What happened to Vulcan between the late 1870s and the early 1900s

Determine what occurred to the purported intramercurial planet Vulcan between the late 1870s, when multiple observations reported transits and eclipse sightings, and the early 1900s, when photographic searches during total solar eclipses failed to detect it, thereby explaining the apparent disappearance from observational records.

Background

The paper reviews 19th-century reports of an intramercurial planet, Vulcan, including transit observations and eclipse-time sightings that supported its existence. Despite substantial attention and periodic observational claims in the 1860s and 1870s, early 20th-century photographic searches during total solar eclipses, notably by the Lick Observatory in 1908, did not detect such a body.

The authors propose two plausible mechanisms that could reconcile the earlier reports with the later non-detections: significant orbital alteration via gravitational scattering (potentially linked to the Great Comet of 1882) and long-term inclination–eccentricity exchange through the von Zeipel–Lidov–Kozai mechanism driven by Mercury. The explicit unresolved question centers on identifying what, if anything, happened to Vulcan in that interval to remove it from the previously searched regions near the solar equator.