It was necessary to decide on the choice about the
dome which was to crown the building that Garnier had designed like
a real scientific Temple, and which had to shelter the main instrument
being under construction: the large 76cm-refractor.
Gustave Eiffel was
offered to do it in 1884. First, he submitted to the Paris Observatory,
the project of a dome, moving by an ingenious system of floating on a concentrated
dissolution of chloride of magnesium, able to shelter a future
planned 74cm- refractor.
The director, Mouchez and the Council of the Institution
unanimously approved it, but the expert committee designed by the
Public Ministry of Labour, rejected it without appeal.
Within the committee, Mouchez and Garnier were enthusiastically defenders of this "revolutionary" system . They had no difficulty to make adopted by Bischoffsheim for the large refractor of Nice. Bischoffsheim knew Eiffel's art and inventive genius who had built the large railroad bridge of Bordeaux, for the Company of the South railroads when he was the administrator.
Garnier required some modifications, and the agreement was concluded in 1884. The construction was undertaken with celerity and the dome was installed at the Mont Gros by the end of 1885. With a diameter of 22,40m, " the largest of the cupolas which were ever built" declared enthusiastic Camille Flammarion.
"This floating wonder,
he wrote, exceeds of 2 meters the one of the Pantheon", in Paris.
The 76cm-refractor, one of largest of the world,
and the large meridian circle, were to be delivered in 1887. On
this date, the program of the original constructions and projected installations
were carried out.
In 1881, Bischoffsheim had also created an important library, including a collection of six thousand volumes, works and periodicals all taken together, some of them going back to the 17th century, which library is still increasing.
On October 27, 1887, the Observatory was inaugurated with great ceremony, an International Geodetic Congress being hold. Delegates of many countries, members of the Academy of Sciences and the Bureau des Longitudes who participated in it, were welcomed by the mayor of Nice. The emperor of Brazil, Pedro II, attended the last meeting. Festivities complemented the event, which had a very great repercussion in the local press.
The sponsor was praised as he deserved
for this imposing and splendid realization, made without State assistance,
and put at the astronomers' disposal , whereas the State was
unable to provide that to them.