The 100 Most Influential Scientists of All Time (17 page)

(b. Sept. 14, 1769, Berlin, Ger.—d. May 6, 1859, Berlin)

G
erman naturalist and explorer Alexander von Humboldt was a major figure in the classical period of physical geography and biogeography—areas of science now included in the earth sciences and ecology. With his book
Kosmos
he made a valuable contribution to the popularization of science. The Humboldt Current off the west coast of South America was named after him.

The conviction had grown in Humboldt that his real aim in life was scientific exploration, and in 1797 he set himself to acquiring a thorough knowledge of the systems of geodetic, meteorological, and geomagnetic measurements. He obtained permission from the Spanish government to visit the Spanish colonies in Central and South America.
Completely shut off from the outside world, these colonies offered enormous possibilities to a scientific explorer. Humboldt's social standing assured him of access to official circles, and in the Spanish prime minister Mariano de Urquijo he found an enlightened man who supported his application to the king for a royal permit. In the summer of 1799 he set sail from Marseille accompanied by the French botanist Aimé Bonpland, whom he had met in Paris, then the liveliest scientific centre in Europe. The estate he had inherited at the death of his mother enabled Humboldt to finance the expedition entirely out of his own pocket. Humboldt and Bonpland spent five years, from 1799 to 1804, in Central and South America, covering more than 6,000 miles (9,650 kilometres) on foot, on horseback, and in canoes. It was a life of great physical exertion and serious deprivation.

Starting from Caracas, they travelled south through grasslands and scrublands until they reached the banks of the Apure, a tributary of the Orinoco River. They continued their journey on the river by canoe as far as the Orinoco. Following its course and that of the Casiquiare, they proved that the Casiquiare River formed a connection between the vast river systems of the Amazon and the Orinoco. For three months Humboldt and Bonpland moved through dense tropical forests, tormented by clouds of mosquitoes and stifled by the humid heat. Their provisions were soon destroyed by insects and rain; the lack of food finally drove them to subsist on ground-up wild cacao beans and river water.

After a short stay in Cuba, Humboldt and Bonpland returned to South America for an extensive exploration of the Andes. From Bogotá to Trujillo, Peru, they wandered over the Andean Highlands—following a route now traversed by the Pan-American Highway, in their time a series of steep, rocky, and often very narrow paths. They climbed
a number of peaks, including all the volcanoes in the surroundings of Quito, Ecuador; Humboldt's ascent of Chimborazo (20,702 feet [6,310 metres]) to a height of 19,286 feet (5,878 metres), but short of the summit, remained a world mountain-climbing record for nearly 30 years. All these achievements were carried out without the help of modern mountaineering equipment, without ropes, crampons, or oxygen supplies; hence, Humboldt and Bonpland suffered badly from mountain sickness. But Humboldt turned his discomfort to advantage: he became the first person to ascribe mountain sickness to lack of oxygen in the rarefied air of great heights. He also studied the oceanic current off the west coast of South America that was originally named after him but is now known as the Peru Current.

In the spring of 1803, the two travellers sailed from Guayaquil to Acapulco, Mex., where they spent the last year of their expedition in a close study of this most developed and highly civilized part of the Spanish colonies. After a short stay in the United States, where Humboldt was received by President Jefferson, they sailed for France. Humboldt and Bonpland returned with an immense amount of information. In addition to a vast collection of new plants, there were determinations of longitudes and latitudes, measurements of the components of the Earth's geomagnetic field, and daily observations of temperatures and barometric pressure, as well as statistical data on the social and economic conditions of Mexico.

The years from 1804 to 1827 Humboldt devoted to publication of the data accumulated on the South American expedition. With the exception of brief visits to Berlin, he lived in Paris during this important period of his life. There
he found not only collaborators among the French scientists—the greatest of his time—but engravers for his maps and illustrations and publishers for printing the 30 volumes into which the scientific results of the expedition were distilled. Of great importance were the meteorological data, with an emphasis on mean daily and nightly temperatures, and Humboldt's representation on weather maps of isotherms (lines connecting points with the same mean temperature) and isobars (lines connecting points with the same barometric pressure for a given time or period)—all of which helped lay the foundation for the science of comparative climatology.

Even more important were his pioneering studies on the relationship between a region's geography and its flora and fauna, and, above all, the conclusions he drew from his study of the Andean volcanoes concerning the role played by eruptive forces and metamorphosis in the history and ongoing development of the Earth's crust. Lastly, his
Political Essay on the Kingdom of New Spain
contained a wealth of material on the geography and geology of Mexico, including descriptions of its political, social, and economic conditions, and also extensive population statistics.

During his years in Paris, Humboldt had the ability to cultivate deep and long-lasting friendships with well-known scientists, such as the renowned physicist and astronomer François Arago, and to evoke respect and admiration from the common man, an ability that reflected his generosity, humanity, and vision of what science could do. He was, moreover, always willing and anxious to assist young scientists at the beginning of their careers. Such men as the German chemist Justus von Liebig and the Swiss-born zoologist Louis Agassiz owed to Humboldt the means to continue their studies and embark on an academic career. The best proof of his wide interests and
affectionate nature lies in his voluminous correspondence: about 8,000 letters remain.

In 1827 Humboldt had to return to Berlin, where the King impatiently demanded his presence at court. In 1829 Humboldt was given the opportunity to visit Russia and Siberia. On the initiative of the Russian minister of finance, Count Yegor Kankrin, he was invited to visit the gold and platinum mines in the Urals. This expedition, lasting only one summer, was very different from the South American journey; the members, Humboldt and two young scientists, were accompanied throughout by an official guard, since they were guests of the Tsar. Humboldt and his companions had to endure tiresome receptions at the imperial court and in the homes of provincial governors. They travelled in carriages as far as the Altai Mountains and the Chinese frontier. The resulting geographical, geological, and meteorological observations, especially those regarding the Central Asian regions, were of great importance to the Western world, for Central Asia was then to a large degree unknown territory.

Even before his visit to Russia, he had returned to an investigation of a phenomenon that had aroused his interest in South America: the sudden fluctuations of the Earth's geomagnetic field—the so-called magnetic storms. With the help of assistants, he carried out observations of the movement of a magnetometer in a quiet garden pavilion in Berlin; but it had been clear to him for a number of years that, to discover whether these magnetic storms were of terrestrial or extraterrestrial origin, it would be necessary to set up a worldwide net of magnetic observatories. The German mathematician Carl Friedrich Gauss
had already begun to organize simultaneous measurements of the magnetic field by several observatories in Germany, England, and Sweden.

In 1836 Humboldt, still interested in the problem, approached the Royal Society in London with the request that it establish an additional series of stations in the British possessions overseas. As a result, the British government provided the means for permanent observatories in Canada, South Africa, Australia, and New Zealand and equipped an Antarctic expedition. With the help of the mass of data produced by this international scientific collaboration, one of the first of its kind, the English geophysicist Sir Edward Sabine later succeeded in correlating the appearance of magnetic storms in the Earth's atmosphere with the periodically changing activity of sunspots, thus proving the extraterrestrial origin of the storms.

During the last 25 years of his life, Humboldt was chiefly occupied with writing
Kosmos
, one of the most ambitious scientific works ever published. Four volumes appeared during his lifetime. Written in a pleasant, literary style,
Kosmos
gives a generally comprehensible account of the structure of the universe as then known, at the same time communicating the scientist's excitement and aesthetic enjoyment at his discoveries. Humboldt had taken immense pains to discipline his inclination to discursiveness, which often gave his writing a certain lack of logical coherence. He was rewarded for his effort by the success of his book, which, within a few years, had been translated into nearly all European languages.

(b. Jan. 22, 1775, Lyon, France—d. June 10, 1836, Marseille)

F
rench physicist André-Marie Ampère founded and named the science of electrodynamics, now known as
electromagnetism. His name endures in everyday life in the ampere, the unit for measuring electric current.

Ampère, who was born into a prosperous bourgeois family during the height of the French Enlightenment, personified the scientific culture of his day. His father, Jean-Jacques Ampère, was a successful merchant, and also an admirer of the philosophy of Jean-Jacques Rousseau, whose theories of education, as outlined in his treatise
Émile
, were the basis of Ampère's education. Rousseau argued that young boys should avoid formal schooling and pursue instead an “education direct from nature.” Ampère's father actualized this ideal by allowing his son to educate himself within the walls of his well-stocked library. French Enlightenment masterpieces such as Georges-Louis Leclerc, comte de Buffon's
Histoire naturelle, générale et particulière
(begun in 1749) and Denis Diderot and Jean Le Rond d'Alembert's
Encyclopédie
(volumes added between 1751 and 1772) thus became Ampère's schoolmasters. In addition, he
used his access to the latest mathematical books to begin teaching himself advanced mathematics at age 12. His mother was a devout woman, so Ampère was also initiated into the Catholic faith along with Enlightenment science.

The French Revolution (1787–99) that erupted during his youth was also formative. Ampère's father was called into public service by the new revolutionary government, becoming a justice of the peace in a small town near Lyon. Yet when the Jacobin faction seized control of the Revolutionary government in 1792, Jean-Jacques Ampère resisted the new political tides, and he was guillotined on Nov. 24, 1793, as part of the Jacobin purges of the period.

While the French Revolution brought these personal traumas, it also created new institutions of science that ultimately became central to André-Marie Ampère's professional success. Ampère's maturation corresponded with the transition to the Napoleonic regime in France, and he found new opportunities for success within the technocratic structures favoured by the new French emperor.

In 1802 Ampère produced
Considérations sur la théorie mathématique de jeu
(“Considerations on the Mathematical Theory of Games”), a treatise on mathematical probability that he sent to the Paris Academy of Sciences in 1803. In the following years Ampère engaged in a diverse array of scientific inquiries—writing papers and engaging in topics ranging from mathematics and philosophy to chemistry and astronomy. Such breadth was customary among the leading scientific intellectuals of the day.

In 1820 Ampère's friend and eventual eulogist François Arago demonstrated before the members of the French Academy of Sciences the surprising discovery of Danish physicist Hans Christiaan Ørsted that a magnetic needle
is deflected by an adjacent electric current. Ampère was well prepared to throw himself fully into this new line of research.

Ampère immediately set to work developing a mathematical and physical theory to understand the relationship between electricity and magnetism. Extending Ørsted's experimental work, Ampère showed that two parallel wires carrying electric currents repel or attract each other, depending on whether the currents flow in the same or opposite directions, respectively. He also applied mathematics in generalizing physical laws from these experimental results. Most important was the principle that came to be called Ampère's law, which states that the mutual action of two lengths of current-carrying wire is proportional to their lengths and to the intensities of their currents. Ampère also applied this same principle to magnetism, showing the harmony between his law and French physicist Charles Augustin de Coulomb's law of magnetic action. Ampère's devotion to, and skill with, experimental techniques anchored his science within the emerging fields of experimental physics.