Metal thermometer operated by the thermal expansion and contraction of a metal rod (probably made of lead). The rod is housed in a glass tube and mounted on a slate base with an inverted T shape. The lower part of the rod acts on a pair of identical mechanisms consisting of two pointers, moved by toothed wheels meshing with racks. The pointers are placed in such a way that one of them indicates, on a thermometric scale, the maximum temperature reached (corresponding to the minimum length of the rod), while the other records the minimum temperature. The pointers, scales, and transmission mechanisms are enclosed in a brass box with a glass front.