The following post is by Mike Klein, a reference specialist in the Geography and Map Division.
Called the “father of temperature mapping,” the renowned German naturalist and climatologist, Alexander von Humboldt (1769-1859) devised the concept of the isotherm, which he described in 1816 as a “curve drawn through points on a globe which receive an equal quantity of heat.” Humboldt’s initial diagram map of average temperatures appeared in 1817 in an abstract of a much longer paper on isothermal lines published earlier that year. He was the first to recognize that isothermal lines cut through latitudes at different angles, thus disputing the prevailing scientific notion that climate depended solely on latitude.
Humboldt withheld publishing his idea in the form of a generalized world map while he waited for data from weather stations around the world. Thus, the isotherm concept remained virtually unknown outside of the broader scientific community until 1838, when it was given wider recognition on the map below. Titled Alexander von Humboldt’s System Der Isotherm-Kurven in Merkator’s Projection, it was published in Germany by Heinrich Berghaus in his Physikalischer Atlas, the first comprehensive physical world atlas.
Berghaus, a pioneer in scientific thematic cartography, authored numerous titles on humanistic and physical geography, as well as cartography. The 1845 edition of his Physikalischer Atlas included hundreds of beautifully engraved maps and illustrations pertaining to the earth and natural sciences, such as the one below, Die Isothermkurven Der Nordlichen Halbkugel, which illustrates climate over the northern hemisphere, and includes diagrams in the bottom corners depicting temperature and snow fall lines in relation to cross sections of mountain ranges in the Americas and Eurasia.
In spite of Berghaus’ achievement at disseminating one of Humboldt’s major theories, he was not the first to publish it on a world map. That role was assumed by a relatively unknown schoolteacher and geographic educator from Hartford, Connecticut, named William Channing Woodbridge (1794-1854), who in 1823 produced the item below, essentially the first world isothermal chart. The son of a minister and educator, Woodbridge was imbued with his father’s spirituality and passion for promoting the education of young women. Throughout his life he advocated for American educational reform, especially in the area of geography, co-authoring geography texts with fellow educational reformer, Emma Willard. His work with the deaf and disabled led him discover maps as an ideal vehicle for delivering information visually. Harboring an abiding interest in geography and natural history, Woodbridge was keen to introduce the latest geographical information into his maps.
Woodbridge also traveled to Europe to teach, as well as gather geographical ideas for his textbooks and atlases. While in Paris he met Humboldt, who introduced him to his concept of isotherms and demonstrated the ability to illustrate them diagrammatically. In somewhat of an innovation, Woodbridge expanded on Humboldt’s findings to publish his own world isothermal chart, in which he depicted the relationship between mean annual temperature and place, and illustrated climactic regions in color to indicate their suitability for agricultural commodities, while further indicating their potential ranges between latitudes. The chart, titled Isothermal Chart, or View of Climates & Production, Drawn from the Accounts of Humboldt & Others, was entered for copyright on January 15, 1823, in the state of Connecticut, probably with the local district court. The edition displayed here was included in Woodbridge’s School Atlas to Accompany Woodbridge’s Rudiments of Geography: Atlas on a New Plan . . ., published in 1830 in Hartford, Connecticut, to be used as an instructional device for school children.
Woodbridge’s chart, while intended only for use by a small audience, was something of a progenitor of the more complex and elaborate climate charts we see today. It may not be likely that Heinrich Berghaus was familiar with this initial attempt by a modest educator from Connecticut to depict global climate on a map, but it is obvious that after 1838, other publishers began taking advantage of Humboldt’s innovative theory and Woodbridge’s accessible chart to issue regional, national, and global climate charts on a more-or-less regular basis.