Gravity Trains:

Imagine a straight line tunnel right through the Earth connecting two cities, and a train falling through it. This is a Gravity train, and it has been a frequent example in physics books for more than a century. But could such a system actually be built? What new technological breakthroughs would be required? How has tunnel technology evolved during the industrial age so far? Francis Graham (Kent State University) examines this and the prospects of the future high technology required for it in this book, which takes an optimistic look at the future development of human society.