The method of levelling in which the heights of mountains are found by observing the temperature at which water boils, is known as

Explanation:

Hypsometry

Definition: Hypsometry is the method of determining the heights of mountains, hills, or other elevated terrains by observing the temperature at which water boils. This technique is based on the principle that the boiling point of water decreases as altitude increases due to the reduction in atmospheric pressure.

Working Principle:

The principle of hypsometry relies on the relationship between atmospheric pressure and the boiling point of water. As altitude increases, atmospheric pressure decreases, which, in turn, lowers the boiling point of water. By measuring the temperature at which water boils at a particular location and comparing it with the standard boiling point at sea level (100°C), the altitude of the location can be determined. This method is particularly useful in remote or rugged terrains where other methods of levelling might not be feasible.

The mathematical relationship between altitude and atmospheric pressure can be used to calculate the elevation. This relationship is derived from the barometric formula, which considers factors such as the decrease in pressure with height and the temperature of the atmosphere.

Advantages:

• Does not require sophisticated equipment; a thermometer and a standard reference chart are sufficient.
• Useful in remote and inaccessible areas where other levelling methods cannot be employed.
• Relatively simple and quick to perform compared to other levelling techniques.

Disadvantages:

• Less accurate compared to other levelling methods, such as spirit levelling or GPS-based techniques.
• Accuracy is affected by variations in atmospheric conditions, such as temperature and humidity.
• Not suitable for applications requiring high precision.

Applications:

• Determining the height of mountains or elevated terrains in geographical surveys.
• Used in exploratory expeditions and mountaineering to estimate elevations.