Full Idea
A wave is maintained by a process transferring motion from particle to particle of the medium, but it is not identical with this process.
Gist of Idea
A wave is maintained by a process, but it isn't a process
Source
Peter Simons (Parts [1987], 8.5)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.308
A Reaction
I'm inclined to think of the mind as a process. There are some 'things' which only seem to exist if they have a duration. Bricks can be instantaneous, but minds and waves can't. A wave isn't a continuant. A hill isn't a wave.