50.5 MB (6.5 MB compressed)
5062 x 3484 pixels
42.9 x 29.5 cm ⏐ 16.9 x 11.6 in (300dpi)
CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Home thermostat. The dial at lower left is used to determine the temperature at which the central heating system will turn itself off. To do this, a vial of mercury (centre right) is attached to a bimetallic strip (coiled, upper left). The strip contains two metals that expand at different rates on heating. This means that the strip as a whole bends during heating, with the metal that bends more on the outside of the curve. In this thermostat, the dial rotates the entire mechanism. When the temperature in the room rises to the set point, the mercury flows away from the contacts, breaking the electrical circuit and thus switching off the heating.
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