What instrument is used to measure dry bulb temperature?

The standard mercury thermometer is the correct instrument to measure dry bulb temperature because it accurately indicates the air temperature by measuring the thermal expansion of mercury in a calibrated glass tube. This type of thermometer does not take into account humidity or other factors that would affect temperature readings in specific environments; it simply provides a straightforward measurement of the ambient air temperature.

In contrast, a digital thermometer also measures temperature effectively but is not typically classified as specifically measuring dry bulb temperature in traditional contexts where a mercury thermometer is standard. A wet bulb thermometer is designed to measure the temperature of evaporative cooling and reflects humidity levels, while a psychrometer uses both a dry and wet bulb thermometer to calculate relative humidity, thus not focusing directly on the dry bulb measurement alone.