Tool Users: Barometer

Posted on: September 21, 2020


[This story originally appeared in Alpinist 71, which is now available on some newsstands and in our online store. Only a small fraction of our many long-form stories from the print edition are ever uploaded to Alpinist.com. Be sure to pick up Alpinist 71 for all the goodness!—Ed.]

Evangelista Torricelli experimenting in the Alps with a barometer, 1643. [Illustration] Ernest Board, WikimediaEvangelista Torricelli experimenting in the Alps with a barometer, 1643. [Illustration] Ernest Board, Wikimedia

On June 23, 1802, Alexander von Humboldt and his three companions balanced their way up the knife-edge ridge of Chimborazo (20,561'), then thought to be the highest mountain in the world. One side of the precipice was a loose jumble of friable rock. On the other side, a steep snow slope glistened like glass. Nauseated and cold, the party became enveloped in a thick mist. They paused at a point where they could stand two abreast and took out a barometer.

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After another hour of climbing, the party stopped at a massive crevasse. With stiff fingers, Humboldt set up the barometer once more and calculated their height at 19,284 feet (modern estimates place him considerably lower). Though he had failed to reach the summit, Humboldt reached a world altitude record that stood for nearly thirty years. As if climbing high peaks wasn't difficult enough for early European explorers, measuring heights became an equally important (and demanding) obsession.

The earliest known large-scale height measurements began in antiquity. Using similar right-angled triangles, the height of large objects such as pyramids and mountains (the shortest "side" of a triangle) could be estimated by comparing the length of their longest sides. By the sixteenth century, scholars used instruments such as the quadrant to determine the actual angles of triangles, making their calculations more refined. Measuring an object's exact altitude via triangulation remained difficult, however, since atmospheric refraction (bending of the light waves) makes mountains appear higher than they are.

Enter the barometer. "We live submerged at the bottom of an ocean of the element air," Italian physicist Evangelista Torricelli proclaimed. In 1643, building on the work of his mentor, Galileo Galilei, Torricelli invented the first mercury barometer. His student, Vincenzo Viviani, filled several four-foot glass tubes with mercury and inverted them onto mercury-filled dishes to create a vacuum. They then noticed the mercury level in the tubes lowering or rising: the mercury would fall when the pressure of the surrounding air decreased and the weather turned poor, and it rose when the pressure increased and the weather turned fair.

A few years later, the French scientist Blaise Pascal and his brother-in-law used similar barometers to prove that air pressure changes at altitude. Lugging barometric tubes atop the 1465-meter Puy de Dome, they saw the mercury level drop over three inches because of the decreased air pressure. The result "ravished us with admiration and astonishment," Pascal later wrote. They repeated the experiment no less than five times in different weather before Pascal wrote an account recommending their method for measuring heights.

A newfound tension emerged between measuring the mountain and climbing it. Delicate mercury barometers had to be at least three feet long; for transport, they were encased in brass and packaged in sturdy leather cases that could be carried over the shoulder. Barometers also required a tripod to hang the tube. On ascents, mountaineers needed to find a suitable spot to set up the tripod, hang the tube, adjust the instrument to let the mercury descend, record a measurement and then carefully pack it all away. Many barometers broke, and measurements were still capricious, as bubbles or vapor distorted the readings, and differing temperatures led to fluctuations in air pressure.

Early mountaineering narratives are awash with barometer fables and fiascos. In 1786 Michel Paccard hauled a barometer on the first ascent of Mont Blanc; a year later, Horace Benedict de Saussure and his group took not one but two of the instruments for reciprocal checks. At the top, Saussure lingered for four and a half hours, bemoaning that the time was much too short to complete his measurements. His barometer, affectionately (or despairingly) called "the old man," accompanied him on all other mountain expeditions as well. In the Andes, Humboldt claimed to have "climbed all mountains with the barometer." One historian later dubbed Humboldt's entire journey a "barometric measurement campaign."

Toward the end of the nineteenth century, after national surveys had established the elevations of mountain ranges, the barometer's importance for height measurements waned, while the use of household barometers for weather forecasting flourished. As mountaineering transitioned from science to sport, climbers mocked the instrument and ridiculed scientific aims of mountaineering excursions altogether. In his 1871 The Playground of Europe, British alpinist Leslie Stephen wrote about his ascent of the Swiss Rothorn: "As we had, unluckily, no barometer, I am unable to give the usual information as to the extent of our deviation from the correct altitude; but the Federal map fixes the height at 13,855 feet." Later, stretched out on a meadow in the shadow of the mountain, Stephen and his companions pondered the pleasures and pains of mountaineering while they drank wine and smoked pipes.

In an age when peaks have been mapped and measured, Stephen's musings point us to the larger questions that remain—unable to be answered by instruments old or new—of why we climb mountains.

A barometer. [Photo] Clark Linehan. Special thanks to Don McCasland, Program Director, Blue Hill Observatory Science CenterA barometer. [Photo] Clark Linehan. Special thanks to Don McCasland, Program Director, Blue Hill Observatory Science Center

[Schaumann is the author of a forthcoming book titled Peak Pursuits: The Emergence of Mountaineering in the Nineteenth Century. This story originally appeared in Alpinist 71, which is now available on some newsstands and in our online store. Only a small fraction of our many long-form stories from the print edition are ever uploaded to Alpinist.com. Be sure to pick up Alpinist 71 for all the goodness!—Ed.]

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