54 
THE VOYAGE OF H.M.S. CHALLENGER. 
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Hydrographic 
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tenth degree south latitude, at the horizon of Nuremberg. But a more important modifi- 
cation w ii introduced by 0. Mercator, who, towards the middle of the sixteenth century, 
invented his web-known method of representing the whole surface in true bearings, which 
was destined to render such signal services to navigation. 1 The researches of Ed. Wright, 
relating to the theory and construction of these charts," and those of Henry Bond and 
Gregory (1668). added to the advantages this method offered to navigators. This carto- 
graphic process was created at a time when marine charts w r ere far from being complete. 
Henceforth it was no longer necessary to trouble about finding a system of projection, 
and attention could be devoted to improving the charts in all points useful to mariners. 
Although the science of geography made rapid advances, owing to the great voyages 
of discovery, still the progress of those branches of geodesy relating to map-making was 
slow. Distinct advances, however, are to be observed in the Cosmographia of Sebastian 
Munster as early as 1544, and in the triangulation of Snellius in 1615. The methods 
already known for determining longitudes were developed, while other methods were 
invented and when the astrolabe was replaced by the sextant (octant), invented, it has 
been said, by Newton about 1700 and quite independently by Hadley in 1731, mariners 
possessed the means of establishing the position of places with tolerable accuracy. 3 
The seventeenth century was a remarkable period for astronomical and mathematical 
studies, on which the exact knowledge of the globe rests, and by the end of that century 
sufficiently numerous astronomical observations had been made to determine the position 
of many points on the earth’s surface, and hence to allow of the errors in the charts 
b< ::ig rectified. The great French geographer, Guillaume Delisle, undertook this herculean 
to. -k and his work was continued by Bourguignon d’Anville, who w r as 29 years of age 
when Delisle died in 1726. D’Anville was superior to his predecessor, especially as 
regards workmanship. 
Pn gress v. as soon manifest in the indication of depths, hydrographic signs, the first 
meridian, the scale, the orthography, the type, &c. As to hydrographic signs, crosses 
were used to show reefs and rocky bottoms ; sandbanks and shallows were marked with 
dotted lines or masses of dots ; other hydrographic signs were introduced at a later 
period. Marine charts, as compared with land maps, present some differences. In marine 
chart- t lie -ca i- left white, the coasts alone are distinctly marked, and the mountains 
inland arc only represented when of sendee to the mariner for finding out his bearings ; 
on the sea rea are shown the soundings, the shallows, the currents, the tides, the 
c mp -s, See. Even at an early period note was taken of the nature and the colour of 
the bottom of the sea, for these characteristics might be of service to seamen in a fog 
as denoting the approach to land. 
• M< ttor’a imp «.n thin increasing cylindrical projection was first published in 1569. 
* Certain Error* in Navigation, London, 1610. 
Tin sextant was also invented independently by Godfrey of Philadelphia in 1730. 
