138 MAPS AND THEIR MAKERS 



The solution of the problem now generally employed is the 

 contour line, i.e. a line running through all points at a given 

 elevation. Unlike the hachure, it runs along, and not down, 

 the slope. The origin of contouring is still somewhat obscure. 

 An obvious contour is the line of high or low water, and it is 

 not surprising therefore that it appears to have been developed 

 in the Netherlands, at first to show the configuration of the 

 sea bottom. Soundings off coasts and in estuaries are common 

 on charts of the sixteenth century, on which banks are also 

 enclosed by broken lines. It would not be a great step in advance 

 to run these lines through soundings indicating a given depth 

 of water. This appears to have been the practice by the begin- 

 ning of the eighteenth century, by which time the number of 

 soundings had greatly increased. 



On a map of the Merwede estuary (1729), N. S. Cruquius, 

 a Dutch engineer, showed depths by lines of equal soundings, 

 referred to a common datum. Soon after, Philippe Buache 

 drew a bathymetric map of the English Channel, with under- 

 water contours at intervals of ten fathoms, but this map was 

 not published in the Memoires of the Paris Academy until 

 1752. In 1737 he had submitted to the Academy a chart of 

 Femao da Noronha with submarine contours, accompanied 

 by a vertical section across an off-lying bank. Since he was 

 also engaged in levelling operations in Paris, he must have 

 recognized the applicability of the contour method to land 

 surfaces. Its first use on land however is usually credited to 

 Milet de Mureau, who about 1749 used lines of equal altitude 

 on his plans of fortifications. 



The eighteenth century was a period of great activity in 

 the construction of canals, and it is therefore quite probable 

 that the engineers responsible for them discovered the principle 

 independently, just as Charles Hutton did in 1777 when seeking 

 a method to determine the mass of Schiehallion, a mountain 

 in Scotland. The general use in maps of large areas was delayed 

 by the lack of sufficient data, though Cassini and others in 

 France had calculated some heights by triangulation and by 

 the barometer. The earliest British map to include spot heights 

 appears to be Christopher Packe's Thysico-chorographical 

 chart' of Kent, 1743. Packe obtained his altitudes by the 



