Scientific experiments at the Eiffel Tower

How the Eiffel Tower was a science lab?

Tuesday 3 December 2019

Modified the 03/12/19

From its inauguration, the Tower has played host to a variety of scientific experiments that made it a real laboratory. But why? By Bertrand Lemoine.

As soon as it was inaugurated 1889, Gustave Eiffel was already thinking about how to demonstrate its usefulness. He had obtained a 20-year concession from the City of Paris to use the land on which it was built. This meant that after 1909 its future would be uncertain and depended upon the Paris City Council’s decision. In addition, Eiffel was fascinated by the scientific progress of his era. He had the names of 72 men of science carved into the edge of the first floor to honor them and to symbolically put the Tower under their protection. symbolique.

High-flying experiments! 

Right away, the Tower’s height lent itself to very particular experiments. A large version of Foucault’s pendulum was attached the underside of the second floor. The oscillations were amplified by their length and thus able to substantiate the forces that govern the Earth’s rotation. A 300-meter-high, free-air, mercury pressure gage allowed for the exact measurement of high pressures, and was used to calibrate the metallic or gas pressure gages used in industry. They also attempted some physiological experiments related to altitude, but these were not really conclusive. One of Eiffel’s first initiatives was to install a weather station, with the physicist Éleuthère Mascart, at the Tower’s summit, as he had done on his different properties. The results of daily measures of temperature, atmospheric pressure, humidity, rainfall and windspeed were published by Gustave Eiffel at his own cost. In this way he contributed to the advancement of this young science by demonstrating the value of collecting this data over long periods of time.

Laboratoire de recherche sur la chute des corps

The effects of wind and resistance

Eiffel had to contend with the wind throughout his building career. The Tardes Viaduct was hurled into the chasm during a storm in 1884, while it was under construction. Even though his openwork structures don’t look like they would put up much resistance to the wind, its effects could be devastating. To better understand the wind’s effects on his work, Eiffel had measurements carried out to evaluate the pressure the wind exerted on his structures depending on its speed. Then, between 1903 and 1905, he had a vertical cable strung between the second floor and the ground, so that objects of various shapes and sizes could slide down its length. A clever system of measurement was attached to the objects themselves, which evaluated the wind resistance they encountered as they were allowed to free fall down the cable. 

Later, in 1909, Eiffel had an aerodynamics lab built at the foot of the Tower so they could blow air onto fixed objects instead of letting them fall, making it much easier to take measurements and vary the wind speed. Thus, the Tower and its laboratory contributed to the development of aerostation, and the early days of aviation. In 1912, the wind tunnel was transferred to a permanent building in the neighboring 16th arrondissement, rue Boileau, where it is still in operation. 

A giant antenna

However, it was radio that made the Tower a key site for scientific experiments. Soon after wireless telegraph transmission was invented at the end of the 19th century, the military took a special interest in the technology. The Tower offered an amazing opportunity for its experimentation, because the higher the antenna, the greater the distance and the wider the zone over which messages can be transmitted. An antenna cable was installed, stretching from the summit to the Champ de Mars. En 1898, Eugène Ducretet was able to communicate with the Pantheon 2.5 miles (4 kilometers) away. So in 1903, Eiffel offered to let the Army use the Tower, and even to finance a part of the necessary installations himself. In 1904, they were able to communicate with the forts in the East and even with the Bizerte naval base in Algeria. From that moment, the Tower gained strategic military importance. This allowed Eiffel to extend his concession on the land for another 70 years, which guaranteed the long life of his Tower. It has never been questioned since!

Bertrand Lemoine is an architect, engineer and historian. He was a research director at the CNRS and general manager of the Atelier International du Grand Paris. He is an internationally recognized specialist in the history and current events of architecture, construction, the city and heritage in the 19th and 20th centuries, particularly in Paris, Greater Paris and the Eiffel Tower. He is the author of forty-three books and several hundred articles on these subjects. He is currently a consultant on architectural, urban, digital and energy issues.

Photo Bertrand Lemoine

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