the Magnet and Loadstone in 1581. Blundeville published his very popular 'Exercises' in 1594, with a table of meridianal parts as furnished to