George Waltemath made an extraordinary claim: that the Earth had a second moon. It was supposed that it was much smaller and dimmer than the known moon. He predicted that on February 3rd of 1898 it would be visible in silhouette as it moved across the disk of the Sun, an event known as an astronomical transit.
Winslow Upton was skeptical of the existence of this long unnoticed moon, but nonetheless attempted to observe it.
Discover the story of Waltemath's "Astronomical Blunder" at the Ladd Observatory blog: