Pyrometer of Musschenbroek, Jan Paauw Jr., Leiden, c. 1759 Inv V09550

Petrus van Musschenbroek, the successor of 's Gravesande, continued the latter's work on the Physics Theatre. He himself designed a number of pieces of experimental apparatus, such as this pyrometer, with which the expansion of metals could be determined. This was done as follows: a liquid was poured into the metal tray with the wooden handle (to prevent one burning one's fingers). This might be water, oil or alcohol. This liquid was brought to the boil by the burners placed beneath it. In the liquid was a metal rod. Due to the heating this rod expanded. As a result it pressed against another rod outside the tray attached to a meter. From the meter it was possible to read off how far the metal rod in the liquid had expanded.By doing this with different kinds of metal, Van Musschenbroek was able to investigate the difference in expansion.