What feature of mercury-in-glass thermometers allows for the measurement of temperature?

The measurement of temperature using mercury-in-glass thermometers is primarily based on the calibrated length of the mercury column. As temperature increases, mercury expands and rises in the glass tube, allowing for the measurement of temperature based on how high the mercury rises.

The calibration of the thermal scale is marked on the glass tube, correlating specific lengths of the mercury column with specific temperature readings. This visual representation enables users to easily read the temperature at which the mercury column settles. The precise, predictable expansion of mercury with temperature makes this method effective and reliable for various applications.

Other features, such as the type of glass or the viscosity of mercury, may contribute to the functionality of the thermometer but do not directly enable temperature measurement. Additionally, while mercury does conduct electricity, its electrical conductance is not relevant to the operation of a traditional thermometer. Instead, it is the relationship between the calibrated length of the mercury column and temperature that is central to the thermometer's design and purpose.