Introduction:
The instrument used for measuring evaporation is called an atmometer. Evaporation is the process by which a liquid changes into a gas, and it is an important factor to consider in various fields such as agriculture, hydrology, and weather forecasting. To accurately measure evaporation, a specific instrument is required.

Explanation:
The atmometer is a device that measures the rate of evaporation by utilizing the principle of water movement through a porous material. It consists of a cylindrical container with a porous surface, usually made of ceramic, and a graduated tube attached to it.

Working Principle:
1. Evaporation: The water in the container evaporates through the porous surface, creating a water vapor gradient.
2. Water Movement: As the water evaporates, it creates a suction force that draws water from the container and up into the graduated tube.
3. Measurement: The graduated tube is marked with measurements, allowing the user to determine the amount of water that has been drawn up. This measurement represents the rate of evaporation.

Advantages of atmometer:
- The atmometer provides a simple and cost-effective method for measuring evaporation.
- It does not require complex calibration or maintenance.
- The measurements obtained from the atmometer can be used to estimate evaporation rates in various applications, such as irrigation scheduling, water resource management, and climate studies.

Other Instruments:
While the atmometer is specifically designed for measuring evaporation, there are other instruments used in related fields:
- Hygrometer: A hygrometer measures the relative humidity in the air, which indirectly provides information about the potential for evaporation.
- Lysimeter: A lysimeter is used to measure the actual evapotranspiration from a specific area of land. It consists of a container buried in the ground, filled with soil, and planted with vegetation. The lysimeter measures the amount of water that leaves the system through evaporation and plant transpiration.
- Luxmeter: A luxmeter is used to measure the intensity of light, which can affect the rate of evaporation indirectly in certain situations.

Conclusion:
The atmometer is the instrument specifically designed for measuring evaporation. It operates on the principle of water movement through a porous surface and provides a simple and cost-effective method for estimating evaporation rates. Other instruments, such as hygrometers, lysimeters, and luxmeters, are used in related fields to indirectly measure factors that affect evaporation.