Put the softened, not melted, butter in the little one and cold water in the big one. Then set the little one into the big one.
Keeps butter soft for a few weeks. (Oh? I'd use it by then for sure.)
This means that it is spreadable and doesn't get rancid as quickly.
(Oh? I never had any rancid butter, anyway.)
Perhaps this is for use by those who make their own butter and have no refrigeration and like spreadable butter.
Here's a link to explain butter bells:
http://www.webexhibits.org/butter/crocks.html
This one I titled Misfit as it just fits if you turn it to a certain spot. It's so cute. But I really think butter bells are silly.
I may try it anyway.
This one doesn't hold much butter.