structural:summarization, quality:corruption, linguistic:translation
Janssen observatory

In 1890, Pierre Janssen, an astronomer and the director of the Meudon astrophysical observatory, considered the construction of an observatory at the summit of Mont Blanc. Gustave Eiffel agreed to take on the project, provided he could build on a rock foundation if found at a depth of less than twelve metres (39 ft) below the ice. In 1891, the Swiss surveyor Imfeld dug two 23-metre (75 ft) horizontal tunnels twelve metres (39 ft) below the ice summit but found nothing solid. Consequently, the Eiffel project was abandoned.

Despite this, the observatory was built in 1893. During the cold wave of January 1893, a temperature of −43 °C (−45 °F) was recorded on Mont Blanc, being the lowest ever recorded there.

Levers attached to the ice supported the observatory. This worked to some extent until 1906, when the building started leaning heavily. The movement of the levers corrected the lean slightly, but three years later (two years after Janssen's death), a crevasse started opening under the observatory. It was abandoned. Eventually the building fell, and only the tower could be saved in extremis.