That is the Eiffel Tower, which was, for 40 years, was the tallest building in the world, and it has just welcomed its 250-millionth paying visitor, and it is the most visited commercial monument in the world, and it was built by this chap here, Gustav Eiffel. Eiffel was an engineer, a young, not very well-known engineer, who had already built a number of very daring and radical railway bridges, and he put in a bid to build this thing. Now, he only had a 20-year lease, and he felt that his building, which we all agree is a magnificent thing, although at the time it was not thought, his building should last for much longer than that, so he set out to turn it into a scientific laboratory. As he said, his tower will be “an observatory and a laboratory such as science has never had at its disposal”.
It is a striking building. If you look at it, it is made of wrought iron, which is light and strong. In fact, if you take the mass of the volume of air that is trapped within the Tower, and you weigh the air, and air does in fact have a weight of course, if you were to weigh that volume of air, the air would weigh more than the metal that went to make the Tower. The Tower is 25 metres square at the base, and if you were to take all the metal in the Tower and melt it into the base, how deep do you think it would be? It would be six centimetres deep – that is all. So, it is an extraordinary work of engineering, and even in 100 mile an hour wind, the top only moves by about six centimetres, so clearly, Eiffel had a triumphant piece of engineering that the French have now and of course are very proud of it.
Eiffel set out to make his Tower into a scientific laboratory, and he spoke specifically of memorialising the great scientists of the day, of the Revolution, and he did it in various ways. For example, there is inscribed on the Tower the names of 72 scientists, not that you can read them. Some of them are perhaps more familiar than others, but there is: Cuvier, who was the founder of palaeontology in revolutionary years; Laplace, who was an astronomer and mathematician and really gave us our understanding of the solar system; there was Lavoisier, the founder of chemistry, who we have already talked about; Ampere, the great electrician. That is just a few of them. There are many, many more. There are many more highly familiar names there.
Eiffel set various things up in his Tower. The Eiffel Tower was the site of the world’s first working wind tunnel, amazingly enough. It was in the base of the Eiffel Tower. There is the wind tunnel, with the Tower above it, and it was used in the very earliest tests of wings for aircraft flight.
The Eiffel Tower was also the site of the first real research in aerodynamics, and what Eiffel did was to drop weights down long wires from the top of his Tower and measure how fast they travelled, with a vibrating tuning fork, and what difference the shape and the size of the mass had when it was faced with air resistance. Here he is, on his Tower, on the drop-test experiment.
Various other things were done at that time and then later. Amazingly enough, just five years after it was built, the first cosmic rays were discovered on the Tower. Because Marie Curie had discovered radiation, people became interested in radiation, and people realised really quite soon that if you had a radioactive source here and you went 300 metres away down the road, the amount of radiation you measured would be less than on the source, and soon after the discovery of radiation, somebody had the bright idea to say, “Alright, what happens if you have a radioactive source at the bottom and we climb 300 metres up to the top of the Tower – is it the same effect?” They expected it would be the same effect, but it was not. There was too much radiation at the top of the Tower – it did not decrease as much. What was happening, in fact, was that cosmic rays were coming in from space, originating from the Big Bang in the end, and they were discovered on the Eiffel Tower.
The Eiffel Tower was the site of the world’s first radio broadcast. It had, in 1906, a radio aerial put on its top and messages were sent, and in 1914, the radio aerial was there and it picked up some secret radio messages by the German Army, which was then invading France, that they were planning an attack on Paris immediately, and, famously, the French troops used taxis, Paris taxis – I am sure they tipped the drivers well – to get the Valley of the Marne where they held the Germans back, so the Eiffel Tower saved Paris.
So, it has done many things. It has also become an image, an icon, of Paris, of France itself, and there are various famous pictures of it. This is perhaps one of the more famous. This is the tallest building in the world, the Eiffel Tower, struck by lightning in 1890.
There is an extraordinary series of coincidences that link the issue of lightning to the French Revolution itself and to the downfall of many of the scientists who were involved in it.
So, that is lightning. We all know a lot about lightning, and we all believe, do we not, that Benjamin Franklin actually invented the lightning conductor. Many people had been killed by lightning. Thousands of people were killed by lightning. Paris passed a law forbidding bell-ringers to ring the bells during lightning storms in case it was struck. Some people thought that the bells actually attracted the lightning – they were wrong there. But, literally, thousands of people every year were killed by lightning in Europe. Franklin, famously, is said to have put a kite up in the air, with a key on it, and a wet string which would carry electricity coming down. If that had been struck, he would have been killed instantly, so we know he did not do it because he came back from the experiment. However, he had written a book called “Experiments on Lightning in the City of Philadelphia”, and in the book, he described this experiment, that it would be an interesting thing to do.
Now, Louis XV, the penultimate monarch of Paris, who was a highly intelligent man, as indeed was his son, Louis XVI, read this book and was fascinated by it, and he asked some of his scientists to demonstrate some of the ideas that were there. Well, the people involved, the scientists involved, Buffon, who was a naturalist, and Dalibard, who was a botanist, felt they better practise before they tried it in front of royalty, so they set up the world’s first lightning conductor, in what is now a western suburb of Paris, Marly-la-Ville, in 1752, and there it is. At the bottom, you can see a rather gingerly-looking man in a cloak, with an iron bar, baton, in his hand, and the idea was to wait until the storm clouds passed overhead and to hold this baton some distance away and see if any sparks crossed the gap, and the answer was, yes, they did, whereupon the terrified experimenter, who had been well-paid to do this, ran away screaming, but that was the world’s first lightning conductor. That was the first place where it was actually done.
You can go to the Eiffel Tower and you can look out over the landscape of Paris, the landscape of the Tower itself, and see many other sites where world-firsts took place. I will just mention a couple of them before I get onto the main body of the talk.
The site of the Eiffel Tower was where the world’s first hydrogen balloon was set off. It was set off with hydrogen, and how to make hydrogen had been discovered by Lavoisier, who poured nitric acid onto scrap iron and that generated hydrogen. That was the first hydrogen balloon, from there. If you looked across to the north, you see the Palace of Luxembourg and its beautiful gardens. In revolutionary times, they only had one plant growing in them, and that was – there is the chap, Parmentier, holding the plant – it was the potato.