Altitude
2 of the 6 encyclopedias on this shelf carry an entry for Altitude. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
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: Alabama, Che-aw-ha Mountain 2,407 Alaska, Mount McKinley 20,300 Arizona, San Francisco Peak 12,611 Arkansas, Magazine Mountain (?) 2,800 California, Mount Whitney 14,501 Colorado, Mount Elbert 14,436 Connecticut, Bear Mountain 2,355 Delaware, 2 summits near Brandywine 440 Dist. of Columbia, Fort Reno, Tenley 421 Florida, near Mount Pleasant Station 301 Georgia, Brasstown Bald Mountain 4,768 Idaho, Hyndman Peak 12,078 Illinois, Charles Mound 1,257 Indiana, near summit, Randolph Co 1,285 Iowa, 5 miles SE. of Sibley 1,670 Kansas, west boundary, north of Arkansas River 4,135 Kentucky, The Double, Harlan Co 4,100 Louisiana, summits in western parishes 400 Maine, Mount Katahdin (west) 5,268 Maryland, Backbone Mountain 3,400 Massachusetts, Mount Greylock 3,505 Michigan, Porcupine Mountain (?) 2,023 Minnesota, Misquah Hills, Cook Co 2,230 Mississippi, near Holly Springs 602 Missouri, Tom Sauk Mountain 1,800 Montana, Granite Peak 12,834 Nebraska, Plains in SW. corner 5,300 Nevada, Wheeler Peak 13,058 New Hampshire , Mount Washington 6,290 New Jersey , High Point 1,809 New Mexico, peak 2 miles N. of Truchas Peak 13,306 New York, Mount Marcy 5,344 North Carolina, Mount Mitchell 6,711 North Dakota, south part Bowman County 3,500 Ohio, 1 1/2 miles E. of Bellefontaine 1,540 Oklahoma, SW. corner T. 1 R. 1 4,700 Oregon, Mount Hood 11,225 Pennsylvania, Blue Knob 3,136 Rhode Island, Durfee Hill 805 South Carolina, Sassafras Mountain 3,548 South Dakota, Harney Peak 7,240 Tennessee, Mount Guyot 6,636 Texas, El Capitan, Guadaloupe Mountain 8,690 Utah, Mount Emmons 13,428 Vermont, Mount Mansfield 4,406 Virginia, Mount Rogers 5,719 Washington, Mount Ranier 14,363 West Virginia, Spruce Knob 4,860 Wisconsin, Rib Hill (?) 1,940 Wyoming, Mount Gannett 13,785 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. Name Location Feet Aconcagua 23,080 Ararat 17,260 Chimborazo 20,498 Dapsang 28,278 Dickerman 15,766 Elburz 18,526 Everest 29,002 Kenia 19,500 Kilimanjaro 19,600 Logan 19,539 Mauna Loa 13,600 McKinley 20,464 Mercedario 22,397 Mitchell 6,711 Mt. Blanc 15,780 Pike's Peak 14,108 Popocatepetl 17,748 St. Elias 18,024 Vesuvius 14,380 Shasta 4,260 Washington 6,279 Whitney 14,502 See Alps ; Ararat ; Climate ; Snow
Collier's New Encyclopedia (1921)
in mathematics the perpendicular height of the vertex or apex of a plane figure or solid above the base. In astronomy it is the vertical height of any point of body above the horizon.
What Has Changed in the Last Century
Aiton's 1910 figures were the best barometric work of their day, and the entry is candid about the problem: readings at Lake Balkash differed by 680 feet between summer and winter. Satellite geodesy has since settled most of it — Everest's 29,012 feet became 29,032 in the joint China–Nepal remeasurement of 2020, and Alaska's Mount McKinley, listed at 20,300 and 20,464 feet on the same page, is now fixed at 20,310 and was officially renamed Denali in 2015. Everest was first climbed in 1953 and has since had thousands of summiteers, along with the crowding, litter and death tolls that turned high-altitude climbing into an ethical argument. The old claim that plant life ceases above 15,000–18,000 feet at the equator has also softened: mosses and flowering plants have been recorded well above 20,000 feet in the Himalaya, and Peru's La Rinconada, near 16,700 feet, is now generally called the world's highest permanent town.
Written for this edition, 2026.