It has been asked what the amplitude of the oscillations of this gigantic tower at the top would be under the action of hurricanes. Mr. Max de Nansouty, who has made a long series of calculations on this subject in his interesting work on the 300-metre tower, and the Academy of Sciences, which has dealt with the same question, declare that the greatest oscillations at the top will not exceed 10 centimetres in the most unfavourable storm conditions. If any visitor seeking the thrill of the cyclone remains at the highest peak during the storm, it is certain that he will not even notice these oscillations.
For what reasons was iron used?
The idea of building a colossal tower was not new;
In 1832, the English engineer Trevithick proposed to build a monument of 1,000 feet (304m,80); the Americans repeatedly forced the same project; but what distinguishes the Tower of 1889 from all those which were projected before it, is its mode of construction, the use of iron to the exclusion of all other materials, and its assembly by processes which are due exclusively to M. Eiffel.
The Tower is composed entirely of very strong, very elastic and very light iron lattices, assembled by riveted iron gussets. This is what gives it its airy, lace-like appearance, an appearance that left even those who had originally doubted the beauty of the work moved and pensive,
For several reasons, iron was the only material that could be used to build such a colossal work.
For several reasons, iron was the only material that could be used to build such a colossal work. In the first place, antiquity, the Middle Ages and the Renaissance had pushed the use of stone to its extreme limits of boldness, and it hardly seemed possible to go much further than our predecessors with the same materials. Moreover, stone offered much less resistance to wind than iron or steel; and finally, since masonry gave no precision in calculations, it was impossible to carry out these grandiose projects, even with a combination of masonry and iron.
Iron, on the contrary, was indicated by the great resistance of this metal under a low weight; by the small surface which it allows to be exposed to the wind; finally, by its elasticity which solidifies all the parts and makes it possible to make an assembly of which all the parts are likely to work with the extension or the compression, and which, being all calculable, can give a complete safety.
Metal has one last advantage: it is that the construction is "removable"; without excessive expense the Tower could be moved, if it were deemed useful to transport it to another part of Paris. If the State, owner of the Tower, decided tomorrow to move it to the top of the Butte Montmartre, the operation would be very simple and M. Eiffel estimates the cost of this move at G or 700,000 francs.
The weight of the Tower.
The weight of the tower with all its accessories, floors, constructions, etc., is estimated at nine million kilograms.
This enormous load is distributed over a surface of foundations such that the pressure exerted by it on the subsoil does not exceed 2 kilograms per unit of surface. A solid wall, made of millstone, nine metres high, built in Paris, does not press any more on its foundations.
The total weight of the iron used is 7 million kilograms.
The weight of the iron rivets that connect the pieces together is about 450,000 kilograms; their total number is 2,500,000; of this figure, 800,000 were installed by hand on the site of the tower itself.
The number of metal parts criss-crossing each other in all directions is 12,000 and each of them, because of their shape and their constantly changing direction in space, required a special design. It is therefore the enormous mass of 12,000 drawings that came out of the design office of the Eiffel factory in Levallois-Perret, calculated by logarithms, with a precision of one tenth of a millimetre: a mountain of drawings prepared this mountain of iron. And in all of this, as the official reports of the Exhibition's control service show, there was not a single uncertainty or error.
Utility of the Tower.
The Eiffel Tower is above all the realisation of a gigantic industrial work in the order of the construction of bridges, viaducts or lighthouses. A saving lighthouse, a useful bridge will certainly be the consequence of these boldly executed works before which human science has so far shrunk. It is therefore, from this special point of view, full of lessons for the future.
But this is not its only role: and there are few scientists who do not think, since the completion of the Tower, of carrying out some experiment more directly related to the object of their studies. It will thus be for all an observatory and a laboratory such as has never been placed at the disposal of human intelligence.
Astronomical observations. - A telescope of great aperture, installed at the top of the Tower, would make it possible to follow the stars which only reach a low height on the horizon of Paris. In addition, the purity of the air and the absence of the low mists that most often cover the Observatory will facilitate many studies that were thought to be impossible in our region.
Scientific observations. - Having for the first time, apart from the unstable and spinning gondola of a balloon, a free and vertical height of 300 meters, we will be able to complete work that has been going on for a long time, among others:
The fall of bodies in the air;
The resistance of air at different speeds;
The laws of elasticity;
The study of the compression of gases or vapours;
The study of the oscillation of the pendulum; The rotation of the earth, etc., etc.
On the subject of the rotation of the earth and the Tower, the Journal du Ciel gave, a few months ago, curious details.
The top of the Tower, says M. Minary in this note, will make in one day, as a result of the rotation of the earth, a circumference of 300 metres in radius, that is to say l,884m,96 more than its foot. A rotation of the earth lasting 23 h. 56 or 1,436 minutes, or 86,160 solar seconds, it follows that the top of the Tower makes per second l,884m,96 : 86,160 or 0m,02187, or nearly 22 millimetres more than its foot. Now, a lead ball to fall freely from the top of the Tower, having to take a number of seconds equal to the square root of the double of the height divided by the intensity of gravity, i.e. the square root of 600 : 98.088 "will take 7 seconds 8, and in this interval, the top of the Tower will be 0.02187 x 7.8 or 0m.17 more than its foot on the eastern side. It follows that if the floor of each floor of the Tower is pierced with three holes at 25 centimetres distance on lines running north-south, and situated vertically one below the other, by passing through the extreme holes two plumb bobs (steel wires of one millimetre diameter) reaching down to the ground, the lower ends of these wires will draw, on a large and solid cast-iron plate placed underneath, the direction of the meridian over a length of 50 centimetres. The holes in the middle, lengthened more and more on the eastern side, will give passage to a lead ball from minute to minute, and the deviation of 17 centimetres towards the east due to the rotation of the earth can be seen each time by the point where the ball strikes the cast iron plate to the east of the two plumb lines.
M. Minary adds that by receiving the lead ball in a suitably shaped vase, amateurs will have the added advantage of being able to observe the transformation of the movement into heat, without burning their hands, because the heating of the ball, although appreciable, will not exceed 22 degrees.
Meteorological observations. - From the point of view of hygiene and science, one can usefully study The direction and violence of atmospheric currents; The state and chemical composition of the atmosphere; Its electrification;
Upper currents; Lightning;
The temperature at different heights of the Tower and at different times of the day; The hygrometry of the atmosphere, etc.
Strategic observations. - In case of war, one could, from the top of the Tower, observe the movements of armies within a radius of more than 70 kilometres, over our defensive forts.
In the event of a siege or investment, constant communication would be assured between Paris and the départements by the electric fires with which the Tower is equipped. Optical telegraphy would make it possible to communicate with Rouen, Beauvais, Orleans, Alençon, etc.
This is certainly not one of the least useful aspects of this unique monument across the globe.
The future will tell us what lessons will be learned in the execution of this colossal construction: but the information predicted and foreseen by the scholars of all nations will certainly be considerable. The crowd feels this, and has always shown warm sympathy to Mr. Eiffel.
In the meantime, we must congratulate the author of this great enterprise: he has proved to the whole world that France is a great country, with bold conceptions, and that it is still capable of succeeding where others have failed. The Americans said in 1874 of the Philadelphia Tower: "We shall celebrate our centenary with the most colossal iron structure that man ever conceived. Their tower was not completed, while these words, which in America remained a dead letter, became a living reality for France.
Paris now possesses a triumphal arch more colossal than any which the peoples have dreamed of for the conquerors, and this superb monument is raised to the glory of modern science for the greatest honour of the French.
© Guide Bleu du Figaro et du Petit Journal 1889