Question

In his 1812 treatise on barometric hypsometry, physicist Pierre Louis Dulong demonstrated that early nineteenth-century measurements of atmospheric pressure at elevated altitudes were systematically distorted not by thermal expansion of the instrument's brass scale, as contemporary meteorologists had widely asserted, but by the meniscus depression resulting from capillary action within narrow-bore glass tubes. Dulong observed that while thermal variations could be readily offset using standard linear correction tables, capillary depression varied non-linearly with internal tube diameter and was frequently omitted from calculations. Consequently, observations conducted with tubes measuring under four millimeters in internal diameter underestimated baseline sea-level pressure by up to two millimeters of mercury. To rectify this discrepancy without replacing existing inventory, Dulong devised an empirical adjustment chart that calibrated raw pressure readings against measured tube bores, though he explicitly cautioned that this correction applied exclusively to unrefined mercury columns free from surface oxidation.

According to the passage, Dulong identified which of the following as the primary cause of systematic distortion in early nineteenth-century high-altitude barometric measurements?