What is used to measure wet bulb temperature?

The correct answer involves the use of a wet wick around a thermometer. This method is essential for measuring the wet bulb temperature, as the wet bulb temperature is the lowest temperature that can be reached by evaporating water into the air.

When a thermometer has a wick that is kept moist, the evaporation of water from the wick cools the thermometer's bulb. The drier the air, the more evaporation occurs, leading to a lower reading on the thermometer. This measurement reflects humidity levels in the air, making it a significant factor in calculating other indices, such as the heat index or humidity ratio.

A psychrometer typically consists of a pair of thermometers—one with a wet wick (wet bulb) and one without (dry bulb). In this context, the correct choice is more specific and directly involves the use of the wet wick to accurately gauge the wet bulb temperature through the mechanism of evaporative cooling.