Figure by Djexple, Wikimedia Commons
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Longitude is a geographic concept that locates a site’s position either west or east from a designated starting line called “the prime meridian.” The prime meridian (longitude = 0.0000), by international agreement, is the north-south, pole to pole line that runs through Greenwich, England. Lines of longitude are marked every degree around the roughly spherical Earth. To the east of Greenwich, there are 180 degree lines and to the west there are another 180 degree lines. The 180 degree latitude line where these two subdivided systems meet (which is, then, on the directly opposite side of the globe from the Prime Meridian) roughly serves (with a few jiggles and jogs due to politics and the overall distribution of people) as the “International Date Line.”
Longitude and the time of day are directly related: 15 degrees of longitude corresponds to an hour of clock time. The “time zones” of North America, then, are roughly divided up by north-south lines that are approximately 15 degrees of longitude apart.
Determination of longitude was a complex but absolutely essential task that was eventually made possible by the invention of very accurate clocks. Someone on a sailing ship could then compare the time of a known latitude location (typically the Prime Meridian) with their site’s determined clock time and calculate the longitudinal difference between the Prime Meridian and their location.
Figure by Swid, Wikimedia Commons
One very famous line of longitude is the 100th Meridian (west). This line runs through the center of North America. As it crosses the United States it roughly bisects North Dakota, South Dakota and Nebraska, and then cuts through the western third of Kansas. It then crosses the Oklahoma panhandle and forms the border between Texas and Oklahoma as the eastern edge of the Texas panhandle. It then continues down through the middle of Texas into Mexico.
Climatologically, the 100th Meridian (west) marks the western edge of the typical movement of moist air coming off of the Gulf of Mexico and the eastern edge of the great rain-shadow of the Rocky Mountains. It is roughly the line where the average yearly rainfall equals 20 inches (51 cm). It is, therefore, the boundary between the moist ecosystems of the American East and the dry ecosystems of the American West. It was first defined as this border by John Wesley Powell in 1878.
John Wesley Powell (National Portrait Gallery), Photo by B. Hathorn, Wikimedia Commons
John Wesley Powell was an iconic American figure of the Nineteenth Century. He was also the possessor of one of the great beards in American history! Powell was a war hero in the Civil War (and lost part of his right arm in the Battle of Shiloh). He was a geologist and a college professor, an explorer who mapped great parts of the west and the first man to go down the Colorado River through the Grand Canyon. He was the second director of the U. S. Geological Survey and the first director of the Bureau of Ethnology at the Smithsonian Institution.
The following quote is from an article Powell wrote in 1890 for Century Magazine based on his earlier testimony before the Senate Select Committee on Irrigation and Reclamation of Arid Lands in which he describes the 100th Meridian:
Photo by J. Penry, Wikimedia Commons
“Passing from east to west across this belt a wonderful transformation is observed. On the east a luxuriant growth of grass is seen, and the gaudy flowers of the order Compositae make the prairie landscape beautiful. Passing westward, species after species of luxuriant grass and brilliant flowering plants disappear; the ground gradually becomes naked, with bunch grasses here and there; now and then a thorny cactus is seen, and the yucca plant thrusts out its sharp bayonets.”
Powell tried to get the Senators to see that the American West was a fragile place, a place delicately balanced between its scant available water and the biological use of that water. He proposed a very controlled and highly regulated settlement and development of the West. He was, though, unsuccessful in convincing the Senate not to follow the expansionistic philosophy of Manifest Destiny. The prevailing idea concerning development of western lands, with no supporting scientific evidence, was that “rain will follow the plow,” and that by opening the West to uncontrolled agricultural development, the action of breaking open the soil would lead to increased rainfall and sustained production of crops.
It is interesting that although politicians and developers worked hard to convince the public of the agricultural potential of the West, private companies that insured farms or lent money for their purchase and management were very reluctant to do so. There is a roadside sign in South Dakota that marks the position of the 100th Meridian. The sign states, “For two generations the Insurance Companies and other worldwide lending agencies would not, as a matter of agreed policy, lend a shiny dime west of this line.”
Dust storm in Texas, 1935. Photo by NOAA, Public Domain
Development did happen, though, and the human and ecological tragedy of the Dust Bowl followed in the 1930’s. The degradation and erosion of once productive lands was the cost of ignoring the scientific advice of people like John Wesley Powell.
Before I move on from Powell, I must say something about the darker side of some of his research and writings. Powell was a strong advocate for the “civilizing” of Native Americans in the West. He used his ethology articles and books to encourage government-sponsored programs designed to destroy the traditional Native American ways of life. Conversion to Christianity, the exclusive use of the English language, and the adoption of European methods of farming and commerce were, to Powell and most of his fellow ethologists of the time, critical to advancing the lower caste, “barbaric” Native American people to higher levels of existence. Powell’s wisdom regarding land use policies and outcomes has to be balanced against his racist attitudes toward Native Americans. For a more detailed discussion of the “scientific racism” espoused by John Wesley Powell, please see the article in the September 9, 2019 issue of Scientific American.
(Next week: more on the 100th Meridian and where the “Climate Meridian” might be located today!)
Just excellent! Thank you.
rjw Don’s brother