::::No, the Schofield text rarely makes claims of the "first" sort. That is one of its major problems, actually. It doesn't effectively place Priestley in his historical milieu. I had to rely on other sources, such as Tapper to do that. Most of the generalized statements about Priestley's importance do not come from Schofield. I would not rely on the JP: A Comet in the System book. It is not the most reliable text we have (see publication information) and citing a dissertation is, sad to say, not the first line of defense. I already listed that Schofield quote above, which shows Priestley's indebtedness to other eighteenth-century thinkers. That list is more reliable, in my opinion. 

I agree that Schofield is partial to Priestley. It was kind of frustrating, actually, because it was the most complete account of Priestley there was.  | talk