It was a chilly morning as a gawking crowd has gathered in the courtyard of the École Militaire, on the Champ-de-Mars, in Paris. In a few minutes, in this backyard, a ceremony would take place. Alfred Dreyfus, a young Jewish artillery officer and family man, who had been convicted of treason just days earlier in a rushed court-martial, would be stripped from his insignia medals and would be marched around grounds in his ruined uniform. The date was, 5 January, 1895.
The same morning, not so far from Paris, in the community of Trappes near Versailles, a man in his forties, frozen to his bones, was preparing to launch one more of his balloons up into the atmosphere. He was determined to obtain reliable temperature measurements up to a height of 14 kilometers. His name was Léon-Philippe Teisserenc de Bort, and a few years later he would discover the stratosphere.
The atmosphere is what keep our planet alive. Without it, Earth would be a ball of frozen water and rock with an average temperature of minus 50 degrees Celsius. Life would be impossible.
In the 17th century, new instruments and methods of inquiry, allowed scientists to learn more about the world. The cornerstone of philosophy and science until then was that the space around Earth was filled with different combinations of earth, fire, water and air. This theory was suggested by ancient philosophers, and it was later supported and added to by Aristotle. Isaac Beeckman, a Dutch philosopher and physicist, was one of the first people to realize that air that surrounded Earth had real substance and in the late 1700s, scientists began to launch experiments with balloons and they were surprised to discover that the air was becoming thinner and colder as they rose. This discovery seemed to defy all logic, as the closer you get to a source of heat, that is the sun, the warmer you should feel. Of course, the sun wasn’t any closer to them, in any meaningful way. So, for the next roughly two hundred years, the dominant belief amongst scientists was that the air got thinner and colder until it completely diminishes. At the beginning of the nineteen century this will change.
Léon-Philippe Teisserenc de Bort was born in Paris in 1855. He joined the Bureau Central Météorologique (BCM) immediately after its foundation, and a few years later, in 1892, after spending some time in the French colonies in Africa, studying geology and terrestrial magnetism, he was appointed chief meteorologist. He didn’t last long in the job. Frustrated, because of the centre’s reluctance to understand that the inability to predict weather stemmed from lack of knowledge about the high atmosphere, he resigned in 1896. Thanks to his family fortune, he bought a 3 hectare – site and founded a private meteorological observatory at Trappes, near Versailles. He was now able to devote all his time on his research, to carry out investigations on clouds and the upper air.
In the next two years, Teisserenc de Bort managed to make the first accurate measurements of the height and speed of clouds, first with kites he built himself, and later on with balloons. Until 1902, he launched more than 230 balloons, day and night. Each balloon carried aloft an instrument package, with thermometers and barometers, in a wicker basket. He even designed a parachute system to deploy after the basket released from the balloon, to bring his instrument package gently back down. When evaluating the data recorded, he noticed that the temperature stopped decreasing at an altitude of around 11 kilometres (7 miles), after which it started increasing with height. At first, he thought an error had been occurred, but all the balloons told him the same thing. The air got no cooler. Instead, I was warmed.
In 1902, Teisserenc de Bort published the results of his measurements in a paper, titled Variations de la température de l’air libre dans la zone comprise entre 8 m et 13 km d’altitude. As little as three days later, Richard Assmann, a German meteorologist, made a similar announcement to the German Academy of Science. In his announcement, Assmann was been referring to the existence of an “upper inversion”.
Contrary to until then assumptions, the atmosphere is not a uniform body of air but it comprised of separate layers. Léon-Philippe Teisserenc de Bort called the lower layer, the troposphere, from the Greek word, tropos, which means to turn or stir. Troposphere extends to an altitude of 6 kilometres over the polar regions and 20 kilometres or so, at the equator. It serves as a trap for the water vapour, that is why there is very little water vapour in the stratosphere. Troposphere is the source of all our weather.
He called the upper layer the stratosphere, from the Latin word stratum, meaning layer. Stratosphere occupies the region of atmosphere from about 12 to 50 kilometres; its lower boundary is near to the poles. The rise in the temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the ozone layer which is centered at an altitude of 15 to 25 kilometres. Approximately 90 percent of the ozone in the atmosphere resides in the stratosphere. Both the troposphere and the stratosphere hold together about 99% of the total mass of the atmosphere.
Léon-Philippe Teisserenc de Bort died on January 2, 1913 in Cannes. His discovery of stratosphere was, in the words of the English scientist a generation later, “the greatest ever made in meteorology”. It is also one of the most overlooked events in the history of science.
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