century 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 eqnal length. Therefore the discovery of a method of projection which obviated these dis- advantages marked a very great advance in the progress of the art of mvigation. The discoverer was Gerard Cremer, better known as Mercator. Gerard learnt astronomy at Louvain from Gemma Frisius, published his first map in 15:J?, and constructed his 'eat globe, two feet in diameter, in 1541. But the chart of the XVol'ld, off 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 ire correct. The acthal chart is incorrectly drawn, and if Mercator really had a definite theory, he snpplied others with no practical methods of working it ont. The idea was not utilised in a scientific manner nntil 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 CoTection of Certain En'ors in kN-avigation,' and .only thereafter did charts, on whtt is still nevertheless called Mercator's projection, come into general use.

Other yahtable aids to the advancement of the science of naviga- tion were furnished, in the sixteenth century, by the work of Pedro Nufiez, or 1q'onius, Martin Fernandez Enciso, Pedro de Medina, 5fartin Cortes, Bourne, hVillialn Borough, Blundeville, Hondius, Blai.q'ave, Thomas-Hood, Hues, Heriot, John Davis, and Gilbert of Colchester. Nonius gave the solution of several problems, including the dctmanination of the latitude by the sun's double altitude, and was the first to introduce rhmnb lines on charts. Enciso's Suma de Ge%,rafia' was the first practical navigation book for the use of sailors. Medina, though a Spanish writer, was the mentor of the early Dutch naxigators. Cort.es's 'Compendium' appeared in an English translation in 1561, and was used by J,hn Davis, the navigator. Bourne's 'liegimcnt of the Sea' (1573) was the earliest original English work on Navigation, and contains the first acconnt of the modern method of measuring a ship's rnn by means of the h)g and line, an apparatus n'hich Born'he elsewhere says was the invention of one Humlhrey Cole, of the Mint in the Tower. Borough wrote on the 15[agnet and Loadstone in 15,$1. Blundeville published his very p-l,ular 'Ex-

ercises' in 1594, with a table of meridianal parts as htrnished to