A vane thermometer is not a standard type of thermometer. It's likely you're thinking of a vane anemometer, which is a device used for measuring wind speed.

Here's how a vane anemometer works:

* Components: It has a set of small cups or vanes mounted on a vertical shaft. The cups are shaped in a way that allows them to catch the wind.

* Wind Action: When the wind blows, the cups rotate. The speed of rotation is directly proportional to the wind speed.

* Measurement: The rotation is measured using a counter or an electronic sensor, which translates the rotation into a numerical value representing wind speed.

Key Differences from a Thermometer:

* Function: A vane anemometer measures wind speed, while a thermometer measures temperature.

* Mechanism: A vane anemometer uses the rotation of cups, while a thermometer uses the expansion or contraction of a liquid or metal.

If you're interested in learning more about wind speed measurement, feel free to ask!