A portable ‘bi-meter’ for measuring both Carbon Dioxide concentrations and temperature, manufactured by Cambridge Instruments in the early 20th century.
The company began manufacturing equipment for the laboratories of Cambridge University in the 1870s. In 1881 it was bought by Horace Darwin, son of the naturalist Charles Darwin (and great-grandson of Erasmus Darwin of Derby). Darwin began developing instruments for use in industry as well as the laboratory, forming a public company in 1895. They demonstrated the first high-temperature CO2 meter at the Physical Society in 1910.
In 1920 after taking over the R W Paul company the name changed to the Cambridge and Paul Instruments Co. The name was shortened again in 1924. The version of the name on the plate of this instrument suggests a date in the late 1920s or 30s.
A portable instrument such as this would have applications in scientific research and in industries as diverse as brewing and mining.
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