Observatory of the Roman College seen from the Calandrelli Tower. The reproduction shows in order: 1) bundle of electric cables for the transmission of the signals of the meteorological sensors located on the Calandrelli Tower to the Secchi’s automatic Meteorograph; 2) pole with wicker ball, used, starting from 1847, to signal midday to the artillerymen of Castel S. Angelo; 3) dome with the Merz telescope; 4) elliptical observatory for the meridian circle of Ertel; 5) dome with the Cauchoix telescope; 6) electric turret observatory with the small ball conductor; 7) Median Terrace of the Calandrelli Tower. From Secchi’s communication L’astronomia in Roma nel Pontificato di Pio IX (Secchi, 1877).