I did post a link to a digitized manuscript of Barrett's above.. having brought up the info from the RAMS version, its occurred to me its probably at least part of the basis of the 1801 version.

Its not hard to miss Barrett - he didn't do much. I think "The Magus" and "Lives of Alchemystical Philosphers" are his only publications. The source material for the Magus, like the Key of Solomon and Agrippa's books of occult philosophy was never that rare.. and probably superior to his summary. I don't think he was ever that popular or got much traction.

And since then, for the material he covered, he kind of got buried by the Golden Dawn and Theosophists, and the whole Spiritualism thing.

There's various claims made about Barrett online, like his work translation "kabbalistic texts" and whatnot, but I see no proof of that anywhere.