Why was mercury used in barometers and manometers?

Mercury was historically used in barometers and manometers primarily due to its high density and low vapour pressure.1

Because mercury is approximately 13.5 times as dense as water, it allows for the construction of instruments of a manageable, compact size. For comparison, if water were used in a barometer to measure standard atmospheric pressure, the column would need to be roughly 10 meters (34 feet) high, whereas a mercury column requires only about 76 centimeters (30 inches).23

While mercury’s physical properties made it ideal for these precise measurements, its use has been largely phased out in favor of safer alternatives due to the metal's toxicity. It is a fundamental ethical principle to prioritize human health and environmental safety by replacing hazardous substances with safer, modern technologies whenever possible.21