The height of K2 is put down as 28,250 feet above the sea. How can we be certain that this is right? The reply is that we cannot. The observations have been made from immense distances, and are consequently liable to certain errors which have been discussed by Colonel Burrard.
It was observed from the following stations:—
| Station. | Height above Sea. | Distance. |
| Shangruti | 17,531 | 78·9 |
| Biachuthusa | 16,746 | 99·0 |
| Marshala | 16,906 | 58·6 |
| Kastor | 15,983 | 66·0 |
| Thurigo | 17,246 | 61·8 |
| Haramokh | 16,001 | 136·5 |
| Kanuri-Nar | 15,437 | 114·3 |
| Barwai | 16,304 | 88 |
| Thalanka | 16,830 | 74·7 |
And apart from the errors due to distance there are others which must always be counted on. As he remarks, no telescope is absolutely perfect; no level is entirely trustworthy; no instrumental graduations are strictly exact; and no observer is infallible. Then, again, the peaks themselves do not always have clearly defined summits, though K2 happens in this respect to be a model for observation, and as it has been observed on several occasions from different stations, the errors in the mean value of height due to faults of observation are, probably, in Colonel Burrard's opinion, less than ten feet. Another source of error is the adoption of possibly erroneous altitudes for the stations of observation. The altitude of K2 was observed from Haramokh and other stations, but the altitude of Haramokh itself may be a few feet wrong, and the altitude of K2 on this account may be thirty feet in error. Another element of uncertainty in determining the height of a peak is caused by the variation in the amount of snow on its summit. There is clearly more snow on the summit of a peak in winter than in summer, and in a hot, dry summer there may be less than in a generally cloudy, snowy summer. A more complicated description of error is introduced by the deviation of gravity from the normal in great mountain ranges. The attraction of the great mass of the Himalaya mountains and of Tibet pulls all liquids towards itself as the moon attracts the ocean. The liquid in levels on the theodolites with which observations of the peaks are made is similarly affected: the plates to the theodolites in consequence cannot be exactly adjusted, and when apparently truly levelled are in reality tilted upwards towards the mountains. At Kurseong, near Darjiling, they would be as much as 51" out of true level and at Mussouri about 37".
MOUNT HARAMOKH, FROM THE ERIN NULLAH
But the most serious source of uncertainty in the measurement of the altitude of a peak is the refraction of the atmosphere. A ray of light from a peak to an observer's eye does not travel along a straight line, but assumes a curved path concave to the earth. The ray enters the observer's eye—I quote from Colonel Burrard—in a direction tangential to the curve at that point, and this is the direction in which the observer sees the peak. It makes the peak appear too high. This refraction is greatest in the morning and evening, and least in the middle of the day; it is different in summer from what it is in winter. One of the great Himalayan peaks visible from the plains of India would appear, from observations with a theodolite made to it from the plains, to fall 500 feet between sunrise and the afternoon, and to rise again 300 feet before sunset; and even in the afternoon, when it would appear lowest, it would still be too high by perhaps 700 feet. This is obviously a very fruitful source of error, and the difficulty of determining the error is increased by the fact that the curvature of the ray varies with the rarefaction of the atmosphere. In the higher altitude, when the rarefaction of the atmosphere increases, the ray assumes a less curved path. All these possible sources of error due to the rarefaction of the atmosphere have been most carefully studied, but even now we must allow 10 to 30 feet as possible error due to the rarefaction of the atmosphere.
