MargenThe Eiffel Tower is not always the same height. On the hottest days of summer it can be some fifteen centimetres taller than in the depths of winter.
It is made of wrought iron, and metal expands with heat: its particles vibrate more and take up a little more space. When the July sun beats down on its girders, the whole structure stretches a few centimetres towards the sky. As the temperature drops, it shrinks back again.
That same sun, moreover, warms one side more than the other, and the tip leans slightly away from the sunlit side, as if it were looking for shade. Gustave Eiffel designed the tower counting on these movements: a truly rigid building would have cracked. Flexibility is, sometimes, what holds up whatever looks firmest.
Source: Société d'Exploitation de la Tour Eiffel