My sleuthful colleague wrote to "LiveAuctioneers.com" to ask for information about the provenance of this painting of Admiral Cyrus Blake of (it is thought) Boston.
I can appreciate your frustration! May I suggest it is by another notable artist - a protege of Stuart's - James Frothingham?
If in fact Cyrus Blake was from the Boston area -
and given the period attire - you still have a valuable portrait on your hands!
Good luck in your investigation!
All good wishes.