So, I've just come across another Ring of Invisibility I hadn't known about before.
It's in the work of an author whom Tolkien certainly read, though I don't have specific evidence of his reading this particular work.
Best of all, this marks the first time I've found a Ring of Invisibility in a fantasy novel before JRRT.
More details to follow.
concert review: Murray Perahia
4 hours ago