This book was printed in 1827 by what turned out to be a former husband of one of Joseph Smith's polygamous wives. This book illustrates the Masonic initiation rite prior to the LDS Endowment in the 1840's which match almost exactly in the penalties, signs, grips, five points of fellowship, etc. that existed in the early endowment (even though some of those items don't exist anymore in the endowment and didn't exist in freemasonry until just prior to the 19th century).
Heber C. Kimball's (who was in Brigham Young's presidency and helped to write the endowment) daughter said, "I remember once when but a young girl, of getting a glimpse of the outside of the Morgan's book, exposing Masonry, but which my father always kept locked up." (Heber C. Kimball: Mormon Patriarch and Pioneer, page 12)
For more on the history of freemasonry see: The Temple and the Lodge and Holy Blood, Holy Grail.
For more on Morgan and early Mormon polygamy see this page.