Ein ganzes Buch über die Relativitätstheorie im Volltext. (via Der Schockwellenreiter).

But who is the author? The domain mathpages.com at least belongs to Kevin Brown. From th epreface:

This book examines the evolution of the principle of relativity in its classical, special, and general incarnations, both from a technical and a historical perspective, with the aim of showing how it has repeatedly inspired advances in our understanding of the physical world.