I have Bill Bryson's "A Short History of Nearly Everything." It is divided in small chapters, typically 10-20 pages each, contain a brief history of a concept, thing, or event. Perfect for a 15 minute break.

Check out the classic BBC TV series Connections (1978) hosted by James Burke - this page includes a summary of the episodes. Each episode is an hour, however. Burke wrote a [companion book](http://en.wikipedia.org/wiki/James_Burke_(science_historian)#Books) for the first series.