Alexander von Humboldt

With the financial resources to finance his scientific travels, he sought a ship on a major expedition. Meantime, he went to Paris, where his brother Wilhelm was now living. Paris was a great center of scientific learning and his brother and sister-in-law Caroline were well connected in those circles. Louis-Antoine de Bougainville urged Humboldt to accompany him on a major expedition, likely to last five years, but the French revolutionary Directoire placed Nicolas Baudin at the head of it rather than the aging scientific traveler.[37] On the postponement of Captain Baudin's proposed voyage of circumnavigation due to continuing warfare in Europe, which Humboldt had been officially invited to accompany, Humboldt was deeply disappointed. He had already selected scientific instruments for his voyage. He did, however, have a stroke of luck with meeting Aimé Bonpland, the botanist and physician for the voyage.

Discouraged, the two left Paris for Marseilles, where they hoped to join Napoleon Bonaparte in Egypt, but North Africans were in revolt against the French invasion in Egypt and French authorities refused permission to travel. Humboldt and Bonpland eventually found their way to Madrid, where their luck changed spectacularly.[38]

Charles IV of Spain who authorized Humboldt's travels and research in Spanish America

In Madrid, Humboldt sought authorization to travel to Spain's realms in the Americas; he was aided in obtaining it by the German representative of Saxony at the royal Bourbon court. Baron Forell had an interest in mineralogy and science endeavors and was inclined to help Humboldt.[38] At that time, the Bourbon Reforms sought to reform administration of the realms and revitalize their economies.[39] At the same time, the Spanish Enlightenment was in florescence. For Humboldt "the confluent effect of the Bourbon revolution in government and the Spanish Enlightenment had created ideal conditions for his venture".[40]

The Bourbon monarchy had already authorized and funded expeditions, with the Botanical Expedition to the Viceroyalty of Peru to Chile and Peru (1777–88), New Granada (1783–1816), New Spain (Mexico) (1787–1803), and the Malaspina Expedition (1789–94). These were lengthy, state-sponsored enterprises to gather information about plants and animals from the Spanish realms, assess economic possibilities, and provide plants and seeds for the Royal Botanical Garden in Madrid (founded 1755).[41] These expeditions took naturalists and artists, who created visual images as well as careful written observations as well as collecting seeds and plants themselves.[42] Crown officials as early as 1779 issued and systematically distributed Instructions concerning the most secure and economic means to transport live plants by land and sea from the most distant countries, with illustrations, including one for the crates to transport seeds and plants.[43]

When Humboldt requested authorization from the crown to travel to Spanish America, most importantly, with his own financing, it was given positive response. Spain under the Habsburg monarchy had guarded its realms against foreigner travelers and intruders. The Bourbon monarch was open to Humboldt's proposal. Spanish Foreign Minister Don Mariano Luis de Urquijo received the formal proposal and Humboldt was presented to the monarch in March 1799.[38] Humboldt was granted access to crown officials and written documentation on Spain's empire. With Humboldt's experience working for the absolutist Prussian monarchy as a government mining official, Humboldt had both the academic training and experience of working well within a bureaucratic structure.[40]

Portrait of Alexander von Humboldt by Friedrich Georg Weitsch, 1806

Before leaving Madrid in 1799, Humboldt and Bonpland visited the Natural History Museum, which held results of Martín de Sessé y Lacasta and José Mariano Mociño's botanical expedition to New Spain.[44] Humboldt and Bonpland met Hipólito Ruiz López and José Antonio Pavón y Jiménez of the royal expedition to Peru and Chile in person in Madrid and examined their botanical collections.[45]

Humboldt and Aimé Bonpland were in the Amazon rainforest by the Casiquiare River, with their scientific instruments, which enabled them to take many types of accurate measurements throughout their five-year journey. Oil painting by Eduard Ender, 1856.

Map of the Cassiquiare canal based on Humboldt's 1799 observations

Armed with authorization from the King of Spain, Humboldt and Bonpland made haste to sail, taking the ship Pizarro from A Coruña, on 5 June 1799. The ship stopped six days on the island of Tenerife, where Humboldt climbed the volcano Teide, and then sailed on to the New World, landing at Cumaná, Venezuela, on 16 July.

The ship's destination was not originally Cumaná, but an outbreak of typhoid on board meant that the captain changed course from Havana to land in northern South America. Humboldt had not mapped out a specific plan of exploration, so that the change did not upend a fixed itinerary. He later wrote that the diversion to Venezuela made possible his explorations along the Orinoco River to the border of Portuguese Brazil. With the diversion, the Pizarro encountered two large dugout canoes each carrying 18 Guayaqui Indians. The Pizarro's captain accepted the offer of one of them to serve as pilot. Humboldt hired this Indian, named Carlos del Pino, as a guide.[46]

Venezuela from the 16th to the 18th centuries was a relative backwater compared to the seats of the Spanish viceroyalties based in New Spain (Mexico) and Peru, but during the Bourbon reforms, the northern portion of Spanish South America was reorganized administratively, with the 1777 establishment of a captaincy-general based at Caracas. A great deal of information on the new jurisdiction had already been compiled by François de Pons, but was not published until 1806.[40][47]

Rather than describe the administrative center of Caracas, Humboldt started his researches with the valley of Aragua, where export crops of sugar, coffee, cacao, and cotton were cultivated. Cacao plantations were the most profitable, as world demand for chocolate rose.[48] It is here that Humboldt is said to have developed his idea of human-induced climate change. Investigating evidence of a rapid fall in the water level of valley's Lake Valencia, Humboldt credited the desiccation to the clearance of tree cover and to the inability of the exposed soils in retain water. With their clear cutting of trees, the agriculturalists were removing the woodland's "threefold" moderating influence upon temperature: cooling shade, evaporation and radiation.[49]

Humboldt visited the mission at Caripe and explored the Guácharo cavern, where he found the oilbird, which he was to make known to science as Steatornis caripensis. Also described the Guanoco asphalt lake as "The spring of the good priest" ("Quelle des guten Priesters").[50][51] Returning to Cumaná, Humboldt observed, on the night of 11–12 November, a remarkable meteor shower (the Leonids). He proceeded with Bonpland to Caracas where he climbed the Avila mount with the young poet Andrés Bello, the former tutor of Simón Bolívar, who later became the leader of independence in northern South America. Humboldt met the Venezuelan Bolívar himself in 1804 in Paris and spent time with him in Rome. The documentary record does not support the supposition that Humboldt inspired Bolívar to participate in the struggle for independence, but it does indicate Bolívar's admiration for Humboldt's production of new knowledge on Spanish America.[52]

In February 1800, Humboldt and Bonpland left the coast with the purpose of exploring the course of the Orinoco River and its tributaries. This trip, which lasted four months and covered 1,725 miles (2,776 km) of wild and largely uninhabited country, had an aim of establishing the existence of the Casiquiare canal (a communication between the water systems of the rivers Orinoco and Amazon). Although, unbeknownst to Humboldt, this existence had been established decades before,[53] his expedition had the important results of determining the exact position of the bifurcation,[18] and documenting the life of several native tribes such as the Maipures and their extinct rivals the Atures (several words of the latter tribe were transferred to Humboldt by one parrot[54]). Around 19 March 1800, Humboldt and Bonpland discovered dangerous electric eels, whose shock could kill a man. To catch them, locals suggested they drive wild horses into the river, which brought the eels out from the river mud, and resulted in a violent confrontation of eels and horses, some of which died. Humboldt and Bonpland captured and dissected some eels, which retained their ability to shock; both received potentially dangerous electric shocks during their investigations. The encounter made Humboldt think more deeply about electricity and magnetism, typical of his ability to extrapolate from an observation to more general principles.[55] Humboldt returned to the incident in several of his later writings, including his travelogue Personal Narrative (1814–29), Views of Nature (1807), and Aspects of Nature (1849).[56]

Two months later, they explored the territory of the Maypures and that of the then-recently extinct Aturès Indians. Humboldt laid to rest the persistent myth of Walter Raleigh's Lake Parime by proposing that the seasonal flooding of the Rupununi savannah had been misidentified as a lake.[57]

Humboldt botanical drawing published in his work on Cuba

On 24 November 1800, the two friends set sail for Cuba, landing on 19 December,[58] where they met fellow botanist and plant collector John Fraser.[59] Fraser and his son had been shipwrecked off the Cuban coast, and did not have a license to be in the Spanish Indies. Humboldt, who was already in Cuba, interceded with crown officials in Havana, as well as giving them money and clothing. Fraser obtained permission to remain in Cuba and explore. Humboldt entrusted Fraser with taking two cases of Humboldt and Bonpland's botanical specimens to England when he returned, for eventual conveyance to the German botanist Willdenow in Berlin.[60] Humboldt and Bonpland stayed in Cuba until 5 March 1801, when they left for the mainland of northern South America again, arriving there on 30 March.

Humboldt is considered to be the "second discoverer of Cuba" due to the scientific and social research he conducted on this Spanish colony. During an initial three-month stay at Havana, his first tasks were to properly survey that city and the nearby towns of Guanabacoa, Regla, and Bejucal. He befriended Cuban landowner and thinker Francisco de Arango y Parreño; together they visited the Guines area in south Havana, the valleys of Matanzas Province, and the Valley of the Sugar Mills in Trinidad. Those three areas were, at the time, the first frontier of sugar production in the island. During those trips, Humboldt collected statistical information on Cuba's population, production, technology and trade, and with Arango, made suggestions for enhancing them. He predicted that the agricultural and commercial potential of Cuba was huge and could be vastly improved with proper leadership in the future.

On their way back to Europe from Mexico on their way to the United States, Humboldt and Bonpland stopped again in Cuba, leaving from the port of Veracruz and arriving in Cuba on 7 January 1804, staying until 29 April 1804. In Cuba, he collected plant material and made extensive notes. During this time, he socialized with his scientific and landowner friends, conducted mineralogical surveys, and finished his vast collection of the island's flora and fauna that he eventually published as Essai politique sur l'îsle de Cuba.[61]

Humboldt and his fellow scientist Aimé Bonpland near the foot of the Chimborazo volcano, painting by Friedrich Georg Weitsch (1810)

After their first stay in Cuba of three months, they returned to the mainland at Cartagena de Indias (now in Colombia), a major center of trade in northern South America. Ascending the swollen stream of the Magdalena River to Honda, they arrived in Bogotá on 6 July 1801, where they met the Spanish botanist José Celestino Mutis, head of the Royal Botanical Expedition to New Granada, staying there until 8 September 1801. Mutis was generous with his time and gave Humboldt access to the huge pictorial record he had compiled since 1783. Mutis was based in Bogotá, but as with other Spanish expeditions, he had access to local knowledge and a workshop of artists, who created highly accurate and detailed images. This type of careful recording meant that even if specimens were not available to study at a distance, "because the images traveled, the botanists did not have to".[62] Humboldt was astounded at Mutis's accomplishment; when Humboldt published his first volume on botany, he dedicated it to Mutis "as a simply mark of our admiration and acknowledgement".[63]

Humboldt had hopes of connecting with the French sailing expedition of Baudin, now finally underway, so Bonpland and Humboldt hurried to Ecuador.[61] They crossed the frozen ridges of the Cordillera Real, they reached Quito on 6 January 1802, after a tedious and difficult journey.

Their stay in Ecuador was marked by the ascent of Pichincha and their climb of Chimborazo, where Humboldt and his party reached an altitude of 19,286 feet (5,878 m). This was a world record at the time, but 1000 feet short of the summit.[64] Humboldt's journey concluded with an expedition to the sources of the Amazon en route for Lima, Peru.[65]

At Callao, the main port for Peru, Humboldt observed the transit of Mercury on 9 November and studied the fertilizing properties of guano, rich in nitrogen, the subsequent introduction of which into Europe was due mainly to his writings.[18]

Silver mining complex of La Valenciana, Guanajuato, Mexico

Basalt prisms at Santa María Regla, Mexico by Alexander von Humboldt, published in Vue des Cordillères et monuments des peuples indigènes de l'Amérique

Aztec calendar stone

Dresden Codex, later identified as a Maya manuscript, published in part by Humboldt in 1810

Humboldt and Bonpland had not intended to go to New Spain, but when they were unable to join a voyage to the Pacific, they left the Ecuadorian port of Guayaquil and headed for Acapulco on Mexico's west coast. Even before Humboldt and Bonpland started on their way to New Spain's capital on Mexico's central plateau, Humboldt realized the captain of the vessel that brought them to Acapulco had reckoned its location incorrectly. Since Acapulco was the main west-coast port and the terminus of the Asian trade from the Spanish Philippines, having accurate maps of its location was extremely important. Humboldt set up his instruments, surveying the deep-water bay of Acapulco, to determine its longitude.[66][67]

Humboldt and Bonpland landed in Acapulco on 15 February 1803, and from there they went to Taxco, a silver-mining town in modern Guerrero. In April 1803, he visited Cuernavaca, Morelos. Impressed by its climate, he nicknamed the city the City of Eternal Spring.[68][69] Humboldt and Bonpland arrived in Mexico City, having been officially welcomed via a letter from the king's representative in New Spain, Viceroy Don José de Iturrigaray. Humboldt was also given a special passport to travel throughout New Spain and letters of introduction to intendants, the highest officials in New Spain's administrative districts (intendancies). This official aid to Humboldt allowed him to have access to crown records, mines, landed estates, canals, and Mexican antiquities from the prehispanic era.[70] Humboldt read the writings of Bishop-elect of the important diocese of Michoacan Manuel Abad y Queipo, a classical liberal, that were directed to the crown for the improvement of New Spain.[71]

They spent the year in the viceroyalty, traveling to different Mexican cities in the central plateau and the northern mining region. The first journey was from Acapulco to Mexico City, through what is now the Mexican state of Guerrero. The route was suitable only for mule train, and all along the way, Humboldt took measurements of elevation. When he left Mexico a year later in 1804, from the east coast port of Veracruz, he took a similar set of measures, which resulted in a chart in the Political Essay, the physical plan of Mexico with the dangers of the road from Acapulco to Mexico City, and from Mexico City to Veracruz.[72] This visual depiction of elevation was part of Humboldt's general insistence that the data he collected be presented in a way more easily understood than statistical charts. A great deal of his success in gaining a more general readership for his works was his understanding that "anything that has to do with extent or quantity can be represented geometrically. Statistical projections [charts and graphs], which speak to the senses without tiring the intellect have the advantage of bringing attention to a large number of important facts".[73]

Humboldt was impressed with Mexico City, which at the time was the largest city in the Americas, and one that could be counted as modern. He declared "no city of the new continent, without even excepting those of the United States, can display such great and solid scientific establishments as the capital of Mexico".[74] He pointed to the Royal College of Mines, the Royal Botanical Garden and the Royal Academy of San Carlos as exemplars of a metropolitan capital in touch with the latest developments on the continent and insisting on its modernity.[75] He also recognized important creole savants in Mexico, including José Antonio de Alzate y Ramírez, who died in 1799, just before Humboldt's visit; Miguel Velásquez de León; and Antonio de León y Gama.[71]

Humboldt spent time at the Valenciana silver mine in Guanajuato, central New Spain, at the time the most important in the Spanish empire.[76] The bicentennial of his visit in Guanajuato was celebrated with a conference at the University of Guanajuato, with Mexican academics highlighting various aspects of his impact on the city.[77] Humboldt could have simply examined the geology of the fabulously rich mine, but he took the opportunity to study the entire mining complex as well as analyze mining statistics of its output. His report on silver mining is a major contribution, and considered the strongest and best informed section of his Political Essay. Although Humboldt was himself a trained geologist and mining inspector, he drew on mining experts in Mexico. One was Fausto Elhuyar, then head of the General Mining Court in Mexico City, who, like Humboldt was trained in Freiberg. Another was Andrés Manuel del Río, director of Royal College of Mines, whom Humboldt knew when they were both students in Freiberg.[78] The Bourbon monarchs had established the mining court and the college to elevate mining as a profession, since revenues from silver constituted the crown's largest source of income. Humboldt also consulted other German mining experts, who were already in Mexico.[71] While Humboldt was a welcome foreign scientist and mining expert, the Spanish crown had established fertile ground for Humboldt's investigations into mining.

Spanish America's ancient civilizations were a source of interest for Humboldt, who included images of Mexican manuscripts (or codices) and Inca ruins in his richly illustrated Vues des cordillères et monuments des peuples indigènes de l'Amerique (1810–1813), the most experimental of Humboldt's publications, since it does not have "a single ordering principle" but his opinions and contentions based on observation.[79] For Humboldt, a key question was the influence of climate on the development of these civilizations.[80] When he published his Vues des cordillères, he included a color image of the Aztec calendar stone, which had been discovered buried in the main plaza of Mexico City in 1790, along with select drawings of the Dresden codex and others he sought out later in European collections. His aim was to muster evidence that these pictorial and sculptural images could allow the reconstruction of prehispanic history. He sought out Mexican experts in the interpretation of sources from there, especially Antonio Pichardo, who was the literary executor of Antonio de León y Gama's work. For American-born Spaniards (creoles) who were seeking sources of pride in Mexico's ancient past, Humboldt's recognition of these ancient works and dissemination in his publications was a boon. He read the work of exiled Jesuit Francisco Javier Clavijero, which celebrated Mexico's prehispanic civilization, and which Humboldt invoked to counter the pejorative assertions about the new world by Buffon, de Pauw, and Raynal.[81] Humboldt ultimately viewed both the prehispanic realms of Mexico and Peru as despotic and barbaric.[82] However, he also drew attention to indigenous monuments and artifacts as cultural productions that had "both ... historical and artistic significance".[83]

One of his most widely read publications resulting from his travels and investigations in Spanish America was the Essai politique sur le royaum de la Nouvelle Espagne, quickly translated to English as Political Essay on the Kingdom of New Spain (1811).[84] This treatise was the result of Humboldt's own investigations as well as the generosity of Spanish colonial officials for statistical data.[85]

1804 Map of the Louisiana Territory. Jefferson and his cabinet sought information from Humboldt when he visited Washington, D.C., about Spain's territory in Mexico, now bordering the U.S.

Leaving from Cuba, Humboldt decided to take an unplanned short visit to the United States. Knowing that the current U.S. president, Thomas Jefferson, was himself a scientist, Humboldt wrote to him saying that he would be in the United States. Jefferson warmly replied, inviting him to visit the White House in the nation's new capital. In his letter Humboldt had gained Jefferson's interest by mentioning that he had discovered mammoth teeth near the Equator. Jefferson had previously written that he believed mammoths had never lived so far south. Humboldt had also hinted at his knowledge of New Spain.[86]

Arriving in Philadelphia, which was a center of learning in the U.S., Humboldt met with some of the major scientific figures of the era, including chemist and anatomist Caspar Wistar, who pushed for compulsory smallpox vaccination, and botanist Benjamin Smith Barton, as well as physician Benjamin Rush, a signer of the Declaration of Independence, who wished to hear about cinchona bark from a South American tree, which cured fevers.[87] Humboldt later published a treatise in English on cinchona.[88]

After arriving in Washington D.C, Humboldt held numerous intense discussions with Jefferson on both scientific matters and also his year-long stay in New Spain. Jefferson had only recently concluded the Louisiana Purchase, which now placed New Spain on the southwest border of the United States. The Spanish minister in Washington, D.C. had declined to furnish the U.S. government with information about Spanish territories, and access to the territories was strictly controlled. Humboldt was able to supply Jefferson with the latest information on the population, trade agriculture and military of New Spain. This information would later be the basis for his Essay on the Political Kingdom of New Spain (1810).

Jefferson was unsure of where the border of the newly-purchased Louisiana was precisely, and Humboldt wrote him a two-page report on the matter. Jefferson would later refer to Humboldt as "the most scientific man of the age". Albert Gallatin, Secretary of the Treasury, said of Humboldt "I was delighted and swallowed more information of various kinds in less than two hours than I had for two years past in all I had read or heard." Gallatin, in turn, supplied Humboldt with information he sought on the United States.[86]

After six weeks, Humboldt set sail for Europe from the mouth of the Delaware and landed at Bordeaux on 3 August 1804.

Humboldt kept a detailed diary of his sojourn to Spanish America, running some 4,000 pages, which he drew on directly for his multiple publications following the expedition. The leather-bound diaries themselves are now in Germany, having been returned from Russia to East Germany, where they were taken by the Red Army after World War II. Following German reunification, the diaries were returned to a descendant of Humboldt. For a time, there was concern about their being sold, but that was averted.[89] A government-funded project to digitize the Spanish American expedition as well as his later Russian expedition has been undertaken (2014–2017) by the University of Potsdam and the German State Library—Prussian Cultural Heritage Foundation.[90]

Humboldt's decades' long endeavor to publish the results of this expedition not only resulted in multiple volumes, but also made his international reputation in scientific circles. Humboldt came to be well-known with the reading public as well, with popular, densely illustrated, condensed versions of his work in multiple languages. Bonpland, his fellow scientist and collaborator on the expedition, collected botanical specimens and preserved them, but unlike Humboldt who had a passion to publish, Bonpland had to be prodded to do the formal descriptions. Many scientific travelers and explorers produced huge visual records, which remained unseen by the general public until the late nineteenth century, in the case of the Malaspina Expedition, and even the late twentieth century, when Mutis's botanical, some 12,000 drawings from New Granada, was published. Humboldt, by contrast, published immediately and continuously, using and ultimately exhausting his personal fortune, to produce both scientific and popular texts. Humboldt's name and fame were made by his travels to Spanish America, particularly his publication of the Political Essay on the Kingdom of New Spain. His image as the premier European scientist was a later development.[91]

For the Bourbon crown, which had authorized the expedition, the returns were not only tremendous in terms of sheer volume of data on their New World realms, but in dispelling the vague and pejorative assessments of the New World by Guillaume-Thomas Raynal, Georges-Louis Leclerc, Comte de Buffon, and William Robertson. The achievements of the Bourbon regime, especially in New Spain, were evident in the precise data Humboldt systematized and published.[71]

This memorable expedition may be regarded as having laid the foundation of the sciences of physical geography, plant geography, and meteorology. Key to that was Humboldt's meticulous and systematic measurement of phenomena with the most advanced instruments then available. He closely observed plant and animal species in situ, not just in isolation, noting all elements in relation to one other. He collected specimens of plants and animals, dividing the growing collection so that if a portion was lost, other parts might survive.

Humboldt depicted by American artist Charles Willson Peale, 1805, who met Humboldt when he visited the U.S. in 1804

Humboldt saw the need for an approach to science that could account for the harmony of nature among the diversity of the physical world. For Humboldt, "the unity of nature" meant that it was the interrelation of all physical sciences—such as the conjoining between biology, meteorology and geology—that determined where specific plants grew. He found these relationships by unraveling myriad, painstakingly collected data,[92] data extensive enough that it became an enduring foundation upon which others could base their work. Humboldt viewed nature holistically, and tried to explain natural phenomena without the appeal to religious dogma. He believed in the central importance of observation, and as a consequence had amassed a vast array of the most sophisticated scientific instruments then available. Each had its own velvet lined box and was the most accurate and portable of its time; nothing quantifiable escaped measurement. According to Humboldt, everything should be measured with the finest and most modern instruments and sophisticated techniques available, for that collected data was the basis of all scientific understanding.

This quantitative methodology would become known as Humboldtian science. Humboldt wrote "Nature herself is sublimely eloquent. The stars as they sparkle in firmament fill us with delight and ecstasy, and yet they all move in orbit marked out with mathematical precision."[93]

Humboldt's Naturgemälde, also known as the Chimborazo Map, is his depiction of the volcanoes Chimborazo and Cotopaxi in cross section, with detailed information about plant geography. The illustration was published in The Geography of Plants, 1807, in a large format (54 cm x 84 cm). Largely used for global warming analyses, this map depicts in fact the vegetation of another volcano: the Antisana.[94]

His Essay on the Geography of Plants (published first in French and then German, both in 1807) was based on the then novel idea of studying the distribution of organic life as affected by varying physical conditions.[18] This was most famously depicted in his published cross-section of Chimborazo, approximately two feet by three feet (54 cm x 84 cm) color pictorial, he called Ein Naturgemälde der Anden and what is also called the Chimborazo Map. It was a fold-out at the back of the publication.[95] Humboldt first sketched the map when he was in South America, which included written descriptions on either side of the cross-section of Chimborazo. These detailed the information on temperature, altitude, humidity, atmosphere pressure, and the animal and plants (with their scientific names) found at each elevation. Plants from the same genus appear at different elevations. The depiction is on an east-west axis going from the Pacific coast lowlands to the Andean range of which Chimborazo was a part, and the eastern Amazonian basin. Humboldt showed the three zones of coast, mountains, and Amazonia, based on his own observations, but he also drew on existing Spanish sources, particularly Pedro Cieza de León, which he explicitly referred to. The Spanish American scientist Francisco José de Caldas had also measured and observed mountain environments and had earlier come to similar ideas about environmental factors in the distribution of life forms.[96] Humboldt was thus not putting forward something entirely new, but it is argued that his finding is not derivative either.[97] The Chimborazo map displayed complex information in an accessible fashion. The map was the basis for comparison with other major peaks. "The Naturgemälde showed for the first time that nature was a global force with corresponding climate zones across continents."[98] Another assessment of the map is that it "marked the beginning of a new era of environmental science, not only of mountain ecology but also of global-scale biogeophysical patterns and processes."[99]

Isothermal map of the world using Humboldt's data by William Channing Woodbridge

By his delineation (in 1817) of isothermal lines, he at once suggested the idea and devised the means of comparing the climatic conditions of various countries. He first investigated the rate of decrease in mean temperature with the increase in elevation above sea level, and afforded, by his inquiries regarding the origin of tropical storms, the earliest clue to the detection of the more complicated law governing atmospheric disturbances in higher latitudes.[18][100] This was a major contribution to climatology.[101][102]

His discovery of the decrease in intensity of Earth's magnetic field from the poles to the equator was communicated to the Paris Institute in a memoir read by him on 7 December 1804. Its importance was attested by the speedy emergence of rival claims.[18]

His services to geology were based on his attentive study of the volcanoes of the Andes and Mexico, which he observed and sketched, climbed, and measured with a variety of instruments. By climbing Chimborazo, he established an altitude record which became the basis for measurement of other volcanoes in the Andes and the Himalayas. As with other aspects of his investigations, he developed methods to show his synthesized results visually, using the graphic method of geologic-cross sections.[103] He showed that volcanoes fell naturally into linear groups, presumably corresponding with vast subterranean fissures; and by his demonstration of the igneous origin of rocks previously held to be of aqueous formation, he contributed largely to the elimination of erroneous views, such as Neptunism.[18]

Humboldt was a significant contributor to cartography, creating maps, particularly of New Spain, that became the template for later mapmakers in Mexico. His careful recording of latitude and longitude led to accurate maps of Mexico, the port of Acapulco, the port of Veracruz, and the Valley of Mexico, and a map showing trade patterns among continents. His maps also included schematic information on geography, converting areas of administrative districts (intendancies) using proportional squares.[104] The U.S. was keen to see his maps and statistics on New Spain, since they had implication for territorial claims following the Louisiana Purchase.[105] Later in life, Humboldt published three volumes (1836–39) examining sources that dealt with the early voyages to the Americas, pursuing his interest in nautical astronomy in the fifteenth and sixteenth centuries. His research yielded the origin of the name "America", put on a map of the Americas by Martin Waldseemüller.[106]

Humboldt's depiction of an Andean condor, an example of his detailed drawing

Humboldt conducted a census of the indigenous and European inhabitants in New Spain, publishing a schematized drawing of racial types and populations distribution, grouping them by region and social characteristics.[107] He estimated the population to be six million individuals.[108][109] He estimated Indians to be forty percent of New Spain's population, but their distribution being uneven; the most dense were in the center and south of Mexico, the least dense in the north. He presented these data in chart form, for easier understanding.[110] He also surveyed the non-Indian population, categorized as Whites (Spaniards), Negroes, and castes (castas).[111] American-born Spaniards, so-called creoles had been painting depictions of mixed-race family groupings in the eighteenth century, showing father of one racial category, mother of another, and the offspring in a third category in hierarchical order, so racial hierarchy was an essential way elites viewed Mexican society.[112] Humboldt reported that American-born Spaniards were legally racial equals of those born in Spain, but the crown policy since the Bourbons took the Spanish throne privileged those born in Iberia. Humboldt observed that "the most miserable European, without education and without intellectual cultivation, thinks himself superior to whites born in the new continent".[113] The truth in this assertion, and the conclusions derived from them, have been often disputed as superficial, or politically motivated, by some authors, considering that between 40% and 60% of high offices in the new world were held by creoles.[114][115] The enmity between some creoles and the peninsular-born whites increasingly became an issue in the late period of Spanish rule, with creoles increasingly alienated from the crown. Humboldt's assessment was that royal government abuses and the example of a new model of rule in the United States were eroding the unity of whites in New Spain.[116] Humboldt's writings on race in New Spain were shaped by the memorials of the classical liberal, enlightened Bishop-elect of Michoacán, Manuel Abad y Queipo, who personally presented Humboldt with his printed memorials to the Spanish crown critiquing social and economic conditions and his recommendations for eliminating them.[117][115]

One scholar says that his writings contain fantastical descriptions of America, while leaving out its inhabitants, stating that Humboldt, coming from the Romantic school of thought, believed '... nature is perfect till man deforms it with care'.[118] The further assessment is that he largely neglected the human societies amidst nature. Views of indigenous peoples as 'savage' or 'unimportant' leaves them out of the historical picture.[118] Other scholars counter that Humboldt dedicated large parts of his work to describing the conditions of slaves, indigenous peoples, mixed-race castas, and society in general. He often showed his disgust for the slavery[119] and inhumane conditions in which indigenous peoples and others were treated and he often criticized Spanish colonial policies.[120]

Humboldt was not primarily an artist, but he could draw well, allowing him to record a visual record of particular places and their natural environment. Many of his drawings became the basis for illustrations of his many scientific and general publications. Artists whom Humboldt influenced, such as Johann Moritz Rugendas, followed in his path and painted the same places Humboldt had visited and recorded, such as the basalt formations in Mexico, which was an illustration in his Vues des Cordillères.[121][122]

The editing and publication of the encyclopedic mass of scientific, political and archaeological material that had been collected by him during his absence from Europe was now Humboldt's most urgent desire. After a short trip to Italy with Joseph Louis Gay-Lussac for the purpose of investigating the law of magnetic declination and a stay of two and a half years in Berlin, in the spring of 1808, he settled in Paris. His purpose for being located there was to secure the scientific cooperation required for bringing his great work through the press. This colossal task, which he at first hoped would occupy but two years, eventually cost him twenty-one, and even then it remained incomplete.

• 
  House where Humboldt and Bonpland lived in Mexico City in 1803, located at 80 Rep. de Uruguay in the historic centre, just south of the Zocalo
• 
  Statue to Humboldt in Alameda Park, Mexico City, erected 1999 on the two hundredth-anniversary of the beginning of his travels to Spanish America
• 
  Statue of Humboldt in Cuernavaca, Mexico
• 
  Waterfall over the Basaltic Prisms of Santa María Regla, Huasca de Ocampo, Hidalgo, Mexico, that Humboldt sketched

Photograph of Humboldt in his later years

Kosmos was Humboldt's multi-volume effort in his later years to write a work bringing together all the research from his long career. The writing took shape in lectures he delivered before the University of Berlin in the winter of 1827–28. These lectures would form "the cartoon for the great fresco of the [K]osmos".[151] His 1829 expedition to Russia supplied him with data comparative to his Latin American expedition.[152]

The first two volumes of the Kosmos were published between the years 1845 and 1847 were intended to comprise the entire work, but Humboldt published three more volumes, one of which was posthumous. Humboldt had long aimed to write a comprehensive work about geography and the natural sciences. The work attempted to unify the sciences then known in a Kantian framework. With inspiration from German Romanticism, Humboldt sought to create a compendium of the world's environment.[11] He spent the last decade of his long life—as he called them, his "improbable" years—continuing this work. The third and fourth volumes were published in 1850–58; a fragment of a fifth appeared posthumously in 1862.

His reputation had long since been made with his publications on the Latin American expedition. There is not a consensus on the importance of Kosmos. One scholar, who stresses the importance of Humboldt's Political Essay on the Kingdom of New Spain as essential reading, dismisses Kosmos as "little more than an academic curiosity".[153] A different opinion is that Kosmos was his "most influential book".[152]

As with most of Humboldt's works, Kosmos was also translated into multiple languages in editions of uneven quality. It was very popular in Britain and America. In 1849 a German newspaper commented that in England two of the three different translations were made by women, "while in Germany most of the men do not understand it".[154] The first translation by Augustin Pritchard—published anonymously by Mr. Baillière (volume I in 1845 and volume II in 1848)—suffered from being hurriedly made. In a letter Humboldt said of it: "It will damage my reputation. All the charm of my description is destroyed by an English sounding like Sanskrit."

The other two translations were made by Elizabeth Juliana Leeves Sabine under the superintendence of her husband Col. Edward Sabine (4 volumes 1846–1858), and by Elise Otté (5 volumes 1849–1858, the only complete translation of the 4 German volumes). These three translations were also published in the United States. The numbering of the volumes differs between the German and the English editions. Volume 3 of the German edition corresponds to the volumes 3 and 4 of the English translation, as the German volume appeared in 2 parts in 1850 and 1851. Volume 5 of the German edition was not translated until 1981, again by a woman.[155] Otté's translation benefited from a detailed table of contents, and an index for every volume; of the German edition only volumes 4 and 5 had (extremely short) tables of contents, and the index to the whole work only appeared with volume 5 in 1862. Less well known in Germany is the atlas belonging to the German edition of the Cosmos "Berghaus' Physikalischer Atlas", better known as the pirated version by Traugott Bromme under the title "Atlas zu Alexander von Humboldt's Kosmos" (Stuttgart 1861).

In Britain, Heinrich Berghaus planned to publish together with Alexander Keith Johnston a "Physical Atlas". But later Johnston published it alone under the title "The Physical Atlas of Natural Phenomena". In Britain its connection to the Cosmos seems not have been recognized.[156]

Muisca numerals as noted by Humboldt

Alexander von Humboldt published prolifically throughout his life. Many works were published originally in French or German, then translated to other languages, sometimes with competing translation editions. Humboldt himself did not keep track of all the various editions.[157] He wrote specialized works on particular topics of botany, zoology, astronomy, mineralogy, among others, but he also wrote general works that attracted a wide readership, especially his Personal Narrative of Travels to the Equinoctial Regions of the New Continent during the years 1799–1804[158] His Political Essay on the Kingdom of New Spain was widely read in Mexico itself, the United States, as well as in Europe.[159]

Many of the original works have been digitally scanned by the Biodiversity Library.[160] There have been new editions of print works, including his Views of the Cordilleras and Monuments of the Indigenous Peoples of the Americas (2014), which includes reproductions of all the color and black and white plates. In the original edition, the publication was in a large format and quite expensive.[161] There is a 2009 translation of his Geography of Plants[162] and a 2014 English edition of Views of Nature.[163]

• 
  Ferdinand Bellermann, Rooster Salesman
• 
  Ferdinand Bellermann, Colonia Tovar
• 
  Ferdinand Bellermann, Sugar Plantation near Puerto Cabello
• 
  Ferdinand Bellermann. Llaneros (1843). Venezuela.[185]
• 
  Eduard Hildebrandt, Passage with Indians (Brazil)
• 
  Frederic Edwin Church, Cotopaxi, (1855)
• 
  Frederic Edwin Church, Cotopaxi, 1855
• 
  Frederic Edwin Church, Cotopaxi (1862) (in eruption)

Humboldt's seal on a private letter

In the Napoleonic wars, Prussia had capitulated to France, signing the Treaty of Tilsit. The Prussian royal family returned to Berlin, but sought better terms of the treaty and Friedrich Wilhelm III commissioned his younger brother Prince Wilhelm with this. Friedrich Wilhelm III asked Alexander to be part of the mission, charged with introducing the prince to Paris society. This turn of events for Humboldt could not have been better, since he desired to live in Paris rather than Berlin.[186]

In 1814 Humboldt accompanied the allied sovereigns to London. Three years later he was summoned by the king of Prussia to attend him at the congress of Aachen. Again in the autumn of 1822 he accompanied the same monarch to the Congress of Verona, proceeded thence with the royal party to Rome and Naples and returned to Paris in the spring of 1823. Humboldt had long regarded Paris as his true home. Thus, when at last he received from his sovereign a summons to join his court at Berlin, he obeyed reluctantly.

Between 1830 and 1848 Humboldt was frequently employed in diplomatic missions to the court of King Louis Philippe of France, with whom he always maintained the most cordial personal relations. Charles X of France had been overthrown, with Louis-Philippe of the house of Orléans becoming king. Humboldt knew the family, and he was sent by the Prussian monarch to Paris to report on events to his monarch. He spent three years in France, from 1830 to 1833. His friends François Arago and François Guizot, were appointed to posts in Louis-Philippe's government.[187]

Humboldt's brother, Wilhelm, died on 8 April 1835. Alexander lamented that he had lost half of himself with the death of his brother. Upon the accession of the crown prince Frederick William IV in June 1840, Humboldt's favor at court increased. Indeed, the new king's craving for Humboldt's company became at times so importunate as to leave him only a few waking hours to work on his writing.

Portrait of Humboldt by Julius Schrader, 1859. Metropolitan Museum of Art

Because Humboldt did not mention God in his work Cosmos, and sometimes spoke unfavourably of religious attitudes, it was occasionally speculated that he was a materialist philosopher, or perhaps an atheist.[188] However, unlike irreligious figures such as Robert G. Ingersoll, who went so far as to use Humboldtian science to campaign against religion,[189] Humboldt himself denied imputations of atheism. In a letter to Varnhagen von Ense he emphasized that he believed the world had indeed been created, writing of Cosmos: "...'creation' and the 'created world' are never lost sight of in the book. And did I not, only eight months ago, in the French translation, say, in the plainest terms: 'It is this necessity of things, this occult but permanent connection, this periodical return in the progress, development of formation, phenomena, and events which constitute 'Nature' submissive to a controlling power?'"[190]

It has been argued that "although Humboldt emphasizes the basis of morality in the nature of man, he does acknowledge that a belief in God is linked directly to acts of virtue" and therefore "the dignity of man lies at the centre of Humboldt's religious thought".[191]

Humboldt also believed firmly in an afterlife.[192] A letter he wrote to his friend Charlotte Hildebrand Diede states: "God constantly appoints the course of nature and of circumstances; so that, including his existence in an eternal future, the happiness of the individual does not perish, but on the contrary grows and increases."[193]

Humboldt remained distant of organized religion: he did not believe in the Bible as an inerrant document, nor in the divinity of Jesus; yet, Humboldt still held deep respect for the ideal side of religious belief and church life within human communities.[194] He differentiated between "negative" religions, and those "all positive religions [which] consist of three distinct parts—a code of morals which is nearly the same in all of them, and generally very pure; a geological chimera, and a myth or a little historical novel".[195] In Cosmos, he wrote about how rich geological descriptions were found in different religious traditions, and stated: "Christianity gradually diffused itself, and, wherever it was adopted as the religion of the state, it not only exercised a beneficial condition on the lower classes by inculcating the social freedom of mankind, but also expanded the views of men in their communion with Nature...this tendency to glorify the Deity in his works gave rise to a taste for natural observation."[196]

Humboldt showed religious tolerance towards Judaism, and he criticized the political Jews Bill, which was an initiative intended to establish legal discrimination against Jews. He called this an "abominable" law, since he hoped to see Jews being treated equally in society.[197]

Alexander von Humboldt in his library in his Oranienburger Strasse, Berlin apartment, by Eduard Hildebrandt

Much of Humboldt's private life remains a mystery because he destroyed his private letters. While a gregarious personality, he may have harbored a sense of social alienation, which drove his passion for escape through travel.[198]

Humboldt never married: while he was charmed by a number of attractive women, including Henriette, the wife of his mentor Marcus Herz, his sister-in-law Caroline von Humboldt stated "nothing will ever have a great influence on Alexander that doesn't come through men".[199] He had many strong male friendships, and at times had romances with men.[200]

As a student he became infatuated with Wilhelm Gabriel Wegener, a theology student, penning a succession of letters expressing his "fervent love".[201] At 25 he met Reinhardt von Haeften (19 May 1772 – 20 October 1803), a 21-year-old lieutenant, with whom he lived and travelled for two years, and to whom he wrote in 1794: "I only live through you, my good precious Reinhardt". When von Haeften became engaged, Humboldt begged to remain living with him and his wife: "Even if you must refuse me, treat me coldly with disdain, I should still want to be with you... the love I have for you is not just friendship or brotherly love, it is veneration".[202]

A traveling companion in the Americas for five years was Aimé Bonpland, and in Quito in 1802 he met the Ecuadorian aristocrat Don Carlos Montúfar, who traveled with Humboldt to Europe and lived with him. In France, Humboldt traveled and lived with the physicist and balloonist Joseph Louis Gay Lussac. Later he had a deep friendship with the married French astronomer François Arago, whom he met daily for 15 years.[203]

Humboldt once wrote "I don't know sensual needs".[199] However, a pious travelling companion, Francisco José de Caldas, accused him of frequenting houses in Quito where "impure love reigned", of making friends with "obscene dissolute youths", of giving vent to "shameful passions of his heart", and dropping him to travel with "Bonpland and his Adonis"[Monúfar].[204]

Humboldt inherited a significant fortune, but the expense of his travels, and most especially of publishing (thirty volumes in all), had by 1834 made him totally reliant on the pension of King Frederick William III.[205] Although he preferred living in Paris, by 1836 the King had insisted he return to Germany. He lived with the Court at Sanssouci, and latterly in Berlin, with his valet Seifert, who had accompanied him to Russia in 1829.[206]

Signature of Humboldt late in life, when his handwriting became increasingly difficult to read

Four years before his death, Humboldt executed a deed of gift transferring his entire estate to Seifert,[207][208] who had by then married and set up a household near Humboldt's apartment. Humboldt had become godfather to his daughter.[209] The scale of the bequest has always drawn speculation, especially as Seifert was some thirty years younger, and introducing lower class partners into households under the guise of servants was then a common practice.[210]

In 1908, the sexual researcher Paul Näcke gathered reminiscences from homosexuals[211] including Humboldt's friend the botanist Carl Bolle, then nearly 90 years old: some of the material was incorporated by Magnus Hirschfeld into his 1914 study Homosexuality in Men and Women.[212] However, speculations about Humboldt's private life and possible homosexuality continue to remain a fractious issue amongst scholars, particularly as earlier biographers had portrayed him as "a largely asexual, Christ-like Humboldt figure...suitable as a national idol".[213]

On 24 February 1857, Humboldt suffered a minor stroke, which passed without perceptible symptoms.[214] It was not until the winter of 1858–1859 that his strength began to decline; on 6 May 1859, he died peacefully in Berlin, aged 89. His last words were reported to be "How glorious these sunbeams are! They seem to call Earth to the Heavens!"[215] His remains were conveyed in state through the streets of Berlin, in a hearse drawn by six horses. Royal chamberlains led the cortège, each charged with carrying a pillow with Humboldt's medals and other decorations of honor. Humboldt's extended family, descendants of his brother Wilhelm, walked in the procession. Humboldt's coffin was received by the prince-regent at the door of the cathedral. He was interred at the family resting-place at Tegel, alongside his brother Wilhelm and sister-in-law Caroline.[216]

• 1842: Pour le Mérite (civil division)[217]
• 1850: Knight Grand Cross of the Order of Saints Maurice and Lazarus[218]
• 1863: Knight Grand Cross of the Order of Guadalupe

Humboldt described many geographical features and species that were hitherto unknown to Europeans. Species named after him include:

• Spheniscus humboldti—Humboldt penguin
• Dosidicus gigas—Humboldt squid
• Lilium humboldtii—Humboldt's lily
• Phragmipedium humboldtii—an orchid
• Quercus humboldtii—South American (Andean) oak
• Conepatus humboldtii—Humboldt's hog-nosed skunk
• Annona humboldtii—Neotropical fruit tree or shrub
• Utricularia humboldtii—a bladderwort
• Geranium humboldtii—a cranesbill
• Salix humboldtiana—a South-American willow[219]
• Inia geoffrensis humboldtiana—Amazon river dolphin subspecies of Orinoco River basin
• Rhinocoryne humboldti—marine snail
• Bathybembix humboldti—marine snail
• Rhinella humboldti—Rivero's toad
• Pteroglossus humboldti—Humboldt's Araçari
• Hylocharis humboldtii—Humboldts humming bird
• Casignethus humboldti— beetle
• Elzunia humboldt— butterfly

• 
  Humboldt penguin, native to Chile and Peru
• 
  Humboldt squid found in the Humboldt Current
• 
  Quercus humboldtii, an Andean oak

Features named after him include:[220]

• 
  Humboldt Current
• 
  Pico Humboldt, Venezuela

The following places are named for Humboldt:[222]

• Mare Humboldtianum (lunar mare)
• 54 Alexandra (asteroid)
• 4877 Humboldt (asteroid)

• Humboldt University of Berlin is named after Alexander and his brother Wilhelm who founded it[223]
• Alexander von Humboldt Biological Resources Research Institute in Bogotá and Villa de Leiva, Colombia
• Humboldt State University in Arcata, California
• Universidad Alejandro de Humboldt in Caracas, Venezuela

• Alexander-von-Humboldt-Gymnasium, Konstanz, Germany
• Alexander von Humboldt German International School Montreal, Montreal, Canada
• Colegio Alemán Alexander von Humboldt, Mexico City, Mexico
• Deutsche Schule Lima Alexander von Humboldt, Lima, Peru
• Colegio Humboldt, Caracas, Venezuela

Alexander von Humboldt also lends his name to a prominent lecture series in Human geography in the Netherlands (hosted by the Radboud University Nijmegen). It is the Dutch equivalent of the widely known annual Hettner lectures at the University of Heidelberg.

After his death, Humboldt's friends and colleagues created the Alexander von Humboldt Foundation (Stiftung in German) to continue his generous support of young academics. Although the original endowment was lost in the German hyperinflation of the 1920s, and again as a result of World War II, the Foundation has been re-endowed by the German government to award young academics and distinguished senior academics from abroad. It plays an important role in attracting foreign researchers to work in Germany and enabling German researchers to work abroad for a period.

Edgar Allan Poe dedicated his last major work, Eureka: A Prose Poem, to Humboldt, "With Very Profound Respect". Humboldt's attempt to unify the sciences in his Kosmos was a major inspiration for Poe's project.

Alexander von Humboldt is also a German ship named after the scientist, originally built in 1906 by the German shipyard AG Weser at Bremen as Reserve Sonderburg. She was operated throughout the North and Baltic Seas until being retired in 1986. Subsequently, she was converted into a three-masted barque by the German shipyard Motorwerke Bremerhaven, and was re-launched in 1988 as Alexander von Humboldt.

The Jan De Nul Group operates a hopper dredger built in 1998 also named Alexander von Humboldt.[224]

Simón Bolívar wrote that "The real discoverer of South America was Humboldt, since his work was more useful for our people than the work of all conquerors".[225] Charles Darwin expressed his debt to Humboldt, and admiration for his work,[226] writing to Joseph Dalton Hooker that Humboldt was the "greatest scientific traveller who ever lived".[227] Wilhelm von Humboldt wrote that "Alexander is destined to combine ideas and follow chains of thoughts which would otherwise have remained unknown for ages. His depth, his sharp mind and his incredible speed are a rare combination." Johann Wolfgang Goethe observed that "Humboldt showers us with true treasures". Friedrich Schiller wrote that "Alexander impresses many, particularly when compared to his brother—because he shows off more!" José de la Luz y Caballero wrote that "Columbus gave Europe a New World; Humboldt made it known in its physical, material, intellectual, and moral aspects".

Napoléon Bonaparte remarked "You have been studying Botanics? Just like my wife!" Claude Louis Berthollet said "This man is as knowledgeable as a whole academy". Thomas Jefferson remarked "I consider him the most important scientist whom I have met". Emil du Bois-Reymond wrote that "Every assiduous scholar ... is Humboldt's son; we are all his family."[228] Robert G. Ingersoll wrote that "He was to science what Shakespeare was to the drama".[229]

Hermann von Helmholtz wrote that "During the first half of the present century we had an Alexander von Humboldt, who was able to scan the scientific knowledge of his time in its details, and to bring it within one vast generalization. At the present juncture, it is obviously very doubtful whether this task could be accomplished in a similar way, even by a mind with gifts so peculiarly suited for the purpose as Humboldt's was, and if all his time and work were devoted to the purpose."[230]

• 1829 Universität Dorpat

• Sculptures
• 
  A 1959 postage stamp from the Soviet Union
• 
  Bust of Humboldt at the University of Havana
• 
  Humboldt statue in Budapester Strasse, Berlin
• 
  Statue in Humboldt Park, Chicago
• 
  Statue of Humboldt in Allegheny West Park, Pittsburgh, Pennsylvania
• 
  Statue at Humboldt University of Berlin, describing him as "the second discoverer of Cuba"
• 
  Bust of Humboldt in Central Park, New York
• 
  Statue in Alameda Central, Mexico City.
• 
  Monument in El Ejido Park, Quito, Ecuador

• Letters of Alexander von Humboldt to Varnhagen von Ense. From 1827 to 1858. With extracts from Varnhagen's diaries, and letters of Varnhagen and others to Humboldt. Tr. from the 2d German by Friedrich Kapp (ed.), biodiversitylibrary.org
• Letters of Alexander von Humboldt written between the years 1827 and 1858 to Varnhagen von Ense together with extracts from Varnhagen's diaries, and letters of Varnhagen and others to Humboldt/ authorized translation from the German (with explanatory notes and a full index of names), biodiversitylibrary.org
• Nova genera et species plantarum (7 vols. folio, 1815–1825), contains descriptions of above 4500 species of plants collected by Humboldt and Bonpland, was mainly compiled by Carl Sigismund Kunth; J. Oltmanns assisted in preparing the Recueil d'observations astronomiques (1808); Cuvier, Latreille, Valenciennes and Gay-Lussac cooperated in the Recueil d'observations de zoologie et d'anatomie comparée (1805–1833).[18]

• Daniel Kehlmann's 2005 novel Die Vermessung der Welt, translated into English by Carol Brown Janeway as Measuring the World in 2006, explores Humboldt's life through the lens of historical fiction, contrasting his character and contributions to science with those of Carl Friedrich Gauss.

• Werner Herzog portrays Humboldt in Edgar Reitz's 2013 film Home from Home.
• Measuring the World is a 2012 German / Austrian 3D film directed by Detlev Buck and was released in 2012 based on the eponymous novel by Daniel Kehlmann.
• Climbing the Chimborazo (Ascenso al volcán Chimborazo) (1989), a film directed by Rainer Simon.

• The Alexander von Humboldt Foundation
• The Alexander von Humboldt Digital Library A virtual research environment on the works of Alexander von Humboldt. A project by the University of Applied Sciences Offenburg and the University of Kansas.
• avhumboldt.de Humboldt Informationen online A large collection of data, texts and visuals concerning Alexander von Humboldt in German, English, Spanish and French. A project by the Chair of Romance Literatures, University of Potsdam (Germany).
• Web site of the Humboldt Lecture series in Nijmegen, the Netherlands
• Alexander von Humboldt. Polymath Virtual Library, Fundación Ignacio Larramendi (in Spanish)
• Virtual exhibition on Paris Observatory digital library (in French)

• Works by Alexander von Humboldt at Biodiversity Heritage Library
• Works by Alexander von Humboldt at Project Gutenberg
• Works by Alexander von Humboldt at LibriVox (public domain audiobooks)
• Works by or about Alexander von Humboldt at Internet Archive

• "Alexander von Humboldt", from In Our Time, a 45 minute BBC Radio 4 program.
• Alexander von Humboldt featured on the East German 5 Marks banknote from 1964
• A. J. P. Raat, "Alexander von Humboldt and Coenraad Jacob Temminck", Zoologische Bijdragen, Vol. 21, 1976, p. 19–38
• Bois-Reymond, Emil du (December 1883). "Alexander von Humboldt" . Popular Science Monthly. Vol. 24. pp. 145–160.
• "Humboldt, Friedrich Heinrich Alexander von" . Appletons' Cyclopædia of American Biography. 1900.
• L. Kellner, "Alexander Von Humboldt and the history of international scientific collaboration", Scientia: rivista internazionale di sintesi scientifica, 95, 1960, pp. 252–256