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The first experimental radio transmission from the tower was in 1898 when Eugene Ducretet, at the Pantheon, received signals from the tower. In 1889, Eiffel began to fit the peak of the tower as an observation station to measure the speed of wind. He also encouraged several scientific experiments including Foucault's giant pendulum, a mercury barometer.

Eiffel and Aviation

After Eiffel had experimented in the field of meteorology, he began to look at the effects of wind and air resistance, the science that would later be termed aerodynamics. This field has become a large part of military and commercial aviation as well as rocket technology. Gustave Eiffel imagined an automatic device sliding along a cable that was stretched between the ground and the second floor of the Eiffel Tower. In 1910, using the Eiffel Tower as a test platform, he achieved remarkable experimental results in measuring the wind resistance of a flat plate.
Wind Tunnel Testing
The limited capacity of the available measuring instruments led Eiffel on a quest for a more sophisticated knowledge of aviation and, eventually, to wind tunnel experiments. He built a wind tunnel on the Champ de Mars, which was in use from 1909-1911. The tunnel was sufficient for lab experiments but inadequate for the study of airplanes. However, with the help of several other engineers, Leon Rith and Lapresle, Eiffel made over 5,000 tests in this lab. Almost all the pioneers of aviation conducted tests in this wind tunnel.
Fighter Plane Design
A better wind tunnel, which is still in use, was built between 1912-1914. Here, Eiffel began experiments with military equipment for WWI fighter planes. In 1917, the Eiffel Laboratory designed a very advanced monoplane fighter of which two prototypes were built in Breguet. One crashed due to pilot error.

Eiffel was a contemporary of Samuel Langeley, the president of the Smithstonian Institute, for whom the NASA's Langely Research Center was named. Much of Eiffel's work had gone on to help expand the science of aerodynamics. NASA used many propeller and wind tunnel experiments in their trainer planes for astronauts.

Leading European Authority on Aerodynamics
Eiffel was the leading European authority on the aerodynamics of high frames [he wrote "The Resistance of the Air" in 1913]. In the construction of the Eiffel Tower, the curve of the base pylons was precisely calculated so that the bending and shearing forces of the wind were progressively transformed into forces of compression, which the bents could withstand more effectively. Such was Eiffel's engineering wizardry that even in the strongest winds his tower never sways more than 4-1/2 inches. The super skyscrapers erected since 1960, such as the World Trade Center, were constructed in much the same way.

Died
He died on December 27, 1923 at the age of 91. In 1964, the tower was registered as a Parisan historical monument. Eiffel's descendants founded the Fondation Gustave Eiffel in 1995.