The Perrault building, while certainly a magnificent structure, was never well suited for astronomical observations. Thus, during the 18th century various more or less appropriate annexes were added, and a small observatory was built on the renovated terrace, with two instruments and a rain gauge; the latter might seem to be a surprising element, but in fact the Observatory had become an important meteorological centre.

caption : The Observatory in 1829 - credits : Observatoire de Paris