The earliest temperature record in Paris, 1658-1660, by Ismaël Boulliau, and a comparison with the contemporary series of the Medici Network (1654-1670) in Florence

The earliest temperature series in Paris, from May 1658 to September 1660, taken by Boulliau has now been made available at daily resolution after a careful work of homogenization, correction and calculation of the average values. New results have been achieved concerning the Little Florentine Thermometer, building location, thermometer exposure, observations methodologies followed by Boulliau and the climate in the mid 17th century. Two methods have been used and compared to calculate the daily average from readings taken at random sampling times. The first one is based on the reading needing the smallest correction to be transformed into a daily average; the second considers all the readings of the day and makes a bulk average of the individual results. The series has been compared with the temperature record by the Grand Duke Ferdinand II in Florence, that was the primary station of the Medici Network (1654-70). In addition, the comparison of the earliest temperature series in Paris and Florence with their respective 1961-90 reference period give a clear image on the climate in Europe in the middle of the 17th century. Key features were a strong variability for warm-air and cold-air outbreaks, severe winters and cold summers in Paris, not affecting Florence.