Close your eyes and picture the city of Paris．Now imagine the city without its most famous landmark：the Eiffel Tower．

The unthinkable almost happened．

When French engineer Gustave Eiffel built this tower for the Paris World’s Fair of 1889，it was controversial．The iron structure contrasted(对比)sharply with the historic stone buildings of Paris．Eiffel’s four-legged iron archway was supposed to last only 20 years．That’s when Eiffel’s permit to operate the building would expire(过期)and the city could choose to tear it down．

Yet from the beginning．Eiffel had a strategy to save his building．If the Tower was linked  to important research，he reasoned，no one would dare to take it down．So he would make it a  grand laboratory for science．

Scientific research began just one day after the Tower opened to the public on May 6，  1889．Eiffel installed a weather station on the Tower’s third(and highest)floor．He connected  instruments by wire to the French weather bureau in Paris．With these，he measured wind speed  and air pressure．