Mercury thermometer probably built by Felice Fontana, comprising a pear-shaped bulb and a long broken tube, mounted on a wooden board with the scale marked on paper. The board is hinged and folds flat when the clasp is released.

On the back are the following notations in Fontana's handwriting: "a, a, indicates the degree of frost found in June 1784, whence it appears that the mercury falls lower in summer than in winter. This observation is confirmed by the two Sample Therm[ometers] divided into 500 on the glass plate" And also: "The zero indicates frozen water compared with the perfect Therm[ometer]. The no. 4. over the freezing mark indicates 4 degrees above frozen water measured with the perfect Therm[ometer] in 1783 in the July summer." Fontana's studies on cold were certainly inspired by the research conducted shortly beforehand by the French chemist Antoine-Laurent Lavoisier.