Rumford thermoscope, C 1890
A French differential air thermometer or Rumford thermoscope, circa 1890,
stamped Breton fréres a Paris. With one bulb in line with a radiant heat source, and the other well clear, the expansion of air is indicated by a thread of alcohol in the horizontal tube.
The two glass spheres connected by capillary tube with scales, on turned mahogany stand. 43 cm high.