Courmayeur · Italy

Saussure on the Col du Géant

In July 1788 a Geneva scientist had a hut built upon this col, at 3,365 metres, and remained in it for seventeen days. Horace-Bénédict de Saussure had climbed Mont Blanc the summer before and had found that the summit taught him very little. What he required was time. He carried barometers, thermometers and hygrometers up here, with his son and a small team, and took readings twice a day: pressure, humidity, the temperature at which water boils, and the depth of the blue overhead, which he measured with an instrument of his own invention. He wished to know how the atmosphere actually behaved at altitude, rather than deduce it from the valley floor. The weather was poor almost throughout: cloud rose from the glacier and for whole days nothing could be distinguished. He returned home with more readings than had ever been taken at that height, and they were worth more than the summit.

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Why measure the blue of the sky?

To find out how much air was above him. The thinner and cleaner the atmosphere, the darker the sky. Saussure built a cyanometer, a strip of 53 shades of blue, and held the sky against it. It was an ingenious way to measure what nobody could yet weigh.

Had he climbed Mont Blanc?

Yes, in August 1787, a year after the first ascent by Jacques Balmat and Michel Paccard. Saussure had offered a reward for a route up it in 1760, and waited twenty-six years for someone to come and collect it.

What was it like up there?

Cold, and often shut in by storms. The hut was carried up in pieces and put together on the col, and guides came and went with food and firewood. His son Nicolas-Théodore was with him and kept a record of the days himself.

Where it is

Punta Helbronner, Colle del Gigante, 11013 Courmayeur · 45.84587, 6.93176 · Open in Maps

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