Unknown Quantity was part of my last year’s advent calender. A surprise since it was not on my wish list. Yet, it could have been on the list as I am – at least once in while – interested in math, or the history of math.
Unknown Quantity traces the history of algebra from its roots to modern times. While it seems quite comprehensive concerning the earlier phases of discoveries it becomes rather patchy in describing the development during the, say, last hundred years. Of course, a lot was happening during these years and most can only be understood with a proper degree in mathematics. A fact that led the author John Derbyshire (apparently quite a character) to add some more technical notes (on the easier topics) to the historic accounts and biographical notes.
The book is rather interesting and informative; though certainly it is not the authoritative source on the history of math, or even just algebra.