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Updated: May 5, 2025
The determination of the heights of mountains by triangulation is, of course, the method that in general commends itself to the topographer, though it may be questioned whether the very general use of aneroids for barometric determinations has not thrown this latter means of measuring altitudes into undeserved discredit when the mercurial barometer is used instead of its convenient but unreliable substitute.
I have previously had several severe attacks of snow-blindness. We had two photographic cameras, an air thermometer, two aneroids with altitude scale to 15,000 feet, and two hypsometers. The hypsometer is only an instrument for determining the boiling-point, which gives one the height above the sea. The method is both simple and reliable.
The watches and chronometer were looked upon with suspicion, their ticking causing curiosity and even anxiety. They were passed round, and mercilessly thrown about from one person to the other until they stopped ticking. They were then pronounced "dead." The compasses and aneroids, which they could not distinguish from watches, were soon thrown aside, as "they had no life in them."
We took what comfort we could from the fact that the aneroids, which had checked each other perfectly up to 17,000 feet, were now so obviously untrustworthy. We could only hope that both might prove to be inaccurate, as actually happened, and that both might now be reading too low. Anyhow, the north peak did look lower than we were.
Coxwell's assistant, seated on the ring above the car, began to take in light cargo in the shape of aneroids, barometers, bottles of brandy and water, and other useful articles. M. Duruof scrambled into the car, one of the men who had been weighing it down getting out to make room for him.
I set up and read the mercurial barometer, and when corrected for its own temperature it stood at 15.061. The boiling-point thermometer registered 180.5, as the point at which water boiled, with an air temperature of 35°. It took one hour to boil the rice for supper. The aneroids stood at 14.8 and 14.9, still steadily losing on the mercurial barometer.
We pegged along until about half-past two, when the rapidly melting snow stopped all progress. At an altitude of about 18,450 feet, the Tucker tent was pitched on a fairly level snow field. We now noticed with dismay that the two big aneroids had begun to differ. As the sun declined the temperature fell rapidly.
It was not until we opened our specially ordered "mountain grub" boxes here in Chuquibamba that we found, alongside of the pemmican and self-heating tins of stew which had been packed for us in London by Grace Brothers, the two precious aneroids, each as large as a big alarm clock.
Although I used these aneroids principally for differential heights along my route, as aneroids cannot always be relied upon for great accuracy, I found on checking these particular instruments with the boiling-point thermometers that they were always extremely accurate.
The aneroids had kept fairly well with the mercurial barometer and the boiling-point thermometer until we moved to the ridge; from this time they displayed a progressive discrepancy therewith that put them out of serious consideration, and one was as bad as the other. Eleven thousand feet seemed the limit of their good behavior.
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