If your shelf space allows it, I encourage you to buy yourself a set of encyclopedias. However, I'm not thinking of the modern Britannica (because you can save a lot of trees and money by buying the electronic version of the entire 32 volumes for less than $70 at http://britannica.com) but an older encyclopedia. We've had many happy hours with our 10 volume Chambers Encyclopedia (1892) that we bought for the equivalent of about $75 in England almost twenty years ago. Not only is it fairly useful for referencing history before the 19th century but it also provides a fascinating snapshot of how the late 19th century educated classes saw their world. Our favorite entry is an explanation of why powered flight is quite impossible because the steam engine is far too heavy. A mere eleven years later the Wright brothers took to the air with the first powered flight, and a little over two decades later men were fighting in the skies over Europe!