The wonderful Flatland: A Romance of Many Dimensions, by a Square is now available for free download from Google Books.

It is a part of Google’s latest effort to offer free downloads of their public domain books. Search for “free books” to find more.

For the uninitiated, Flatland is a fun introduction to one-dimensional and two-dimensional thinking. Plus the concepts developed by it can then help one visualize some of the basics of General Relativity.