This wall thermometer was made in Madrid in the second half of the nineteenth century by José Grasselli, who held the title of “optician to His Majesty” in recognition of the scientific instruments he made for the Royal Household. It consists of a wooden box with a brass plate screwed onto it, attached to which is the capillary glass tube containing the alcohol. The lower part of the tube ends in a spiral with a decorative and artistic intent besides its scientific function of precise measurement.

It has the two most common temperature scales of the time: degrees centigrade (from -27oC to 69oC) and degrees Réaumur (from -21oRe to 55oRe). Although the Réaumur scale has fallen into disuse, it was widely used at the time in France, Germany and Russia.

Thermometers of this type have engraved inscriptions with various temperature references, some of them common and others more unusual. Among the most habitual were the appropriate temperature for breeding silkworm (23.7oC), extreme temperatures like the maximum recorded in Paris (38.7oC in 1802) and the minimum (-19oC in 1838), and the freezing point of water (0oC). Also included were the temperatures of certain localities like Syria and Senegal.

José Grasselli was one of the founders of the establishment Grasselli y Zambra (c. 1840), reputed as one of the first shops in Spain to specialise in the production and distribution of precision instruments. Its offer covered a wide range of disciplines, from optics, physics and mathematics to geodesy, mineralogy, astronomy and surveyance. After 1864, José Grasselli continued to carry on the business independently at number 5, Calle Montera.

Both Grasselli y Zambra and the establishment run by José Grasselli were purveyors of scientific material for schools and scientific societies. They also supplied scientific instruments to prominent institutions like Banco de España and the Royal Palace of Aranjuez. Preserved at the latter is a thermometer signed by Grasselli and Zambra that predates their appointment as “opticians to His Majesty” in 1849.

Rosa María Martín Latorre