Humboldt on Chimborazo

At the beginning of the nineteenth century, Chimborazo, a snow-covered volcano in what is now Ecuador, was widely believed to be the highest mountain in the world. It was not, as it turned out, but it is remarkable in a way that nobody at the time could have known. Because the Earth bulges at the equator, its summit is the point on the planet's surface farthest from the Earth's center, more than two kilometers farther out than the summit of Everest.

On 23 June 1802, the Prussian naturalist Alexander von Humboldt set out to climb it. With him were the French botanist Aimé Bonpland, who had been traveling with him since they left Europe, and Carlos Montúfar, a twenty-one-year-old from Quito who had joined them in that city. They carried barometers and thermometers rather than ropes, and by Humboldt's own account they were equipped for nothing of the kind: their boots were soon soaked through, and they had no gloves.

The local men who had carried their equipment refused to go beyond the snow line, convinced that the attempt was impossible, so the three continued alone along a narrow ridge of rock and ice. As the air thinned, the symptoms we now call altitude sickness set in. Humboldt suffered from dizziness and nausea, and blood ran from his nose; Bonpland and Montúfar fared little better. Humboldt nonetheless stopped at intervals to record the temperature and the air pressure, to collect rocks and plants, and to note which plants were still managing to grow at that height.

Shortly after one in the afternoon, the ridge ended at a ravine that, by Humboldt's estimate, was some 120 meters deep, and that nobody could have crossed without equipment they did not have. Fog was closing in. They took their final measurements and turned back. From his barometer readings, Humboldt calculated that they had reached 5,878 meters, higher, he believed, than anyone had ever climbed, although historians now doubt that they came anywhere near that figure. The summit, at roughly 6,270 meters, was not reached until 1880, when Edward Whymper climbed it with two Italian guides.

What Humboldt brought down from the mountain, however, mattered far more than any record. Over the following years he turned the observations he had gathered on Chimborazo and other Andean peaks into a single, extraordinary image, published in 1807 in his essay on the geography of plants. It shows the volcano in cross-section, with the names of plants written onto its slopes at the heights where they grow, from the tropical forest at its foot to the last lichens beneath the snow. Beside it, columns of figures record temperature, air pressure and other conditions at each altitude.

Had he reached the summit, Humboldt might have been remembered mainly as a mountaineer. Having failed to, he left behind something rarer: a picture showing, at a glance, that life on a mountain is arranged in belts according to height, an idea that would help to found the science of biogeography.