Weksler Model 322 US Weather Bureau Maximum and Minimum Thermometers
This is a Model 322 pair of maximum and minimum temperature thermometers made by the US firm Weksler Thermometer Co. It includes a Townsend support, which holds the thermometers in the correct orientation for operation, reading and resetting. I believe it dates from the 1940s or 1950s, it's shown in the 1958 Weksler catalog available on this website. It was formerly used at a US Weather Bureau climatological station in Minnesota. The thermometers are 12 inches long.
The minimum temperature thermometer is spirit-filled and contains a float which moves down with the fluid to the minimum temperature. When the temperature rises again the float is left behind, recording the minimum temperature reached since the last time it was reset. It is reset by rotating the thermometer to upside-down, which can be done on the support. The float then sinks to the top of the fluid, which is indicating the current temperature. The range is -65 F to 100 F.
The maximum thermometer is mercury-filled. It contains a constriction in the lower end of the glass tube. As the temperature rises the mercury is forced through the constriction. When the temperature then drops, the mercury cannot flow back though the constriction and is left indicating the maximum temperature reached. It is reset by spinning the thermometer on the support. The centrifugal forces pushes the mercury through the constriction, so that it again indicates the current temperature. The range is -38 F to 110 F.
