Temperature and Pressure Observations by Tommaso Temanza from 1751 to 1769 in Venice, Italy

The study aims to recover, interpret, and analyze the daily meteorological observations made in Venice by Tommaso Temanza from 1751 to 1769. These records are relevant because they provide direct information about the climate of the Little Ice Age. Temanza used a barometer, an air thermometer of Amontons’ type, and an additional mercury thermometer, i.e., Réaumur’s thermometer. These early instruments are presented and discussed in this study. The barometer readings needed standard corrections, which were unknown at that time. The scale of the air thermometer was arbitrary, and temperatures were measured in inches of mercury. For the Amontons thermometer, Temanza missed the calibration points and used a particular scale with the zero-point in the middle of the range. He gave two contradictory explanations for this choice, both of which are discussed in this paper. In the 18th century, the use of a singular value to represent the average temperature, called “Temperate”, was promoted by Michieli du Crest in Geneva and Toaldo in Padua. This work reconstructs the unknown scale, using contemporary observations by Giovanni Poleni and Giuseppe Toaldo in Padua (30 km west of Venice) and snowfall reported in the weather notes to determine the temperature point at 0 °C. A discussion is made about the calibration, validation, and conversion of readings from the original to modern units of pressure and temperature, i.e., hPa and °C, respectively. The recovered record of Venice is presented in comparison with Padua, Bologna, and Milan. The paper provides and analyzes the new dataset, and improves knowledge about the climate, history of science, instruments, and observations made in the mid-18th century.