Celestial Globe - Expo Paris 1889
Along the Avenue de Suffren, under a simple dome covering a modest building, is one of the most curious attractions of the Universal Exhibition. It is only a globe, but a globe with a circumference of 40 metres.
It is claimed that the earth is exactly 40 million metres in diameter. But this claim is not absolutely true, because every time we measure our planet again, the size changes. So the simplest thing to do is to rely on general opinion and the standard metre, which is on deposit at the Conservatoire des Arts et Métiers. Under these conditions, the globe on Avenue Suffren, with a circumference of 40 metres, represents the earth to the millionth and its diameter is approximately 12.70 metres, taking into account the flattening of the poles.
It is by far the largest terrestrial globe ever built, and its dimensions have made it possible to trace all the geographical accidents and political divisions of the earth. This is even on a rather large scale, since it is only 12 or 13 times smaller than the staff map. Paris is about one centimetre square and if we had wanted to show the Eiffel Tower in relief, it would have been about a third of a millimetre thick, as seen through a microscope. As for Mont Blanc, it would have been four to five millimetres thick, and the Gori-zankar would have been almost a centimetre thick. As it stands, this globe is very interesting. Much more than a map, even on a large scale, it gives the impression of truth. It is extremely difficult to make a child, who has just been told that the earth is round, understand that this round earth is represented on a flat piece of paper. The globe alone is within the reach of his intelligence. And how many are still children on this point. Also, there is a real attraction in making, by the spiral ramp that surrounds it, not just one tour, but several tours of the world in well under eighty days... This tour can also be made by remaining motionless on any point of the ramp, the globe is in fact animated by a rotational movement, which is communicated to it by a crank that one person can move. Apart from the translational movement of the earth around the sun, the astronomical demonstration is therefore as complete as the geographical demonstration.
To accomplish this rapid journey, one begins by climbing the staircase in one of the pavilion's entrance turrets, or better still, by taking the Ottis lift in the other turret. This brings you to about the height of the Arctic Circle, where there is a grandstand with bleachers. From this stand, the helix ramp descends to the South Pole. For the northern polar section, a tripod bridge is used, which is supported by the rostrum and the propeller path.
Now let's see how this monster globe is made.
The ordinary spheres, which the trade sells for geographical studies, are simple cardboard globes composed of two or more parts, stamped on a given template, then joined together, and on which are glued, once the assembly is done, spindles of paper printed and coloured beforehand. It is easy to see that if the spindles are of a certain size, they cease to offer mathematical accuracy, since they are flat surfaces that are forced to cover curved surfaces. This can only be achieved by cheating a little. But for small globes, this is of little importance. In the case of larger globes, the spindles are split into various pieces instead of running from one pole to the other. After gluing, the whole surface is varnished, and if the joints have been well made, it appears to be a single whole.
But a 40-metre globe could not be built so lightly. First of all, it was necessary to establish an iron framework with angle iron, and to constitute this framework, there are 20 half-meridians and 5 parallel circles also made of angle iron.
At their two ends, these half-meridians are connected to a ring two metres in diameter; from the southern ring to the northern ring, a straight angle iron joins the two ends of each curved angle iron and maintains the curve, the stability of which is further ensured by a series of angle irons which, starting from various points on the half-meridian, are fixed along the straight angle iron.
Finally, two flat irons, each of which extends from a ring to the second opposite third of the half-meridian, complete this extremely light and solid assembly.
This system is repeated twenty times and constitutes the bulk of the globe's framework. The other half-meridians and parallel circles that are part of its construction only serve to support the surface panels.
These panels are 585 in number; they are rigorously curved, according to ten different templates which correspond to the height that these panels must occupy between the meridians. They are made of spherical cardboard, coated with a mixture of Meudon white and skin glue. These panels, cut and calibrated, are fixed on wooden frames, then these wooden frames are screwed on wooden fittings, with which the meridian panels are equipped.
Before this assembly operation, each panel was painted in oil. Excellent tracings were first made according to the most complete and recent documents and then transferred to the panels, on which the painters finally translated the relief of the ground with light effects and the appearance of the different regions with different shades, while at the same time recording all the details of physical and political geography.
The tracing operation had the very disadvantage that we mentioned in connection with commercial globes, the transport of a flat drawing on a spherical surface. This was remedied by having the tracographs work on curved boards, the surface of which represented exactly a fraction of the globe, and the proportions were thus exactly maintained.
The promoters of the 40-metre globe, Messrs Th. Villard and Gh. Gottard have accomplished a very interesting work and it is understandable that their project, from the beginning, gathered high approvals and obtained the patronage of eminent personalities.
It is also understandable that it did not have all the success it deserved, for one has to pay a franc to enter the pavilion, and the majority of people who go to the Exhibition as to the fair, would rather spend twenty cents to see the belly-dance than to learn geography.
©Livre d'Or de l'Exposition - Alfred Grandin.