Psychrometer  mod. Cantoni, belonged to De Marchi. First half of the last century. This instrument measures the atmospheric humidity. It is made by two thermometers, one with the bulb in air and the other with the bulb wrapped in a moistened tissue. This second thermometer measures a temperature lower than the previous one because the water evaporation requires heat, lowering the temperature measured of an amounts inversely proportional to air humidity. From the readings of the two thermometers it is possible to know the relative and the absolute air humidity by turning a mobile slide included in the frame hosting the two thermometers. This psychrometer dates back to the first half of the last century. It was built by Angelo Cattano, mechanic of Royal College Beccaria of Milano, according to the plan of the physicist Giovanni Cantoni, Director of the Central Meteorological Service from 1874.