The 1730 eruption of Mount Vesuvius and Hauksbee’s thermometer

As a correspondent for Jurin's meteorological network, Niccolò Cirillo conducted intense observation and data collection in southern Italy from 1723 onwards, including observations of earthquakes and eruptions.
The eruption of Mount Vesuvius in March 1730 attracted Cirillo's attention: he wrote a detailed report, which he then sent to the Royal Society. The report began with a comment on some critical issues related to the use of Hauksbee's thermometer, which Jurin had provided to all participants in his meteorological network with the aim of standardizing measurements and methods. Cirillo offered a possible explanation for the discrepancy observed between the freezing points of water in Naples and London, identifying its cause in the saline nature of the air in Naples (very different from that in London).
Hauksbee's first thermometer consisted of a long, thin tube, terminating at the lower end in a hollow sphere filled with wine spirits. The rarefaction and subsequent rise of the spirits could be estimated from the number of divisions on the tube, thus allowing the measure of the temperature of air or any other liquid. The tube featured a scale with twenty-three divisions, which alluded to the adoption of the original unit introduced by Robert Hooke: this thermometric unit, 1°H, was later found to be approximately equal to 2.4°C. Later, in 1720, Hauksbee modified this standard, changing Hooke's twentieth scale, which had its origin at the freezing point of water, to an inverted centesimal scale, whose unit was equal to one-fifth of Hooke's unit (and therefore approximately equal to 0.5°C).
After focusing on Hauksbee's thermometer, Cirillo went on to describe in detail the eruption of Vesuvius, which developed with the characteristics of an effusive Strombolian event and ended with the collapse of its summit. In his report, he also described the atmospheric conditions, which he believed were closely related to volcanic activity.

___Salvatore Esposito & Adele Naddeo