The Second Great Advent Movement, while not a book about or by thye Watchtower Movement, it is a history of William Miller and the legacy he legt behind, the Second Adventist. Written in 1905 this was published by the 7th Day Adventist. a Much beter read than the "Proclaimers Book".
http://205.134.162.24/downloads/1905_The_Great_Second_Advent_Movement.pdf