The dilatometer is an instrument used to measure changes in length or extent suffering different metal rods. This type of device was invented and described in 1731 by Petrus Van Musschenbroek (1692-1761), Dutch physicist, and named pyrometer (though now known as dilatometer). The dilatometers of XVIIIth century were used by watchmakers because of the need to analyze the thermal properties of the metal rods and were used for physics experiments on cabinets. The model that you see in the picture is similar to that described by Nollet (1700-1770) in his "Leçon de Physique experimentale" (1764). Our piece is from the second half of the eighteenth century, made by the Spanish scientific instrument maker Juan Gonzalez in 1772.