I'm not sure where or how you would access a copy of this, but here is an article specifically on the paintings (I'm not sure if there ever was a Part 2 though!):-
Stephen R. Gilbert. “An analysis of the Xavier della Gatta Paintings of the Battles of Paoli and Germantown, 1777: Part I.” Military Collector and Historian, no. 3 (Fall 1994). p. 98-108.
It used to be possible to contact the author on this website, which is a mine of info and the members are very helpful if you have specific queries on these paintings:-
http://groups.yahoo.com/group/Revlist/