I) The dome of the observatory of Nice   

              In 1884, interested by the creative qualities of the manufacturer of Levallois-Perret,  patron-banker Bichoffshein asked Gustave Eiffel to design the dome of the observatory of Nice, but Eiffel was not the only applicant. How did he win agreement?

First of all, on May 21st, 1881,  specifications were sent to twenty builders: seven projects were deposited. Gustave Eiffel’s project, considered too innovative, was  classified only second; it however held the attention of the Admiral Blow and of the architect Garnier, who rebelled against the decision of the Committee. The controversy got worse and on the Admiral mouchez’s initiative the community of observatory pronounces, on the  February 10th, 1883, for Gustave Eiffel's project. The latter has assured the functioning of this dome during ten years.

     Bichoffshein, financier, owner and maitre of works, chose Garnier as architect and,so,give to Gustave Eiffel, the building of the" big equatorial " of 16 metres tall and his dome. So Garnier,for reassure the worried, reintroduced in the project of Eiffel the ball bearing’s process, by keeping the annular ballcock. Indeed this solution give an alternative of help in case of breakdown.Gustave Eiffel's system was attractive but actually raised two problems: the first one concerned the staircase of observation, on which the astronomer would stand: it must be able to move everywhere on the floor along with the dome. Staircase and dome, indeed, had to be bound together. The second   problem  was the weight of the dome: 162 tons had to be relieved but it was also necessary to avoid the risk of deformation; Eiffel, consequently, got rid of the frictions between  mechanical parts by making the dome float on the annular tub. Naturally, this tub is filled with an appropriate liquid, potasium carbonate; therefore, the lower ring of the dome once stiffened, got indeformable; the base was not sensitive to possible collapses in the wall because it was liquid. Eiffel also found another way of relieving the dome by building it out of steel.

    The movement of rotation of this dome is made by a crank, but it can also be operated by a clock machinery which offered the advantage of operating a round in five minutes. The staircase of observation was articulated on a platform which rose on pebbles, which enabled it to revolve in a circle of 9 metres in diameter around the dome. In five minutes, the staircase rose from the ground up to the summit. The opening system amazed comtemporaries by its modernism: two doors ,placed along the height of the dome moved of 1.50 metres apart, opening a free space of 3 metres in width, in the dome.

 GASCARD simon