Question: When did the Paris Observatory use the Eiffel Tower as an antenna?
About the article "Eiffel Tower", section "Communications".

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The tower has been used for radio transmission since the beginning of the 20th century.
Until the 1950s, sets of antenna wires ran from the summit to anchors on the Avenue de Suffren and Champ de Mars.
These were connected to long-wave transmitters in small bunkers; in 1909 a permanent underground radio centre was built near the south pillar, which still exists today.
On 20 November 1913 the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained wireless signals with the United States Naval Observatory which used an antenna in Arlington, Virginia.
The object of the transmissions was to measure the difference in longitude between Paris and Washington, D.C. Today, both radio and television stations broadcast their signals from the top of the Eiffel Tower.
Its foundation lies in the ambitions of Jean-Baptiste Colbert to extend France's maritime power and international trade in the 17th century.
Louis XIV promoted its construction starting in 1667, being completed in 1671.
It thus predates by a few years the Royal Greenwich Observatory in England, which was founded in 1675.
The architect of the Paris Observatory was Claude Perrault whose brother, Charles, was secretary to Colbert and superintendent of public works.
Optical instruments were supplied by Giuseppe Campani.
The buildings were extended in 1730, 1810, 1834, 1850, and 1951.
The last extension incorporates the spectacular Meridian Room designed by Jean Prouvé.
The world's first national almanac, the "Connaissance des temps" was published by the observatory in 1679, using eclipses in Jupiter's satellites to aid sea-farers in establishing longitude.
In 1863, the observatory published the first modern weather maps.
In 1882, a astrographic lens was constructed, an instrument that catalysed what proved to be the over-ambitious, international "Carte du Ciel" project.
In November 1913, the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained wireless (radio) signals with the United States Naval Observatory to determine the exact difference of longitude between the two institutions. 
In a notable subtype, the action of all or part of the work centers around the real or threatened destruction of the tower.
1965 In "The Great Race" Jack Lemmon's character Professor Fate misfires a cannon, which causes the tower's collapse at the end of the film.
1981 In the original version of "The Man Who Saw Tomorrow", a prediction of World War III includes the tower collapsing when Paris is destroyed.
1992 In the "Teenage Mutant Ninja Turtles" episode ""Tower of Power", Krang has a giant electromagnet, and wants to use it to pull the Technodrome from its Dimension X asteroid location by using the Eiffel Tower as an antenna.
The Eiffel Tower begins to be pulled loose from its foundations and towards the dimensional portal.
At the last minute, Donatello destroys the generator and the Eiffel Tower falls down to the ground undamaged.
1992 In the "Teenage Mutant Ninja Turtles" episode "Rust Never Sleeps", Bebop and Rocksteady blast metals with Krangs "oxidizer rocket".
The "oxidizer rocket" was originally planned by Krang to use to send the Technodrome to Earth, and when it failed, Krang thinks that it can be used by threatening to rust metal if the people don't surrender to Krang and Shredder.
Even the Eiffel Tower gets blasted, and begins to collapse from rust.
In the end, Donatello reverses Krang's device to turn the metals back to normal.
1993 In the book "The Sweetest Fig" by Chris Van Allsburg, the tower is bent/drooped over from some unknown event.
The tower is mentioned as being repaired/rebuilt to its normal shape later on.
1995 In the real-time strategy game of "Command & Conquer", the tower is one of four selectable targets for the Global Defense Initiative's hijacked Ion Cannon weapon, during the ending sequence of the Brotherhood of Nod campaign.
1996 The tower appears in the Paris level in the PlayStation game "Twisted Metal 2".
The tower can be blown up using a remote bomb and falls as a bridge to other buildings.
1999 In the French Sentai amateur series "France Five", the destruction of the tower in the main objective of the evil empire Lexos, as it generates a barrier around the planet that keeps it from sending armies en masse.
2002 In the 2002 one-shot comic book "The Authority: Kev", the tower is as a missile to destroy an alien flagship.
2004 In "", Kamacuras attacks the tower.
2004 In "", a rocket blows up the tower, and it crushes the Arc de Triomphe.
2008 The History Channel's "Life After People" features the collapse of the tower around 200 years after the disappearance of humans, due to corrosion.
2008 In "Destroy All Humans!
Path of the Furon", the tower (named the "Belleville Tower") is the site of a massive battle against oceanographer Henri Crosteau, who is in a giant squid-shaped robot and nearly destroys it in the process.
The tower can also be destroyed by the player during free roam.
2009 "" depicts the tower being destroyed by a rapidly expanding cloud of metal-eating nanomachines.
2010 In "", a mission begins with a cutscene involving a French news broadcast depicting the tower having collapsed to the side atop several buildings due to massive thunderstorms.
2011 In "", a mission ends with a convoy stopping short of the damaged Eiffel Tower.
An airstrike is called and the Tower topples into the river.  
The Eiffel Towers at Kings Dominion and Kings Island are replicas of the Eiffel Tower in Paris, France.
They opened at Kings Island in 1972 and Kings Dominion in 1975, each when the park originally opened. 
  Gustave Eiffel (1832–1923), engineer and designer of the Eiffel Tower and the Statue of Liberty  Erika Eiffel, an American woman who famously "married" the Eiffel Tower