At the moment I am reading The Calendar by David Ewing Duncan. This is a nice little book which covers the history of the calendar. Its brief takes us from carving notches on bones to count the days between full moons to trying to establish a true length for the year (and prevent the calendar drifting compared to the seasons).
The book encompasses science (astronomical measures), maths (being able to specify fractions of a day), religion (the date of easter) and history. It seamlessly takes us on a chronological journey through the ages.
I like cross-curricular books, my favourite books tend to be those which span subjects, as there is something familiar to take us on into the unknown. Also one can spot how one discipline feeds off another, other books of this ilk include Dava Sobel's "Longitude" and William Poundstone's "The Prisoner's Dilemma".