Update: Adamstown UFOs (1869)

I've since found that, though it's not mentioned in the original article, on the day of the sighting there was also a solar eclipse. The solar eclipse did produce luminous phenomena (seen by astronomers in Kentucky, Iowa and Ohio) which were seen crossing the eclipsed disk. Being those lights were in the air, I'm not sure how they're relevant to ground-based phenomena, but they could be.