Pair of resonating bowls

I chanced upon this pair of concrete resonating sound reflecting bowls in a sensory garden in the Kew Riverside development off the towpath between Chiswick Bridge and Kew Railway Bridge. there is probably a proper name for these bowls, but I don't know what it is.

If I hadn't been on my own, I'd have tested them out! As it was, I contented myself with blipping them.