166 MAPS AND THEIR MAKERS 



magnetic declination. His celebrated 'General chart', with its 

 *Halleyan lines', published in 1701, was an important contri- 

 bution to the study of terrestrial magnetism. 



Some have seen in the maps of John Rocque, with their 

 distinction between arable, pasture and wood, the forerunners 

 of the 'land use' maps of today. At the beginning of the nine- 

 teenth century, maps were being used systematically in the 

 new science of geology. William Smith, a pioneer in the 

 science, using fossils to arrange the strata chronologically, had 

 initiated the geological mapping of England and Wales. His 

 'Delineation of the strata of England and Wales with part of 

 Scotland', in fifteen sheets on a scale of five miles to one inch, 

 was engraved and published by John Gary in 1815, with the 

 geological data hand-coloured; the work was placed on a 

 permanent footing by the establishment of the Geological 

 Survey in 1835, which used the Ordnance Survey One Inch 

 sheets as a base. 



It was however the foundation in Germany of geography 

 as a modern study which demonstrated the use of the maps as 

 instruments for specialized research. Both Alexander von 

 Humboldt and Karl Ritter appreciated their value in under- 

 standing the distribution and inter-relation of phenomena on 

 the earth's surface, when they advanced the principle of 

 causality as the mainspring of geographical research. Humboldt 

 in particular showed that cartographically a great variety of 

 facts could be represented in an orderly and readily intelligible 

 manner. The voluminous results of his travels and studies in 

 New Spain were accompanied by an 'Atlas geographique et 

 physique', 1812, in which the beginning of this development 

 is apparent. The device of isotherms, or lines of equal tempera- 

 ture is due to him, and he also mapped the areal and altitudinal 

 limits of plants and other phenomena. 



His ideas were developed enthusiastically by several 

 disciples, whose work was presented to the general public by 

 the celebrated establishment of Justus Perthes at Gotha. 

 One of these was Adolf Stieler, who, after practical experience 

 in survey, came forward with a somewhat grandiose plan for a 

 general atlas. His specifications included a convenient format; 

 text to accompany each map; the greatest possible accuracy, 



