Monday, March 7, 2011

Humboldt and Ritter

Collection: David Rumsey Historical Map Collection Author: Ziegler, J. M. Attributed Author: Ritter, Carl Date: 1864

Two of the founders of modern geography, Humboldt (1769-1859) and Karl Ritter (1779-1859), were associated with the great cartographic publishing house of Justus Perthes in Gotha. In 1806 Ritter, who was especially interested in geographic education, published a generalized map of Europe in which he rendered particular altitude zones by means of bands of gray decreasing in intensity with elevation. Although not strictly a hypsometric tint map Ritter's map systematically employs the convention by which the higher the altitude, the lighter the tone used. The opposite method-that is, increasing intensity of tone with elevation-had been employed in a very generalized hypsometric map of the world by Johan August Zeune (1778-1853) published in 1804. Later the Austrians Franz von Hauslaub (1798-1883) and Karl Peuker (1859-1940) developed the conventional layer (color) tint system now most commonly employed. This method, in which green is used for the lowest elevations followed by yellows at intermediate altitudes and brown at the highest peaks, was suggested by the humid European landscape and is not so suitable in all situations, especially mid- and low-latitude deserts.

Humboldt occupied a particularly influential position in the world of science in the first half of the nineteenth century. He was personally acquainted with many of the greatest thinkers of his time and became a statesman of science. Humboldt's early work was in mineralogy, chemistry, and botany, but later he embraced a wide range of knowledge, including physics, oceanography, and climatology, in his research. It was in the last of these fields of study that he made his most original contribution to cartography. But before devising his landmark map of isotherms (lines of equal average temperature), Humboldt journeyed extensively in the Americas with the French medical doctor and botanist Aime Bonpland. They were given permission to travel and to make scientific observations in the Spanish empire and left La Coruiia in 1799, when, ironically, Malaspina was languishing in jail in the same Spanish city. After his arrival in what is now Venezuela, Humboldt was able to confirm the existence of and to map the Casiquiare Channel, which connects Orinoco and Amazon drainage. Humboldt and Bonpland then went to Columbia and, via the Magdalena River, on to Ecuador, where they climbed nearly to the summit of Chimborazo (6,267 meters), believed to be the highest ascent by humans up to that time. More mapping was accomplished before they left for Mexico (New Spain), where Humboldt was impressed by the quality of training received by topographical engineers in the Viceroyalty, half of which was soon to be taken over by the United States. It was in Mexico City, with access to great archival resources, that Humboldt compiled his "Map of New Spain," the best delineation of Central and North America (from 15 to 40 degrees north latitude, and from 90 to 115 degrees west longitude) made up to that time, based on astronomical observations. On their way home to France in 1804 Humboldt and Bonpland visited President Jefferson in Washington, where, unwittingly, they provided cartographic intelligence on Mexico shortly to be of great value to the United States. Jefferson, following the Louisiana Purchase of 1803, had just dispatched Meriwether Lewis (1774-1809) and William Clark (1770-1838) overland to the Pacific Northwest in an exploration lasting from 1804 to 1806. Information from the sketch maps of these explorers was later incorporated into more general works such as Samuel Louis's "A Map of Lewis and Clark's Track, across the Western Portion of North America from the Mississippi to the Pacific Ocean," published in Philadelphia (1814).

Humboldt's map of New Spain was first published in France in 1811, but it is his isothermal map, resulting from his travels and observations on both sides of the Atlantic and published in 1817, that is his most enduring cartographic legacy. He had noted that the average temperatures on the west sides of continents in the midlatitudes are milder, by and large, than those on the east coasts in the same latitudes, an idea that overthrew the classical idea of a strict zonality of climate according to latitude. To demonstrate this important concept, he drew a plane chart from the equator to 85 degrees north latitude and from 94 degrees west longitude eastward to 120 degrees east longitude, based on the prime meridian of Paris. Within this framework, every tenth parallel from 0 to 70 degrees north is drawn, but only three meridians. The average summer and winter temperatures of thirteen places are plotted in their geographical locations, but there are no coastlines or other geographical data. To this base Humboldt added isotherms, which reach their highest latitude at 8 degrees east longitude while the lows are at 80 degrees west and 116 degrees east longitude (the three drawn meridians). The curving isothermal bands contrast with the straight geographical parallels of the plane chart. Below the map Humboldt added a diagram to show the effect of altitude on the isotherms. Humboldt acknowledged his debt to Halley for development of the isoline concept, which was soon applied to other phenomena.

Among his other contributions to geography, which Humboldt expressed in beautiful maps and diagrams, was his theory of the vertical zonation of climate and vegetation. In other words, if a mountain-even one at the equator, such as Chimborazo-is high enough, all plant associations from the tropics to near the polar regions could be represented among the mountain's vegetation. He also greatly improved on Kircher's conception of the surface ocean currents, one of which, the cool Peruvian current, bears Humboldt's name on some atlas maps to this day. This rich harvest of scientific ideas was popularized by others, especially Heinrich Berghaus (1797-1884) in his Physikalischer Atlas (Gotha, 1845), which contains maps that show average barometric pressure at sea level (isobars), average annual precipitation (isohyets), isotherms, and so forth. Biogeography was also represented in Berghaus's atlas with maps showing the distribution of crop plants, while in The Physical Atlas (Edinburgh, 1848) of the Scot Alexander Keith Johnston (1804-71) we find maps of selected fauna and of phytogeographic regions. The latter are derived from the research of the Dane Joakim Fredrick Schouw (1789-1852), but all of these workers looked-to Humboldt for inspiration.

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