Rita

I am pretty sure that it is Sophia's husband. One of the books that I have is The Thrales of Streatham Park by Mary Hyde published by Harvard University Press in 1977.

In this book is a painting of Henry Merrik (no c) Hoare by the painter Woodforde (shown above). In the bottom left corner (if you look carefully) it says "Henry Merrick [with a c] Hoare Born 1779).

The real way to tell is to see if your book gives any information about Henry that can be verified against what we know about Sophia's husband. Things like relatives names, places of abode, occupations etc. If the book has any of this info I might be able to confirm this with some more certainty.

I hope that this helps. By the way you didn't mention which book it was that had the plate you are researching.