How does elevation affect the reading of a barometer?

The correct choice highlights the fundamental principle of how a barometer operates in relation to elevation. As elevation increases, the atmospheric pressure surrounding the barometer decreases due to the thinning of the air at higher altitudes. This means there is less air above the barometer exerting force, leading to a reduction in the weight of the atmosphere.

The barometer measures air pressure, so when you go higher in elevation, the air pressure decreases, and consequently, the barometer's reading will reflect this decrease. This is because the barometer, typically filled with mercury, will show a lower level of mercury in response to the reduced external atmospheric pressure.

Understanding this relationship is crucial for accurately interpreting barometric readings in high-altitude environments and is fundamental knowledge for anyone involved in meteorological studies, aviation, or mining operations, where altitudinal changes may impact safety and operations.