Published In 1801 by Francis Barrett, this work was meant as a textbook for classes in magick that Barrett was offering at No. 99 Norton St., Marylebone- at any time between the hours of eleven and two o’clock. It would appear that he was attempting to found a magickal order, which may or may not have succeeded.
As for the content of the book, I’m afraid we have to class this text with the others that have taken so much from Agrippa’s Three Books… and those which came directly after. It consists mainly of large portions of Agrippa’s work (specifically portions of the first and second books), along with large chunks of the Magickal Elements and Fourth Book of Occult Philosophy thrown in. Many tend to consider Barrett a plagiarist, as he leaves his sources (which he does indeed quote word for word in most cases) unaccredited. Although, I tend to feel that Barrett (operating as late as the 1800s) was simply compiling a workable textbook for his class from the sources he had personally tracked down and studied. In fact, The Magus seems to represent a last revival of grimoiric material before the Victorian work of Eliphas Levi, and the Golden Dawn after him.