The Eiffel Tower Is Taller in Summer
Iron expands when it warms, so the tower quietly grows about 15 centimetres between a cold January and a hot July, and leans away from the sun while it does it.
The Eiffel Tower is not one height. It is a range. On a hot July afternoon it stands roughly 15 centimetres taller than it does on a cold January morning, and nobody has to do anything to make that happen.
The reason is the same one that loosens a jar lid under hot water. The tower is around 7,300 tonnes of wrought iron, and iron expands when it warms. The change in any single beam is far too small to see, a fraction of a percent, but the tower is more than 300 metres of beams stacked end to end, and small fractions of a very large number add up to about the width of a hand.
It also leans, which is the better part. The side facing the sun warms faster than the shaded side, expands a little more, and pushes the top away from the light. Over the course of a day the summit traces a slow, lazy loop as the sun moves around it, drifting a few centimetres at a time. Visitors standing up there notice nothing whatsoever. The tower is simply leaning away from the afternoon like someone edging out of a conversation.
None of this is a flaw. Big metal structures are built to move, and this one sways gently in high wind as well. A tower that could do none of that would be far more worrying than one that quietly stretches every summer.
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