Altitude

in geography the perpendicular height of a locality above the sea-level. The greatest known altitude of any point on the earth's surface is the summit of the Himalaya mountains. The top of Mount Everest rises 29,012 feet above the Indian Ocean. The greater part of the land surface lies below the line of 2,000 feet. High altitudes have much the same effect on climate as that produced by arctic conditions. The temperature falls three degrees for each 1,000 feet of elevation. Even at the equator plant life ceases to exist at a height of 15,000 to 18,000 feet above the sea. The tops of the highest equatorial mountains have an arctic climate without even the short arctic summer.

The highest inhabitated spots in the world are: a mining district in Chile, 18,480 feet above the level of the sea; a mining district in Peru, 16,200 feet, and a monastery in Tibet, 15,200 feet. The highest home of man in the United States is the Pike's Peak observatory in Colorado, 14,250 feet above sea-level.

The following table was contributed to the June, 1909, issue of the National Geographic Magazine by N. H. Darton of the United States Geological Survey. The data are from maps of the United States Geological Survey, unless otherwise stated. The height is given in feet:

Authorities differ as to the height of prominent mountains. In the case of a mountain as well known as Mt. Blanc, the height is given all the way from 15,779 feet up to 15,810 feet. Altitudes are determined chiefly by barometric observations. Allowance must be made for temperature. Barometric readings for Lake Balkash in Siberia, for instance, made in midsummer, indicate an altitude 680 feet below that obtained from a midwinter reading. It is not strange that tables of altitudes exhibit discrepancies.

HEIGHTS OF NOTED MOUNTAINS.

See Alps; Ararat; Climate; Snow