The thermometer is an instrument use to measure temperatureA thermometer is an instrument used to measure temperature, which tells us how hot or cold something is. It plays an important role in observing the weather because temperature is one of the main elements in understanding the weather. For example, whenever the dry season arrives in the Philippines, we have something called the "heat index" to get the heat index at a particular station in an area, they use a thermometer, so that they can make an accurate forecast of the temperature in that area.